T losing power when hot

[RadRacer203]

Wondering if anyone might have suggestions on what I should look for, I took my '26 coupe out for a longer drive today to test out my new exhaust, and it seems like it's losing power when the engine gets good and hot. The first mile or so I was flying along, probably as fast as I've ever taken the car, and it was running amazing. After a little bit though it started feeling down on power and a squeak started under decent load/rpm.

This squeak is definitely not the pistons expanding and seizing, it didn't do that when the engine was boiling over when my timing was way out. Haven't figured out what it is and it only does it when the engine is good and hot, and driving.

I wouldn't say the car was really struggling, but it didn't want to go faster than what felt like 30 when it was going what felt like 40+ before. The engine is stock aside from a Waukesha Ricardo head and aftermarket timer, and is standard bore and has likely never been apart as far as I can tell. The carburetor seems fine, the coils, plugs, timer, head gasket and manifold gaskets are new and sealing well, and it has an aftermarket water pump (which I think may be what's squeaking).

So far my ideas are maybe the valve lash is too tight, or maybe carburetor? I gave the valves a cursory glance when I had the valve cover off and there wasn't anything obviously wrong. Didn't measure but all of them had at least some lash, and it looked good enough. The carburetor I haven't pulled completely apart yet, but it seems to be working fine, and changing the mixture doesn't affect this issue

[Norman Kling]

Several things we need to know to be able to diagnose the problem.
1. You don't state what year the car is. This would make a difference due to the location of the gas tank.
2. You don't say whether or not the coolant level changed. If it dropped below the center of the top tank on the radiator, it could cause it to overheat.
3. You don't state whether or not you have a thermostat.
With the information you did give us, it shouldn't overheat in winter in Vermont. If you were going uphill, it might slow down a bit.
If your tank is in the back or under the seat, the location of the fuel line could cause a problem. If there is a high point between the tank and the carburetor, you could have vapor lock, especially if the line is close to the exhaust pipe. If the fuel level is low in the under seat or back seat of the car, and you go uphill, you could be starving for gas or same if you are using a fuel filter other than the standard sediment bulb. If the screen in the sediment bulb is clogged with debris, you could starve for fuel.
If it gets hot this time of year, you will have bigger problems when summer comes.
Sometimes, a leaky head gasket can sound like a squeak. It is caused by compression under combustion leaking through the head gasket. If the head or block is not flat or if the bolts are not torqued property, it could cause it to leak. The question would be after the car cools down, is the coolant low? That would indicate it either steamed or leaked out. Less likely to have these problems with the 26-27 with the cowl tank. But could still happen with a clogged sediment screen or with a filter. How is the pulley on your water pump? I only had one car with a water pump and the pulley was loose and possibly the pump tight. The set screw holding the pulley cut a groove in the shaft like it had a lathe. I took off the pump and installed the stock inlet and no more problems.
If the engine was running too hot, your piston might even be scoring the cylinder but not expanded enough to seize the engine.
A lot of things to check, I know, but first thing I would do is check anything you did or installed since the last time you drove that it didn't overheat.
Norm

[Allan]

Two things to check. First, check your speed. IMHO, 40mph is punishing in a standard T. It would be happier at 30 mph. Second, lubricate your fan pulley well and see if the squeal goes away.

Allan from down under.

[RadRacer203]

I'll definitely re-torque the head next time I work on it, I haven't checked since I installed the new head. It's a '26 coupe, no thermostat, and the coolant is very slightly low. The water pump was stuck when I got the car, but I freed it up, greased it, checked the pulley, but it might be a bit sticky still. It spins when the engine is running though. Gonna put a bit of that scale remover in before I flush the block when it gets warmer.

[RadRacer203]

Two things to check. First, check your speed. IMHO, 40mph is punishing in a standard T. It would be happier at 30 mph. Second, lubricate your fan pulley well and see if the squeal goes away.

Allan from down under.

