TO-30 Boil Over

graham_in_NJ · May 2, 2020

Recently had to have my radiator repaired for a few small leaks. Cost me the price of a new aftermarket, but often the overseas stuff is absolute crap. While I was replacing the radiator, I found that there was no thermostat in the upper hose, so decided it would be good to get the thing to work at the correct operating temp after reading some of the archive posts. After running about 20 minutes, it boiled over. Super. I took the t-stat out and checked the opening temperature in a pan of water. After a few repeated tests, it's opening at 190 degrees. If I'm not mistaken, it should open at 160, correct?

Steve@Advance · May 2, 2020

When doing the pan of water test, you have to watch very closely to see when the thermostat just starts to open.

That is more the set point than when it is fully open, which may not happen until it is near 190.

Still that is below boiling, so by the time it was actually boiling hot the thermostat would have been fully open.

Most thermostats have a small bypass hole or a v notch in the disc to let "some" water and any air trapped below escape. If there is no vent, try drilling a 1/16" hole to allow some bypass. The bulb needs to be submerged in coolant to respond correctly. It also needs to be down close to the outlet neck.

Some other possibilities...

When you filled the coolant, did you let it run up to temperature so the thermostat was open and the system was full?

When the radiator was leaking, did the engine get overheated? There could be a head gasket problem. Could have been from sometime in the past if you are not the long time owner. Sometimes the thermostat is removed to compensate for a minor head gasket leak. Many times a leaking head gasket will mimic boiling when combustion gasses are entering the water jacket. There can be coolant pushed up and out when the engine is still below the boiling point.

And there is the possibility the thermostat is defective, but it did open...

graham_in_NJ · May 2, 2020

Thanks Steve. No OH issues prior to the radiator repair. I did watch to see the thermostat (in the pan) at the beginning stages opening at 190, so 190 was the starting point.

I admit the cap was loose, but reading other posts told me that that was ok. I prefer not to have any pressure in this old radiator, even after repair and pressure test. But even so, without the t-stat with a loose cap, never had an issue. I had installed a temp gauge while the radiator was out, and right at boil-over the gauge showed at the very edge of hot (red). Cheap gauge, so accuracy is not part of the equasion. When I initailly started it, it took a while (20 minutes) before the boil over. Tractor was idling at the time, so no load on the engine at all. I wasn't watching the gauge at the time, just looked at it when the thing was puking and shutting it off.

No noticable bleed hole, although the t-stat when closed allows water to seep past at a fair rate, so I think that would allow any air to escape. Don't want to drill a hole in case I have to return it.

Going to run it today without the t-stat to see if there are any new issues.

So I guess a t-stat that starts to open at 190 is a little off if you ask me.....

Bruce(OR) · May 2, 2020

My 2 cents for what it's worth.
Stats can open from 160 to 195 depending on which one you have.
I cross referenced a stat and found it cheaper when looking for an automotive, rather than tractor, application.
Drilling a hole in a stat is cheap insurance. That blown head gasket might not be so cheap. Choice is yours.
Rad should run just over the cooling fins unless you add an overflow jug with the 4 PSI cap.
Good luck finding a 4 PSI cap.

graham_in_NJ · May 2, 2020

I agree, sometimes the tractor "version" is far more expensive. However, not sure where to find an in-hose thermostat. The parts stores these days are fairly useless when it comes to interchange. If it's not in the computer, it doesn't exist. I remember years ago when I worked in auto parts, many times we didn't even need to look stuff up. We knew what it was when we saw it and we knew what options they had if the exact p/n wasn't in stock. Anyone remember clocking alternators?

I think with my thermostat opening up at 30 degrees higher than it should presents a real problem. It's a little late. Ususlly when I buy a thermostat (except in this case - duh) I test them. I rarely find one out of spec in the automotive world. I did find two in a row that didn't open at all though. Past experience tells me that they should be fully open a few degrees past the set point. Plus or minus.

Totally lost faith in the overseas crap.

rvirgil_KS · May 3, 2020

This site has them listed under parts in left column

NAPA shows one BK S68313 160 degree

Same thermostat for several Ferguson T series and Ford N series.

Is the thermostat installed in the correct direction, and down near the block end of hose?
Overfilling radiator can cause coolant to push out the overflow
I drill small weep hole as others have mentioned. After refilling I let the engine warm up to get the thermostat open and then run for awhile with cap loose to allow any trapped air to burp out of the system.

54FergieTO30 · May 3, 2020

(quoted from post at 07:08:43 05/02/20) When doing the pan of water test, you have to watch very closely to see when the thermostat just starts to open.

That is more the set point than when it is fully open, which may not happen until it is near 190.

Still that is below boiling, so by the time it was actually boiling hot the thermostat would have been fully open.

Most thermostats have a small bypass hole or a v notch in the disc to let "some" water and any air trapped below escape. If there is no vent, try drilling a 1/16" hole to allow some bypass. The bulb needs to be submerged in coolant to respond correctly. It also needs to be down close to the outlet neck.

Some other possibilities...

When you filled the coolant, did you let it run up to temperature so the thermostat was open and the system was full?

When the radiator was leaking, did the engine get overheated? There could be a head gasket problem. Could have been from sometime in the past if you are not the long time owner. Sometimes the thermostat is removed to compensate for a minor head gasket leak. Many times a leaking head gasket will mimic boiling when combustion gasses are entering the water jacket. There can be coolant pushed up and out when the engine is still below the boiling point.

And there is the possibility the thermostat is defective, but it did open...

Exactly right on the bypass. Mine had issues too before i drilled the small hole to let some water through.

graham_in_NJ · May 3, 2020

All good info. I'll get a replacement for this one and test it. If it's closer to the 160, I'll drill the hole and try again. If the thermostat's is starting to open at 190, then it's just wrong.

TO-30 Boil Over

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