MTFCA Forum

Subject: Has anyone added a vent to a Roof-8 OHV head to fix overheating?

Hi all — I’m running a 1927 Model T engine with a Roof-8 OHV conversion and an added water pump. After about 10 minutes of running, I get water and steam overspilling from the radiator. What’s odd is that the radiator itself isn’t overheating — the bottom tank stays at normal temperature.

I’ve been advised to add a vent on or around the Roof head to relieve trapped pressure/heat, and before I start modifying, I’d love to hear from anyone who has actually done this.

If you have:
• Where exactly did you place the vent (breather cap, hole in valve cover/head, draught tube, etc.)?
• What size/type of vent (threaded breather, small fitting, etc.)?
• Did you notice any side effects (oil carryover, loss of pressure, etc.)?
• Most importantly — did it actually stop the overspilling/steam issue?

Photos or diagrams would be fantastic. Thanks in advance!

Check the radiator- is it an old original?? Most likely the head is not the problem but an old radiator that can't transfer heat from the tubes to the fins properly.

If the pump flows more than the radiator can handle.......

If your engine is actually boiling and the lower radiator tank is cool, you either have a very clogged radiator or a water pump that isn't working. Other possibilities are a lower radiator hose that is collapsing under suction, or a thermostat, if one is present, that is not opening. If there is a thermostat present, it needs a bleeder hole to allow air to escape when filling the system with water. A thermostat that is installed upside down may not open when it should, or it may not open at all. Your cooling system should hold about three gallons of coolant, or a little more.

A hot engine with a cool radiator indicates a circulation problem, or not enough coolant. Most any older model system will vent air as coolant is added, except in cases where a modern thermostat has been added. A closed thermostat can trap a lot of air in the block and head if it lacks a bleeder hole. I don't know if the conversion OHV head can work well as a thermosyphon system the way the stock systems do. They may require a working water pump.

Your problem would sujest air trapped in the back of the Roof Overhead and /or a water pump pumping to fast. The first thing I would try is to drain cooling system and refill with the car’s front end jacked up at least 12 -18 inches, fill radiator with enough coolant to cover the tubes. Let car down and go for a 15-20 minute test drive. If problem continues or returns over time I would try installing a restrictor to slightly slow the coolant down entering the head , or removing the water pump and going stock Ford and see what happens.

A couple questions;

Which Roof 8 head…? 1 or 2 intake ports. The 1 port head has a far more open water passages and would no doubt cool better.

Which water pump…? Only about a thousand options here, and some were no more effective than adding snake oil to a stock system.

I have to agree with the above response, sounds like a circulation problem. Has the radiator been checked for obstructions? Have you tested that the pump actually pumps? Did it cool properly before something changed?

Not a Roof head, but had a rear cylinder heating issue on my ol flathead motor, even with a water pump. Heat seemed to accumulate under the ports at the rear of the block and would cause the rear pistons to stick. When I swapped an Akron-Hed onto the engine a couple years ago, I decided to be proactive about cooling. I found a water pump that actually pumped, added a port to extract some coolant, and routed a line to a Fronty water manifold on the opposite side of the engine. The Fronty water manifold injects water into the 3 freeze plugs on the port side of the engine, I left the center port blocked, and drilled a 3/8” hole to stimulate flow to the front and rear. No more hot cylinders!

Could it be a head gasket backwards issue?

... Or a head gasket leak... Or water pump sucking air at the seal...

Your radiator is not flowing freely enough.

Have you tried machining the head to allow free flow into it... Yes, this roof was machined a bit much.

^^^^^^^^^^

Still looks more usable than mine!

Its cracked between the valves. My grandfather was making valve seats but when mom would get it hot the head would expand and the seats would pop out. Along with the car I got a rather large collection of trouble trophies.

Thanks for all the usefully tips.
The Roof 8 head is a 2 port intake ( only 1 updraft carb) The pump is a new Texas T pump.
No collapse of the pump intake tube.
Same issue before I installed the pump. Even worse.
How can I best test the radiator. It is an older V-shape honeycomb one.

To check for plugs you could rig a pump to pump in and out on a closed loop. Place a low pressure gage on each end and look for a pressure drop. This will help to check for flow but not heat transfer.

The issue with honeycomb radiators is that you cannot rod them out.
Take off the radiator and use a hose in the top to watch the flow out. If it backs up easily there is the issue.