Ok, good to know. I did redo the fan bearings but it might need some extra grease after I've driven it a bit. I don't need to drive at 40 constantly, but it just didn't seem to pull nearly as hard up hills the latter half of my drive, that's what I'm trying to solve

[Norman Kling]

If you have a good radiator, the water pump is not necessary. I agree that pushing it to 40 mph is straining a bit. But it should go that fast, maybe not constantly. If you put anything else on the car that was not there before, it might be the problem. I once got a high volume intake manifold which I installed on the car. I had a standard NH carburetor. The car was slow. Then I installed a standard T intake manifold and it goes starts out much better. It ran on level at higher speeds with the high volume intake, but slow pickup to fast speeds. Try blowing out a candle or match with your mouth open wide. It puts out a lot more air, but if you pucker your lips the air will focus on the flame and put it out. So with the right kind or other equipment, the intake manifold would have worked fine, but with everything else standard, it didn't work so well. This included trying to start out fast with wide open carburetor as well as pulling hills with wide open carburetor.
Norm

[Jerry VanOoteghem]

I'll definitely re-torque the head next time I work on it, I haven't checked since I installed the new head.

To my thinking, the re-torque will come too late. Your squeak under load is almost definitely a head gasket leak as a result of not retorquing soon enough. I hate to say, I've heard it too many times myself. You can retorque now and see what happens, but I've never been able to save a head gasket once it has leaked like that. You sould also be concerned now about a possible coolant leak.

If/when you install another head gasket, use copper coat sealant, torque the head, let it sit for a few hours, run the motor until hot, (whithout actually driving the car), let it cool down, then retorque the head. The main thing is, don't go driving the stink out of it until you've properly retorqued the head.

[Allan]

Micheal, if you redid the fan pulley bushings, you might just have made a too good fit. When the pulley and bushes get warm, they will expand and close down the clearance on the shaft. They do squeal when they get dry, right before they seize. The waterpump is an added complication. It needs more belt tension to drive it. It reduces the wrap on the fan pulley, meaning it too needs more tension. I'd be bypassing the water pump with a standard fan belt in place, just to see if the pump was needed.

Allan from down under.

[Art M]

I know a person who removed his waterpump on an overheating engine and the overheating problem totally disappeared.
I basically like the idea of waterpumps and I have one on my car. It came with the car 47 years ago.

Art Mirtes

[Norman Kling]

When you torque the head be sure to start in the center and work out to the front and back alternating from side to side as shown in the diagram in the manual. With the steel head, torque when you first install it then torque again when it has warmed up before you drive the car. With an aluminum head torque when cold then after you warm it up, let it cool down before you re=torque it. Continue to do this until it holds it's torque.
Norm

[RVA23T]

Did you reinstall your Hot Air Pipe for the carburetor? one of previous post showing your new head, the pipe is not present and you might be experiencing icing up in the carburetor.

[Adam]

Drive it until it noticeably bogs again for a while then immediately pull over, leave it in neutral, and turn engine over with the hand crank. If the engine is at all stiffer than it was when the engine was cold, your most likely issue is: Piston clearance to cylinder and/or wrist pin clearance to piston. The stiffness of the engine hot may only be barely noticeable. It sometimes doesn’t take much to consume a noticeable amount of power.

Proper wrist pin clearance is commonly overlooked on Model T’s by even some “experienced” engine builders. The piston pin bores always require at least a little line honing to align them and bring clearance into spec.

The clearance specs listed on the new piston boxes for the last several years are also too tight.

If the engine hot is absolutely as free as it was cold, then the problem likely lies in the drivetrain or rear axle.

[Norman Kling]

Another thing which could cause drag would be bent connecting rod. If it is crooked in the direction that the wrist pin would be lower on one side than the other, the skirt of the piston would drag in the cylinder. Also more noticeable if you have aluminum pistons because they expand at a greater rate than steel, so too tight when cold might move fine but when hot they drag the cylinders. This could also lead to scoring of the cylinder walls and burning oil.
Norm

[Mark Gregush]

Could be as simple as running too lean and not enough advance on the spark or coil issues. Might be time to clean the carb and adjust/rebuild the coils if/as needed. Mine with rebuilt engine was happy between 35 and 37ish.

[speedytinc]

Drive it until it noticeably bogs again for a while then immediately pull over, leave it in neutral, and turn engine over with the hand crank. If the engine is at all stiffer than it was when the engine was cold, your most likely issue is: Piston clearance to cylinder and/or wrist pin clearance to piston. The stiffness of the engine hot may only be barely noticeable. It sometimes doesn’t take much to consume a noticeable amount of power.

