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help diagnosing possible blown head gasket

  • Thread starter **DONOTDELETE**
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**DONOTDELETE**

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ok, here's the deal. got low compression in 4 and 6. manual says when two side by side cylinders have low comp. there is a good chance of a blown head gasket. says to look for antifreeze in the oil. well, i can't tell by looking at the oil if there is any antifreeze in there (looks black as always /forums/images/icons/tongue.gif ) but when i opened up the radiator cap i noticed i was low. i have no coolent leaks and a brand new radiator. is there any other way to diagnose this. if all i have to do is replace the head gasket then that's great. just don't wand to tear it all apart and find bad valves/guides etc and have my work truck down. i have a spare set of heads to rebuild but wont if i don't have to. wadda yall think bout this one?
 
You need to check the head with a straight edge to see if there is any warpage and check the block( but highly doughtful its the block) look at the gasket carefully for blow by between the cylinders could reflect burtn on the sealing rings of the gasket, water/or oil. also check for cracks in the head(between the valves,spark plug hole,etc..... CHeck it all! If the head is warped take it to a machine shop and have it surfaced before you replace the gasket! If its cracked hit the bone yards or buy a new Hi-perf set.
Bill C
 
Hey jason check to see if your spark plugs have any sign of water on the tips of them .
colin
 
Sounds like what happend to mine. The coolant was getting burnt out the exhaust so it never got in the oil. Found out i had a very small crack in two cylinders. That was after i replaced the heads and gaskets thinking a gasket was bad.
 
now i'm getting depressed. wish i could afford one of those ram jet thingies /forums/images/icons/tongue.gif
 
If you blew a gasket between the cylenders then not only would they be abnormally low, but usually be within 5 psi of each other. Look for white foam on your oil filler cap, or the same ijn your radiator tank... sometimes with the radiator full and the cap off, you can run the truck and see lots of bubbles. A little bit of bubbling is normal as well as it overflowing with revving the engine. Spark plugs should be an additional sign that something is up. Same with a regular stumbling idle.
 
first off i had my cylinders flip fopped. 3 and 5 not 4 and 6. anyway, here's what i got:

cyl 3 - 94 dry 102 wet

cyl 5 - 105 dry 112 wet

plug on 3 was black- dry on the electrode wet on the threads
plug on 5 looked good

all the other cylinders were in the 120-125 range dry 130-135 wet. i know, not the best numbers and yes the rings are tired too. but trying to limp her along throught the winter. runs like crap right now- sputters through out rpm range and stumbles off idle.
 
The proximity of the two low cylenders together and their lower readings would lead me to believe that it has the beginnings of a blown gasket between the two. The symptoms you've described running up the rpms and stumbling off idle could be the result of a blown head gasket but your usually down in the 30psi range and have residue in the coolant/oil when that happens. I've had less run better, so check for intake leaks and ignition related items before you get too deep into the heads.
 
If you use an emissions tester (4-5 gas anylizer) and check your cooling system for HC. That will tell you for sure weather you have a head/gasket problem. Otherwise use a leakdown tester and listen to the companion cyl. for air leaks. Just a few more ideas to throw at ya. LOL.
 
I agree with BORREGOK5, I'd do some more digging before I threw in the towel and pulled the heads. Test, the psi on one cylider dry, then wet the one next to it to see if the readings change in the dry one. Might work? or maybe a test with a air compressor to one cylinder while watching the other? Even pulling the rockers to keep the valves closed is easier than pulling the heads.
 
Smell your exhaust. Does it smell sweet? Is there alot of "steam" coming out of the exhaust after warm up on a warm day? I had a blown gasket and I noticed the above symptoms. On mine, the anti-freeze never made it to the oil because it was being burned.
 
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