b7100 HST overheating

[Eugene23]

My 95 b7100 with 800 hours seems to run fine, although it has thrown steam many times.
I did the radiator test with radiator cap removed. The fluid level goes up and down and the bubbles do escape from the top at a random rate, on and off bursts.
The tractor seems to lose coolant rapidly when mowing with my 4' rotary cutter; seems like a blown head gasket? However, the tractor starts and runs fine and the oil appears to be the normal black (not milky) color.
I would appreciate suggestions as to what to do next.

 

[D2Cat]

Use an infrared heat gun to check temp at upper and lower radiator hose. Differential will tell if radiator is doing it's job. Might use something like purple power cleaner to spray on radiator fins and let set for a while before washing off with a garden hose. Often time dust becomes mud and sticks to the fins reducing cooling capacity.

 

[My Barn]

Radiator could be plugged-up...I would flush it and the block too! D2Cat is giving a good way of checking it out.
Or the coolant might need to be change and fresh Anti-Freeze put in? Have you cleaned the screen in front the radiator.

 

[North Idaho Wolfman]

Your getting bubbles in the radiator right?
If you are you have a cracked head.

 

[6869704x4]

You got a radiator pressure tester?

 

[Eugene23]

No pressure tester, but I did replace the radiator cap a few yeas ago. Radiator kind of 'burps' with cap off. fluid rises up and then drops. Again, oil looks fine, not milky. I will be working on it off and on as time permits. Thanks for the replies.

 

[07wingnut]

Your getting bubbles in the radiator right?
If you are you have a cracked head.

Interesting diagnosis. Could you explain why you suspect a cracked head as opposed to a leak thru the head gasket?

 

[North Idaho Wolfman]

Interesting diagnosis. Could you explain why you suspect a cracked head as opposed to a leak thru the head gasket?

I'm really just playing the odds, I've seen or heard of heads cracking about 1000 to 1 on leaking gaskets.
Normally If it's a leaking head gasket it will fill the cylinder with coolant, where a cracked head has a 50/50 chance of doing it or not.
Because the head crack can be higher than radiator and fluid level and expands when hot, and the head gasket is lower on the radiator and isn't normally effected by temp.
But hey I would love to be proven wrong, it's the same work to check for both.

 

[Eugene23]

I did the temperature test on the radiator today. The top of the radiator got to over 200 degrees while bottom temperature were 120 or 130. This is all with no load on the tractor. FWIW, it only seems to overheat when mowing thick pasture grass.

 

[Vigo]

I have a temp sensor on my upper radiator hose outlet and it only hits 180+ under heavy load for several minutes straight. It will NEVER hit 200 if idling or lightly loaded.

It seems like you have a combustion leak into the cooling system. The fluid level rising and lowering is probably because a gas pocket is forced into the cooling system which displaces an equal amount of water and causes fluid level to rise, but as air bubble reaches the upper radiator tank and 'purges' to the air, the fluid returns to its previous level. If you had a cooling system pressure tester you would actually see this on the pressure gauge, plus the general non-conformity of pressure rising 'out of step' with coolant temp rise. Generally the pressure would only rise slowly in conjunction with coolant temp, but never rapidly or spiking, unless combustion leaks into cooling system.

Regardless of what's causing it you have to take the head off to properly fix it.

 

[D2Cat]

Here's a product I'd recommend. Look up the history of the company and get some feedback. It goes to the leak because it's in the radiator fluid and then the heat creates the seal.

https://www.amazon.com/Pack-Irontit...hvlocphy=&hvtargid=pla-4583451676561043&psc=1

 

[200mph]

Can always check for combustion gases using something like this.

Combustion Leak Detector (harborfreight.com)

I think autozone or advance auto rents this equipment but need to buy the fluid.

 

[07wingnut]

I'm really just playing the odds, I've seen or heard of heads cracking about 1000 to 1 on leaking gaskets.
Normally If it's a leaking head gasket it will fill the cylinder with coolant, where a cracked head has a 50/50 chance of doing it or not.
Because the head crack can be higher than radiator and fluid level and expands when hot, and the head gasket is lower on the radiator and isn't normally effected by temp.
But hey I would love to be proven wrong, it's the same work to check for both.

Thanks for the explanation. Experience counts for a lot when diagnosing this kind of stuff.