Proper wrist pin clearance is commonly overlooked on Model T’s by even some “experienced” engine builders. The piston pin bores always require at least a little line honing to align them and bring clearance into spec.

The clearance specs listed on the new piston boxes for the last several years are also too tight.

If the engine hot is absolutely as free as it was cold, then the problem likely lies in the drivetrain or rear axle.

Piston/wrist pin seizing would have been my suggestion, however you describe as std bore & stock. Iron pistons?
The next stop would be carburetor getting too lean. This could happen with carb icing without the heat pipe or the fuel level not meeting demand from fuel system reduction. You were running @ high fuel demand. As simple as the restrictive flow from as purchased Viton needle/seat units. They need modification to open their restrictive orifice.
I had a straight thru NH that required richening for hi speed running & leaning for low & idle. Constant re-adjusting. It lost power & coughed if not richened for longer hi speed use. You could try richening the mixture before that point where the motor starts loosing power as a test & put a heat pipe on if not already installed.

[John Codman]

I'll agree with the last sentence of Norm's first post. Check anything that has been done to the car since it last drove without heating issues. I would also check the coolant temperature when it starts to lose power; is it really overheating? I would think that it would have to be very near boiling for it to lose power.

[Marshall V. Daut]

Did you re-adjust the bands recently? I adjusted the Kevlar bands prior to a local Model T tour years ago to achieve better braking and after 1/2 hour or so on the way to the tour, the car began to slow down and lose power. It finally locked up and stopped in the middle of the road. It was early on a Sunday morning, so thankfully there was no traffic to hit me. I dug down to the bands and loosened the adjustments , especially the brake band, thinking it had locked up the engine as the drums and oil heated up. Sure enough! By doing that, the car was drivable again and I had no more problems for the rest of the tour. Admittedly, an odd thing to happen, but the bands (or maybe only the brake band) were just too tight, which gradually slowed down the engine and eventually stopped me cold in my tracks. Check your band adjustment.
Marshall

[speedytinc]

Not an uncommon issue for a water pump to move water too fast, not allowing the radiator to cool.
Thats why there are thermostat kits which also slow the flow by their restrictive nature once up to temp.
Of course, the faster you run, the faster the water pump moves the water.

[RadRacer203]

That could definitely be an issue with the carburetor, I haven't done anything to it yet aside from making sure the bowl and jet was clean, and adjusting it with the knob on the dash. Adjusting it while it was driving didn't really change anything, so it seemed to be set correctly, but I guess it could be icing, my heat shroud thing, whatever it's called, was in bad shaoe and I removed it for the moment and haven't gotten a replacement yet. Also, I don't know if this is a carb issue or an exhaust pipe issue, but it does tend to pop out the exhaust out of sync with the engine, especially at idle. The engine is running fine, and at an even rpm but it just sorta pops. Probably an exhaust leak is my guess with that though.

I very much doubt there's an issue with the engine like wrist pin clearance or a bent rod or something, as far as I can tell this engine has never been apart more than the valves and head. If there's any internal damage it will probably have been caused by this latest issue.

I will definitely check the temperature with an accurate thermometer if I don't find a smoking gun like a seized water pump. Was planning on descaling the block and flushing the radiator really well when I changed the coolant in the spring.

That's a very good call with the band adjustment, I will absolutely recheck that. It just got new kevlar bands, and I thought it was all adjusted correctly, but maybe I was wrong

[speedytinc]

"just got new kevlar bands"
Did you remove the HH to install them?
Out of round kevlar bands will be a constant source of friction & heat, even when adjusted "properly"

That popping is an indicator of a lean miss. Try putting the carb stove pipe back on.
Did you check the intake manifold for ice @ the 90 degree bend?

[RadRacer203]

Ok I'll double check all that when I get back to it Saturday. I need to find a replacement for that carb heater thing still, the one on it isn't usable anymore. What do you mean by HH?

[speedytinc]

Ok I'll double check all that when I get back to it Saturday. I need to find a replacement for that carb heater thing still, the one on it isn't usable anymore. What do you mean by HH?

