631G
Senior Member
Last fall the D9G (SN:66A7869) that we've been running with started burping out coolant from the pressure relief cap when in operation. We thought that we were having a heating issue and because we were close to the end of the job we just brought the machine back to the shop to give it a once over.
We pulled and replaced the relief cap after finding that it was corroded. We also found a few other leaks on the cooling system we then repaired and thought we were all set. We had a new job come up and decided to put the machine back to work pushing pans. Before taking off to the job I put the machine out back to push against some dirt mounds to get it up to temp. Sure enough the relief cap starts to burp out coolant. The odd thing is that the motor was not hot, not even close to being hot. What I did notice is that the cooling system pressure gauge was showing high pressure in the system. When the pressure gauge would get up into the high side, it started to burp. I let the machine cool off and checked the coolant level and the color only to find the radiator full and that it was still green as new. I ran the machine some more and the pressure gauge would build up pressure as I ran the machine, burp a little, and then stop for a while until I really worked the machine hard with long hard pushes against the mound and cycling the motor rpm up and down like you would pushing pans. If I stopped a for a few minuets the pressure would come down to normal. At idle the machine would show normal pressure.
So here is the question is this a simple case of a bad head gasket? Could it be a bad seal on the precombustion chambers in the head? I would think that if the head gasket was blown I would see soot in the coolant and the pressure would stay elevated? I'm a little stumped here. What do you guys think?
We pulled and replaced the relief cap after finding that it was corroded. We also found a few other leaks on the cooling system we then repaired and thought we were all set. We had a new job come up and decided to put the machine back to work pushing pans. Before taking off to the job I put the machine out back to push against some dirt mounds to get it up to temp. Sure enough the relief cap starts to burp out coolant. The odd thing is that the motor was not hot, not even close to being hot. What I did notice is that the cooling system pressure gauge was showing high pressure in the system. When the pressure gauge would get up into the high side, it started to burp. I let the machine cool off and checked the coolant level and the color only to find the radiator full and that it was still green as new. I ran the machine some more and the pressure gauge would build up pressure as I ran the machine, burp a little, and then stop for a while until I really worked the machine hard with long hard pushes against the mound and cycling the motor rpm up and down like you would pushing pans. If I stopped a for a few minuets the pressure would come down to normal. At idle the machine would show normal pressure.
So here is the question is this a simple case of a bad head gasket? Could it be a bad seal on the precombustion chambers in the head? I would think that if the head gasket was blown I would see soot in the coolant and the pressure would stay elevated? I'm a little stumped here. What do you guys think?