Heritage Posted March 3, 2015 Share Posted March 3, 2015 Just picked up a 91 dump truck that has been sitting a while. After about 10 seconds of running, it started leaking coolant from the resevoir cap. Shut the engine down and upon removal of the cap, the system spewed about 1/2 gallon of fluid under high pressure. Engine was stone cold. Any help trouble shooting this would be appreciated. Engine is an EM7-300. Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/ Share on other sites More sharing options...
Gmerrill0516 Posted March 3, 2015 Share Posted March 3, 2015 I'm only guessing but would it be a head, head gasket or some other means where compressed combustion gasses are heading for the cooling system? It doesn't sound good...Oil cooler internal leak maybe but you should see cross contamination I would think with coolant in the oil or oil in the coolant. Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281357 Share on other sites More sharing options...
Dirtymilkman Posted March 3, 2015 Share Posted March 3, 2015 I just had this happen to me.......your air compressor is shot. Pull the line going to your air dryer, its probably full of antifreeze Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281363 Share on other sites More sharing options...
Dirtymilkman Posted March 3, 2015 Share Posted March 3, 2015 Be sure to rebuild the air dryer too Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281364 Share on other sites More sharing options...
Heritage Posted March 4, 2015 Author Share Posted March 4, 2015 Thanks for the replies. No oil/coolant contamination visible on the dip stick or in the coolant. Will follow up on the air compressor suggestion. Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281402 Share on other sites More sharing options...
turckster Posted March 4, 2015 Share Posted March 4, 2015 When you see this happen it is one of two things, combustion into the cooling system or blown air comp. head gasket. A bad air comp. can leak air into the cooling system and not push coolant into the air system. Only sure way is to isolate the air comp. from the engine cooling system. Remove the air comp. coolant lines and plug the fittings, refill the engine with water/coolant and run the engine, if the cooling system builds pressure like before then your problem is a head or gasket. If not, air compressor is at fault. Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281426 Share on other sites More sharing options...
mrsmackpaul Posted March 4, 2015 Share Posted March 4, 2015 I have a question if the compressor was building pressure would the temp not rise and if it was building pressure thru the head wouldnt the temp rise??? dont know if that makes sense I might try and put that another way if the head was leaking it would I think be pushing fire from the cylinder back up into the water jacket and the water would heat really quick maybe ??If it was from the compressor the air would be cold getting pushed into the water would it still make heat real quick ? or would it only build pressure ?Paul Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281435 Share on other sites More sharing options...
turckster Posted March 4, 2015 Share Posted March 4, 2015 I have a question if the compressor was building pressure would the temp not rise and if it was building pressure thru the head wouldnt the temp rise??? dont know if that makes sense I might try and put that another way if the head was leaking it would I think be pushing fire from the cylinder back up into the water jacket and the water would heat really quick maybe ??If it was from the compressor the air would be cold getting pushed into the water would it still make heat real quick ? or would it only build pressure ?Paul Usually the "leak" is a hair line crack or over/under a fire ring. The majority if not all of the fire or heat from combustion is contained in the cylinder. Sometimes an engine with a cracked head will not show signs of a leak until it is at operating temps, or under a heavy load above operating temps. A cracked head is bad obviously, but combustion blowing past a fire ring will erode the steps on the liner. That is where the fire ring seals, once that is gone then the liner needs to be replaced.The radiator cap is a 10lb cap, so not that much combustion or air from a compressor is being pushed into the cooling system. I mean, its enough to push coolant past a cap but to build any heat from a leak the cooling system would have to be able to hold a lot of pressure and the leak would have to be a lot as well. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281441 Share on other sites More sharing options...
mrsmackpaul Posted March 4, 2015 Share Posted March 4, 2015 Usually the "leak" is a hair line crack or over/under a fire ring. The majority if not all of the fire or heat from combustion is contained in the cylinder. Sometimes an engine with a cracked head will not show signs of a leak until it is at operating temps, or under a heavy load above operating temps. A cracked head is bad obviously, but combustion blowing past a fire ring will erode the steps on the liner. That is where the fire ring seals, once that is gone then the liner needs to be replaced.The radiator cap is a 10lb cap, so not that much combustion or air from a compressor is being pushed into the cooling system. I mean, its enough to push coolant past a cap but to build any heat from a leak the cooling system would have to be able to hold a lot of pressure and the leak would have to be a lot as well. sounds good enough for me thanks Paul Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281449 Share on other sites More sharing options...
superdog405 Posted March 4, 2015 Share Posted March 4, 2015 Had this same problem with one of my 454's a couple months ago. Changed comp. because it was old anyway,but turned out being a cracked head. Mack reman head around $1200 for an E-7. Quote Link to comment https://www.bigmacktrucks.com/topic/39131-1991-em7-300-high-coolant-pressure/#findComment-281452 Share on other sites More sharing options...
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