Hogs Head.

Even if you have to wire the heat pipe on, its use will help in your problem diagnostics.

[Norman Kling]

The Hogs head is the top part of the transmission case above the crankcase. It is the top half with the pedals. You need to remove it to replace the bands with Kevlar. If you try to put them down through the inspection plate at the top of the hogs head, you risk twisting the bands which will cause uneven clearance with the drums so that even when they are loose enough to allow the drums to turn, they will have an area of binding where they are twisted.
Concerning the valve job. If the lifters are original type, the adjustment is made by grinding the stem to get the proper clearance. If they are the more modern adjustable type, you need to adjust the clearance. If the valve does not close completely, you might be burning some fuel in the exhaust manifold causing the popping. This could also occur with a rich mixture.
Norm

[RadRacer203]

Ok, I did take the hogs head off when I replaced the bands. I'm certain I didn't bend them out of shape when I did that. I may have the brake band adjusted too tight though, I dunno.

I'll be checking the valve lash for sure, should be around .015 ish right?

[Jerry VanOoteghem]

Not an uncommon issue for a water pump to move water too fast, not allowing the radiator to cool.
Thats why there are thermostat kits which also slow the flow by their restrictive nature once up to temp.
Of course, the faster you run, the faster the water pump moves the water.

This theory always neglects the notion that if the water moves too fast to cool in the radiator, it's also moving too fast to heat in the engine.

[RadRacer203]

Ok, working on the '26 again trying to figure this out. Looks like my water pump and fan are fine, I'm a bit low on coolant cause I didn't tighten a hose clamp enough, the carburetor was a bit lean and also icing over so I definitely need that intake heater thing, whatever it's called. Going to check the transmission bands now once it cools off a bit, but I think the brake band is adjusted too tight

[TXGOAT2]

Valves adjusted too tight may fail to seat once the engine warms up.
It would be a good thing to have someone with T experience examine and drive your car and discuss the issue(s) you're having with it.
If the head was removed and replaced and the head bolts were not properly checked out, and torqued, and re-torqued at that time, I'd be very concerned about a head gasket leak or leaks. It's possible for the head gasket to leak without leaking any water. A single head gasket leak can result in low compression in two adjacent cylinders.

[RadRacer203]

I'll retorque the head when it's good enough weather next, and check the valves if it happens again, but between the brake and clutch bands, fan, coolant, and mixture I think I probably fixed it. I think I have an exhaust leak is why it's popping, but it's definitely doing it a lot less now. Gonna put a wanted ad up on here when I get home for the carb heater shroud

[RajoRacer]

They're called a hot air pipe & if you have the stock combination choke/mixture rod, you'll need the correct one with the indent for the rod to clear.

[RadRacer203]

They're called a hot air pipe & if you have the stock combination choke/mixture rod, you'll need the correct one with the indent for the rod to clear.

Got it, thanks. Yeah I was gonna order a repop but Lang's seems to only have the '25 and back one but I need a '26-27

[jab35]

Michael: You've probably checked EBay, here's one listed as fitting thru '27, that appears similar to the Lang's photo but a little spendy in my opinion. Lang's do have many used parts that aren't in the catalog, I suggest a call to see if they might have something that would work.

https://www.ebay.com/sch/i.html?_from=R ... sacat=6000

I have nothing to do with that product or seller.
My '26 coup had standard NH carb and an aftermarket cast aluminum hot air stove, which is irrelevant to your search, but I mention b/c there might be some used aftermarket ones that would suit your needs. Best, jb

[RajoRacer]

Here's what hot air pipe you'll need - notice the flattened are and the manifold clamp connection. I'll check my stash.

[RadRacer203]

Here's what hot air pipe you'll need - notice the flattened are and the manifold clamp connection. I'll check my stash.

Yeah, that's definitely the one I need, looks like like the one I had except not cracked in like 4 places!

[Allan]

Michael, just a tip on adjusting kevlar bands. They should be as loose as possible, so you have the maximum gap between the band and the drum.
Find a nice flat spot and back off the bands. Then re-adjust just enough for the bands to work as they should. Drive the car to check this. If they slip still adjust a little more, until they do as they should. Then check their action on a hill. You may need a little more adjustment. Once you have them working properly, resist the temptation to give them a little more so you don't have to come back to them again.

