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Have an issue with my 1978 Ford tractor. Engine is a 4 cylinder diesel. Had a radiator leak bad enough that I swapped the radiator out for a new one. Installed it after feeling my way through the removal and reinstall with the help of Youtube. I am not a mechanic by any stretch of the definition. The old radiator was leaking down low on the starboard side. The leak presented itself as foam. If I tried to add water with it running it would belch foam. The coolant was half green antifreeze and half water. I checked the thermostat by putting it in a pot of water on the stove. It opened and closed properly. The oil is clear with no evidence of coolant contamination. I used the tractor today in about 25F degree weather. The coolant I put in was one gallon of green antifreeze and the rest water. I moved 2 large rolls of hay and purposely ran in a lower gear than necessary to keep the RPMs up and warm up the engine. It took about 30 minutes and all together it traveled about a mile. When I finished and parked I looked and saw foam coming out of the overflow at the cap. The engine seemed unusually cool to the touch and the lower hose had no heat at all.

Do I have exhaust getting into the cooling system? As I said there is no evidence of water in the oil. If not that what is going on?

Hmmm...might be a cracked head or bad head gasket.


Did you replace the cap?

I’ll bid a $1500:

Do those Fords have thermostats ? A cool engine & foaming radiator indicates a blockage of flow from radiator to engine.

May be the water pump? or somthing pressurizing the radiator

Would not a blockage cause overheating? But yes it does have a 160F degree thermostat. I do not know at what temperature it opened when I heated the thermostat in a pot on the stove but it opened. The bottom hose was cool. I did not take off the cap when I shut it down and did not feel the top hose but the engine seemed cool to touch. My concern is that exhaust may be getting into the cooling system. The tractor runs fine. The engine was overhauled about 5 years ago and has been used about 150 hours a year since then. I change the oil every 100 hours or once a year which ever comes first. The engine has never run hot since I've owned it about 15 years. The new radiator came with a new cap.

I'd first pressure test the cap if you haven't, then warm up and use a radiator pressure tester while running. It will point to your most likely problem.

At 25 degrees, the lower radiator hose is supposed to be cold. That is where the chilled coolant returns to the engine.

But the upper hose should be warm.

Start the tractor, run it till it it is good and warm. Take radiator cap off, lay hand over top of radiator and check for gases escaping radiator.......compression leak!

If negative, I would probably do a chemical flush of cooling system to get rid of contaminants. Refill with 50/50 antifreeze/water. Pressurize system with a good radiator cap.

If you continue to get foam in the radiator, you have a compression or oil leak in the system somewhere.

If you fill it when cold and not running....and then start it with the cap off..what do you see in the radiator?


Do you have a laser temp gun?


Temp differential between top and bottom of radiator should only be 10 degrees or so.

I would lean toward exhaust pressure getting into the system but what do I know. I can change some parts if not too complicated, I'm not into diagnosing. There is no contamination of coolant in the oil unless I find it tomorrow when I pull the dipstick. And I don't know how much coolant was lost with my 30 minutes of use today.

Did you properly bleed the system after installing the new radiator and filling it?

I will start it tomorrow with the cap off and report back. With the old leaking radiator I was getting foam from the leak which was about 3 or 4 inches from the bottom.

Don't have a laser temp gun.

Probably not. Tell me how to do that.

That is most likely. Easiest to fix is a bad head gasket. Then second is a cracked head.

Unless that engine has a wet exhaust manifold gasket, which I doubt. And even then it would be more likely to see white exhaust gases than contaminated coolant from a leaky exhaust manifold gasket.

Of course, one never wants to discount head bolts or manifold bolts out of torque specs.

Take the cap off with the engine fully cold, start the engine and let it warm up until the thermostat opens. The coolant level will drop as the coolant circulates and purges air out, then top it off and install the cap.

If it was a blown head gasket the motor would get hot quick. The OP said it stayed very cool.

there should be a bleeder screw somewhere, or just a regular bolt in the top of the head with a copper washer.....just a high point in the system....take out while filling....replace when coolant runs steady. The method BeardedGunsmith mentions can work and usually does but is very problematic with 03-07 dodges and crew cab Polaris ranger, that is why they have designated bleed points that every Chrysler/polaris certified tech knows well. also if the system is ran without being purge your head is very likely full of air pockets, that is bad. you can by test kits to see if you have hydro carbons in the coolant system and that will let you know if exhaust pressure is building in the coolant system, though it is unlikely if it is not turbo charge and the exhaust has practical flow. no malice intended here.

If anything it is unusually cool. That is why I took the thermostat home to make sure it didn't stick open. Put it in a pot and it opened when the water got hot and closed when I took it out. The tractor ran cool today. I am going to try Idaho Shooter and Jim's advice and run it from a cold start without the cap on.

That tractor is needed this time of year. I have two tractors and cattle two miles apart in different pastures and a busy highway to traverse. We put hay out every other day.

I did this about noon today. Let the tractor run, and it ran nicely but foam soon started coming out the top of the radiator. I let it run for 30 to 45 minutes. Never quit foaming. So I killed it and finished securing buckling down the sheet metal and secured the air filter canister which took a while. There wasn't really much coolant gone so I topped it off, screwed down the cap which is a 19 pound pressure cap (seems a little high). I took off with a roll of hay and went the mile round trip at 2400 RPM. It put some foam out the over flow so I am sure there was 19 pounds plus of pressure. Did not remove the cap. No steam coming out of the exhaust and no contamination yet showing in the oil.

My mechanic friend that works a good bit on older tractors suspects exhaust pressure getting into the cooling system but all he knows is what I've said here plus a short video of the foaming while the tractor was running with the cap off. He suggested to put the cap on and don't let it overheat and run it and see what happens.

Have I got a head or head gasket issue? The tractor runs fine and the hoses were both cool to touch.

Fill up the rad and leave the top off overnight ya got air in it