QuestionI have a 1928 Model A that I recently restored. Went on my first outing last Saturday and it overheated twice. The temperature was in the 60's and we were driving but about 40mph when the first occurred. I was running with 50/50 antifreeze. We added water and it was ok until I was heading for home. Was probably running a little faster than 40 (my speedometer wasn't working), and it overheated violently. The temperature was less than 60.
The flow test on the radiator indicates it is draining properly. Timing appears to be correct-getting point opening on 1st or 2nd detent from the top.
I did have a rear brake dragging on the trip.
I was told to clean the radiator and engine with two gallons of vinegar and top off with water. Run it and let it sit for two weeks. Ever heard of that? I haven't completed that yet.
I was running the GAV on the lean side. My understaning is that will cause overheat.
I am getting some brown staining on the engine from the head gasket down, but it doesn't appear to be rust. It's too difficult to remove.
My compression test (cold) indicated 64-68 psi.
Do you think I have a head gasket problem or a radiator heat transfer problem.
The radiator was cleaned (I'm not sure how well since someone else did it before I bought the vehicle).
The radiator was painted with a gray paint when I bought the vehicle. I painted over the gray paint with black radiator paint from Eastwood. Do you think the gray paint is causing a heat transfer problem and will a radiator shop be able to remove it??
Any other suggestions would be appreciated.
Thanks.
In case you would like to contact me, I'm at
AnswerI wrote a paper on this some time ago. I'll give you the short version of it. You very likely have a plugged radiator. The simple flow test does nothing. The rad needs to be rodded out. Boiling out will not work. Do this, take off the upper hose from the rad and put an old sock over the rad inlet with enough slack to catch junk floating around in there. Put the hose back on and run the engine for a few minutes at high rpm. Check the sock and see if it caught any junk. Remove it and know pretty sure that there is no more junk running around in there. You Can do this now or later, but be sure you do the sock trick before you put on a new radiator, assuming you can't get anyone to rod out your old one. They are hard to work on. That's the only answer on the rad.
Now, before you do any of that, retorque all the head bolts. You could have combustion gases getting into the water jacket. In third gear and low speed, try to accelerate with the rad cap off and try to see if you get any bubbles out of the rad. top tank.
Don't worry about your carb mixture. It can cause more heat rejection, but that is not your prob. I'll look for my old write up and attach if I find it.
The key is to be able to drive 45mph for ten minutes. If it does not overheat, your system is good. A lot of cars, A's, can't do this.
Good luck and let me know how you make out.
I'll attach that paper on a different answer to you later.
Good luck
Jack
Leon, here is that write up on the rad. jack
Comments on the Model “A” Cooling System
All of us have had cooling problems with our cars, and there have been many attempts at fixes for the problem. I want to point out a few facts and thoughts at what we might consider as we approach the problem.
Basically, the A system is a pull (suck) through system. Not the best way to design a cooling system, but it will have to do. All systems have internal hot spots where the coolant flashes into steam. In most cases, it condenses back into a liquid as soon as it travels within the water jacket and hits some cooler water. This is normal. With a pull through system, if the radiator is plugged to some degree, and I think most are plugged, as the pump tries to pull the water out of the radiator, it results in a lower pressure within the engine and head. This is in the wrong direction. As the pressure decreases, so does the boiling point. I have not been able to measure this lower pressure. I have thoughts on how I might do it, but have not yet had the chance.
It has been said many times that the pump pumps more water than the radiator can handle. This is impossible. The pump gets all of its water from the bottom of the radiator. That is all it can pump. I do think the A pump is oversized for the job, so it is very aggressive in trying to get the water out of the engine. That’s why we have such a low pressure in the water jacket.
Many of us have cut down the size of the impeller on the pump. This is in the right direction since it reduces the size of the pump, and this reduces its ability to draw that low pressure in the engine. Just doing that has “fixed” many systems.
What I think happens within the engine when we are going about 45 mph on a warm day is the following: The radiator is plugged to some degree. The pump works hard and lowers the boiling point to where the hot spots within the engine flash large amounts of water into steam creating a large bubble. When this happens, the pump is free to pump the water that is down stream of this bubble, out of the engine. The bubble simply expands to fill the void. At this point, the pump is pumping more water than the radiator can handle. The pump is pulling on that bubble and trying to pump all of the water out of the engine, independent of what is coming through the radiator. When this happens, it causes the water to escape out of the overflow tube and anywhere else it can get out. This progresses until you are making a lot of steam in the engine and it all goes down hill from there. If you check early enough, you will see the familiar foam in the top of the radiator. This is caused by the big bubble of steam and water (antifreeze) being whipped into a foam by the pump.
How to fix all of this is simple. Get the radiator unplugged. The lower the restriction of the radiator, the less affect the pump will have on creating the low pressure within the engine.
Our current new radiators that we buy have the small more efficient tubes in them. When they re-core a radiator, they do it with those very small tubes. The old A radiator had the big tubes that let the junk flow through.
I put a new radiator on my car, and after a few miles, it plugged. I paid $400 for a filter.
The old trick of filling up a radiator with water and letting it flow out does not tell you if the tubes are clear. This is a very poor measure of how open the tubes are. I have been working on a method to “flow “a radiator, but I have not perfected it yet. A full flowing radiator needs a large water supply to keep things at a steady state while you measure the flow. I can come close, but can only measure a radiator that is partially plugged.
What we need is someone to re-core our radiators with a large tube core.
If you think you have a plugged radiator, or someone in your club does, try to hook up a clear vinyl tube to the drain petcock, or a fitting in that same area, and run the tube up outside of the hood, above the top of the radiator, and where you can see it. Have someone hold it there while you run the engine at an rpm that equates to 45 mph. With the engine off, the water level in the tube is the same as the level in the top tank. With the engine running at 45 mph, I predict that the level in the tube will surprise you. I have not been able to do this, but I think the level in the tube will go so low that it might even suck air into the petcock. I would then like to do this same set up on a car that does not overheat, and compare the results.
If you can find the time and energy to do this, please let me know.
Jack Bahm
Oakleaf Region