You will have to repeat the above procedure three or four times until the bands have settled in, but once settled, you will rarely have to adjust them again.

Allan from down under.

[TXGOAT2]

With Kevlar bands, any of the 3 pedals should go down to within 1 1/2 inches of the floorboard... or a little less ... when pushed down firmly using your foot. No pedal should ** touch the floor board when pressed firmly, but any of them will be closer to the floor than is usual with modern vehicles when pressed firmly.

The linkage must be in good condition and adjusted correctly to get good results.

[Allan]

Measuring pedal travel in relation to floorboard slots is not a reliable indication of adjustment. It presumes the ramps and notches on the pedals are like new, the drums are not worn, the pedal slots in the floorboards have not been modified, and the pedals are not bent after a 100 years of use. It may be a good place to start, but the above variables are likely to add considerable variation to pedal position when the bands are adjusted to operate as they should. This variation from "normal" is likely to cause concern, especially with a newbie T owner.

Allan from down under.

[RadRacer203]

My bands definitely were too tight before, except the reverse one. The brake band might still be slightly tight, but I got it as loose as I could while having a slight amount of tension on the spring so the nut can't back off. I think the spring for that band specifically should probably be replaced, and I'm going to do that soon. I think I got them adjusted correctly now, but I've got a set of wrenches in the car anyway

[TXGOAT2]

I'd replace all of the springs or shim them as needed.

[TXGOAT2]

"Measuring pedal travel in relation to floorboard...."

My point is that you DO NOT want a "high" pedal like you would want in most all conventional vehicles, especially if you are using Kevlar bands.

Satisfactory performance depends upon linkages being in good condition and linkage adjustments to be correct.

Bent, broken, or well-worn parts will not function as they should.

[Charlie B in N.J.]

Do nothing until you get that heat shield on the carb. I'm obviously with the "It's a fuel problem" guys.

[RadRacer203]

Ok, got a chance to drive it again today, and I definitely solved the overheating problem. No losing power after a long drive. Still has the squeak, which I'm certain is the water pump, I'm going to install zerk fittings because I don't think the grease cups are working especially well. Only issue I had was poor running after a while which was definitely the carburetor icing over. The new hot air tube should fix that, but it hasn't come in the mail yet. I also retorqued the head after the drive, so that is definitely all sorted out now. Aside from needing to change the coolant at some point, it's ready for the road again!

[RadRacer203]

Finally had a beautiful day, and I got the T home from the shop today. Got the new hot air tube on (thanks Steve!) and took it for a longer drive. That hot air pipe definitely made a difference, but I think the carb is still behaving a little weird. Once the engine gets nice and hot I have to turn the knob on the dash to lean out the mix, but when I go to idle, it's definitely running too lean and popping out the exhaust a bit. I haven't gone through the carb totally yet, but what should I check out when I do have it apart? I've done lots of outboard motors, lawnmowers, a few motorcycles, but not one quite like this before

[speedytinc]

Carb fuel level is too low. Re-adjust your float.

[RadRacer203]

Ok, I'll check that today. Should the float be basically level when the needle and seat are closed?

[speedytinc]

Ok, I'll check that today. Should the float be basically level when the needle and seat are closed?

Check your service manual for the exact spec. Just under 1/4"
Its a starting point. When the FUEL LEVEL is set correctly the carb will run @ its best for hi speed & idle with no need to richen or lean the mixture.

