jolly77

hi all

Been offered a 300zx non turbo with an engine problem.

engine starts first time but when the engine has warmed up it begins to pressurise the water system and blow water out the header tank. Been told its possibly a head gasket problem which isn't to bad as the car is cheap. Do the heads crack often on these engines because if its the heads it could be costly. Or could it be anything else ?

thx in advance

warren

Zen31ZR

Blown headgasket would pressurize the coolant sytem right off the bat. You can remove the filler cap and feel the pressure pulses from the engine running, sometimes. Your system may have too much regular water in it, which boils at a much lower temperature than coolant. I'm also gonna say that your thermostat may be bad, or missing altogether. If you suspect a blown headgasket, do a compression test. We can sit here and discuss all day what it may or may not be, so your first course of action should be to eliminate possibilities. Check the engine oil for coolant, it'll look like milk chocolate and be thicker and a bit sticky. Do a compression test. Have a coolant system pressure check done, any shop that changes oil should be able to perform this. Pull the thermostat housing, make sure it's even in there, and that it's not upside down. Do these things and let us know what you find out.

P.S. It's also possible your radiator is plugged, or one of the hoses going to it is kinked.

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1992 Yamaha FZR 1000. 145 Hp, all stock..

jolly77

thx for the info, will check it out and come back to you all

thx

jolly77

one last thing as a theory

if the heads have a hairline crack wouldn't it only show up when the heads got hot and expand? is it best to do the compresion test when the engines hot ?

Zen31ZR

Maybe, but the spark plugs should not be removed from the aluminum heads when the engine is warm, as it can strip the threads. So you're kinda stuck doing it cold. I kinda tend to think its NOT a headgasket, as there would be other signs. Does it smoke white out the tailpipe, warm or cold? Coolant loss would be another, aside from what boils out of the engine when it warms up. The oil thing, as well.

Wouldn't be the first time something unusual has happened, but I think you should start with the simple, easy to diagnose stuff first.....

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1992 Yamaha FZR 1000. 145 Hp, all stock..