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Need some advice on possible 350 blown head gasket and compression questions

This is a discussion on Need some advice on possible 350 blown head gasket and compression questions within the Technical / Maintenance forums, part of the General Discussion category; I'm new here and looking for some advice. The truck is a '90 Chevy full size, engine is a 350 ...

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    Need some advice on possible 350 blown head gasket and compression questions


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    I'm new here and looking for some advice. The truck is a '90 Chevy full size, engine is a 350 with around 200K on it, here are the symptoms: Burning antifreeze out the exhaust pipe, it's making a white smoke/steam that smells like antifreeze. The upper radiator hose has a ton of pressure if you try to squeeze it right after starting the truck up cold and before the thermostat is even close to opening, I'm I'm guessing the exhaust is pressurizing this system? No water that I can see in the oil on the dipstick. Pulled all 8 plugs and did a compression test, the 4 on the drivers side were dry, compression on these 4 starting at the cylinder closest to the firewall and working out was 155, 150, 160, 130. On the passenger side, the plugs from the middle two cylinders had antifreeze on them. Compression on these 4 starting closest to the firewall and working out: 140, 160, 140, 145. While running the compression test (turning the engine over 4-5 times each cylinder) there was actually antifreeze blowing out the middle two cylinders on the pass. side. What I don't understand is I thought a blown head gasket will show low pressure in two adjacent cylinders. The cylinder on the passenger side that read 160 psi had the most antifreeze on the plug and blew the most out during the test. Am I wrong thinking the pressure should be low? Could this possibly be a intake manifold gasket leak? How about the compression, the 130 doesn't look that great, does this engine need rebuilt? I'm just looking for some advice on what I need to do/check next on it. Thanks.
    Last edited by 40cal; 05-30-2011 at 09:49 PM.

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    Re: Need some advice on possible 350 blown head gasket and compression questions

    well a blown head gasket will can cause 2 adjacent cyl. to be low on compression if its blown in the narrow part of the gasket between those two cyl. your head gasket could be blown thru to the coolant ports wich would explain your antifreeze issue and your high pressure in the rad hose too. and correct me if im wrong but 130 for compression is a little low...
    <------Thanks to Mean Green
    1994 K1500 ECSB Z71 5.7L 350
    1997 K1500 ECSB Z71 5.7L 350 Vortec

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    Re: Need some advice on possible 350 blown head gasket and compression questions

    Yeah from what I've heard the 130 is a little low, somebody told me that the difference shouldn't be more than 10% between the readings. I use the truck for hauling firewood and hunting, doesn't have to run perfect but I need it to run. Is there another test I can do to make sure it's the head gasket since the compression test didn't get me any results?

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    Re: Need some advice on possible 350 blown head gasket and compression questions

    You could have a cracked cylinder head? My dads 350 back in the day had the same issue, just another idea for you to check

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    Re: Need some advice on possible 350 blown head gasket and compression questions

    Yup, cracked heads are common in those. Doesn't show up too much in a compression test but that's not much consolation.

    A tear-down and inspection would be in order.

    A blown head gasket between the cyls won't exchange coolant and combustion. No water there. It would have to be blown someplace else. Given how severe it has to be, if it was a gasket, you'd be basically unable to drive the truck.

    I'd bet on a cracked head if I was the betting kind.

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    Re: Need some advice on possible 350 blown head gasket and compression questions

    Thanks guys for the suggestions, for the cracked head, if I pull it would the crack be visible or would I need to get it checked out? Now I just got to figure out if I want to do the work or take it somewhere. I have some mechanical ability, (changed the transmission twice on this truck, replaced a few intake manifold gaskets on 4.3 engines, changed transmission twice in a 3.1 fwd car), time is my main enemy now, I never got to tearing one down this far. What would've caused the head to crack? Does this happen because of overheating or is it just something that happens?

 

 

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