[jab35]

Check also for restricted carb idle mixture passages if correcting the float level does not correct idle situation. jb

[RadRacer203]

Ok, got the carb apart, and I definitely found a few things. I apparently need to drain my sediment bowl cause there was a very small amount of water in the bottom of the carb, probably just condensation cause the weather is so strange here. The float was adjusted a bit too low so I fixed that, and I don't know if it was original, but the inside was painted, and it was flaking off. Got it all clean and made sure all the passages are clear, just ordered a gasket kit from Lang's cause I tore the original bowl gasket, and a new needle because it has a pretty deep groove in it. The needle and seat was apparently replaced with a ball type one, and that has been working amazing so I'm leaving that alone

[TRDxB2]

Ok, got the carb apart, and I definitely found a few things. I apparently need to drain my sediment bowl cause there was a very small amount of water in the bottom of the carb, probably just condensation cause the weather is so strange here. The float was adjusted a bit too low so I fixed that, and I don't know if it was original, but the inside was painted, and it was flaking off. Got it all clean and made sure all the passages are clear, just ordered a gasket kit from Lang's cause I tore the original bowl gasket, and a new needle because it has a pretty deep groove in it. The needle and seat was apparently replaced with a ball type one, and that has been working amazing so I'm leaving that alone

You should drain a sample of fuel from you gas tank just to make sure it wasn't the source of the water (condensation).

[Jerry VanOoteghem]

The needle and seat was apparently replaced with a ball type one, and that has been working amazing so I'm leaving that alone

Has it really been working amazing? Some of the symptons you describe are often attributed to those ball seats, (a.k.a. Grose Jets). Just because it's not leaking, it does not mean that it's letting fuel flow freely enough into the bowl. It would be best to get Scott Conger's excellent needle & seat that allows for greater fuel flow than even the stock Ford seat.

[speedytinc]

The needle and seat was apparently replaced with a ball type one, and that has been working amazing so I'm leaving that alone

Has it really been working amazing? Some of the symptons you describe are often attributed to those ball seats, (a.k.a. Grose Jets). Just because it's not leaking, it does not mean that it's letting fuel flow freely enough into the bowl. It would be best to get Scott Conger's excellent needle & seat that allows for greater fuel flow than even the stock Ford seat.

I second this. Those gross jet balls will typically get sticky & stay open or closed randomly.
If you are going to drive it, carry a viaton unit with you at the least & the tools to replace it.
Smartest move is to change it out now.

[RadRacer203]

Ok, I'll grab a new needle and seat too, might as well since they're cheap. If it doesn’t help I'll just keep the ball type one as a spare

[speedytinc]

The off the shelf units are too restrictive. Wont flow as much fuel as the originals did.
Get a hi volume unit from Scott Conger.

[RadRacer203]

Got it, I asked him about it. Still gonna get the normal viton one, probably just keep it as a spare and get rid of the ball type one if it's really as bad as everyone is saying

[Moxie26]

If, as was said, the Grosse-Jet valve balls get sticky and stay open or closed,...... it does so from the gunk that's in the gas tank , line, and sediment bowl. Just a personal observation... I've used that style valve in my carburetor the past 25 years and never had a problem.... Guess I never had gunk in my fuel system before. ...... The gas tank you have is mounted in the cowl,... the same in my '26 runabout.

[RadRacer203]

Ok, got the carb back together with a new Viton needle and seat, mixture needle from Lang's, and a gasket kit! And it runs worse than before... I'm stumped now. Triple checked everything, and I can't find anything wrong. Does anyone offer a rebuild service for the Holley NH? I think at this point I just want it gone over by someone who knows what they're doing since I can't seem to get it. I do know it has to be the carburetor though, I have no vacuum leaks, compression is good, I'm getting good clean fuel flow to the carb, and the ignition system is pretty much all new and double checked. Before it ran poorly at idle but good in low and high, now it runs poorly and has no power at idle, low gear, and high gear.

[600wt]

If only.....there is a Model T owner in your neck-of-the-woods, who is running the same carb as you (and his runs good), and the owner would be willing to unbolt his and come bolt it to your motor, as a trial for a test drive.
There is nothing as good as replacing a bad part with a "known-good-part" to see if the bad carb is actually the problem.

[RadRacer203]

Good news! I finally figured out my running issue. Turns out it was a combination of carburetor, the timer being very iffy, and one of the spark plug wires arcing on the coil box bracket. Just have to figure out why the generator isn't charging now

[RadRacer203]

[RVA23T]

Totally based off the pic above it stops going in the cold also

[RadRacer203]

Surprisingly it doesn't mind the cold much at all! Takes a couple tries to start but runs great afterwards. It doesn't do very well in the mud though, I wish they still sold offroad style tires in this size, but I could only find ones with regular road tread