I found an awesome thread the other day on how to check compression. Well of course I can not find it again!! I am now ready to check the compression and not sure exactly how!!!

 

Well since it would probably take me longer to find the thread than to retype it, here goes...

You first want to remove the spark plugs (all of them). You may have to disconnect the steering shaft to get to the #3 cylinder to perform the compression check (and possibly to remove the spark plug if you are unlucky). For that, check the DIY section for help on the #3 spark plug.

For the compression check, simply screw in the fitting from the compression tester and affix the gauge. Then turn the engine over with the starter for 2-3 seconds. Write down the cylinder pressure and move on to the next one. Once you get all of them, if one cylinder is quite a bit lower than the others, squirt some clean engine oil into the spark plug hole and repeat the test. If the problem is excessive blow by past the rings, the oil will seal the gap temporarily, restoring cylinder pressure.

You can pick up a compression tester from your local autoparts store for around $30USD.

 

when you check the compression i was always told if the cylinders are within 10% of each other it is fine. if its more then 10 % then you got a problem somewhere (rings,cracked head,head gasket.....) is there a reason why youre checking compression ?

 

Thanks for getting back with me. Well we have now undoubtly determined it is the heads. So any suggestions on how much to sell it for?? 2000 Blazer 2wd 169000 miles new water pump, rear brake calipers, radiator, thermostat, oil cooler lines. I have no idea what to sell it for with blown heads.

 

well not sure how mechanically adept you are.. but is it heads or head gasket????? the gasket kit I believe is under $100 and if you do the labor yourself... I wouldn't see that as something to sell a car over.. myself.. once I have to pull an engine I'll think of selling it.. (only cuz I dont have the garage or engine picker/stand<<< due to not having a garage...)... but all of that work can be done with the engine in the vehicle... tho I would reccomend as with most.. if you have the heads out you migh as well send them out to have them checked cleaned valve job and such... total MAYBE$500-$750 and you're truck will be running like new.... and you'll actually get some good use out of that new radiator and waterpump...lol

 

when you do a compression test and notice the 2 cylinders that have the drop thats wehre the blown head gasket will be. is your oil milkey? are you burning white smoke ? do you notice a loss in power ? these are a tell tell signs of a blown head gasket. if its a cracked head depending on where the crack is you might not notice milkey oil or burn white smoke but you will notice a loss in power. you mentioned a new radiator and water pump did you ever overheat the engine ? if so thats prolly the cause of the head/head gasket problem. if you want to keep the truck and want to put the money into it if it needs it you may as well rebuild the engine (139,000 sounds a little too low for a rebuild but you never know) or if you just want to rebuild it while the heads are off. if you want performance now is the time to throw in a bigger cam and maybe have some head work done as well. if thats the case then rebuild the motor.