i have an 88 irocz with the 350 tpi and i just replaced the water pump and the thermostat. I have my fans bypassed and it keeps overheating i did a compression test on one side and the 2 outside cylinders are at 120psi and the 2 inside are only 100psi. so i'm just wondering if maybe my head gasket is blown or i don't know so if anyone has any suggestions I would really appreciate it

thanx splinterL98

 

splint diagnosing is tough over the net,but your compression variance aint that bad,some folk use 10-15 differnce as a rule of thumb and u aint that far off.id suspect if you had a blown gasket your compression would be lower and there would be other signs also,,ie white smoke,coolant loss,milky oil on dipstick..any ways one of the most common causes and easiest fixes for overheating on most cars is the radiator cooling fins...have you cleaned them out lately or blown them out???youd be suprised att how much road grim gets caught up in there and blocks the fins over the years...block fins =no air moving over them=over heating...rememebr if u ever look at a z,the opening for the radiator air is tiny,so you need all u can get.heck gm even had to put that silly deflector on the underside to help force more air into the radiator...thats why youll also over heat w/o the deflector...you do have that deflector right????

 

Yep, the deflector is definitely a big part of keeping these cars cool. You might just double-check to be sure that a previous owner hasn't "scraped it off" on a curb, or even partially broken it so that it's not able to function correctly...

I'd tend to agree with Anthony, if you had a blown head gasket, you'd be seeing other symptoms as well - I've been down that road...

The only other thing that comes to mind right now is to check that airflow isn't somehow allowed to go around your radiator instead of through it - when I removed my A/C (it didn't work, & I didn't need it where I was living then), it created a fairly sizable gap at the top of where the radiator met the cross-brace. When I had to deal with hot weather later, BOOM, instant overheating issue...

Good luck, let us know if you think of other info you can give us, that might help get you a better "guess"...

 

Couple other things can cause overheating. Ignition timeing being too retarded insted of advanced and when you did the water pump and thermostat did you get all the air out of the cooling system? Let the car run with the radiator cap off till the thermostat opens up then top off the coolent and replace cap.

 

i'mn just speculating but if someone changed the heads and didnt torque them properly or out of sequence, or say the head was removed from the block and un-torqed out of sequence, wouldnt this result in slight warpage of the head and account for the change in psi?

also someone said 10-15 is ok, i'm assuming they meant 10-15 percent in which case 120 psi is 20 percent more than 100 and 100 psi is 16.5 percent lower than 120, either way this is beyond the said threshold

 

Did you get the right kind of waterpump on there. I have heard the L98's have opposite/reverse flow waterpumps when compared to normal sbc waterpumps (non LT-1). Definatly check out the airdam and make sure it's there too. You might need to get your radiator rebuilt too. I pulled my radiator off of my Iroc and took it to a radiator shop and they took it apart and cleaned it out real good for like $60. Take one of those laser guns that read heat and check different points in the radiator while the car is running. If certain spots on the radiator has a big gap in temp compared to other spots, your radiator could be clogged up.

 

my car has half the power it used to have and i can smell antifreeze burning my thermostat housing i think is leaking would that make it so that i am losing power. it doesn't seem to be overheating anymore i replaced the battery but even before i replaced the battery the car still had half the power.


SplinterL98

 

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Originally Posted by irco crazy

hey, have you tryed the fail safe thermo. that is probley the best thing to start with. Inspct the radiator, is it leaking?
this is what happened to mine. right around the upper part of the right tank. the new water pump may be bad.I also recomend looking at the condenser, is it cloed up?

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i also just recently took out my radiator (its too cold in wyoming to overheat wihtout really trying to) and when i took out the condensor there was about 5lbs of leaves stuck between the condensor and radiator. the reason why some 3rd gens tend to overheats is b/c the stock cooling fan switch doesn't turn on till your temp reaches 238* and shuts of at something like 218*, this was for emmisions/gas mileage. but since you've wired them full time that can't be it. if your fan shroud is somehow on backwards that could cause and overheating problem as well as a broken or missing air dam like everyone else has said. as long as the waterpump is flowing and not leaking out the weephole i wouldn't think it'd be my first thing to look at. you said that you replaced the thermostat but did you replace the radiator cap? if the cap isn't holding pressure then your coolant will boil at a lower tempurature than if pressurized. if you get desperate you can try using a lower temp thermo but i wouldn't recommend it unless you can't find the problem elsewhere. also, just out of curiosity, what mixture antifreeze/water are you using. while antifreeze increases and lowers the boiling and freezing points of water it is less effective at transfering heat like water is. antifreeze also has some (can't think of the word) protective properties that help to prevent junk forming in the system. if you do have junk in your system or even an air pocket a coolant flush will get rid of that no prob. also i don't know much about it but can that "water-wetter" stuff be used in street cars like ours? i know i just rambled a bunch of stuff off but i'm trying to think of any possible reason off the back of my head. hope i could help you

 

yes water wetter can be used in street cars.

sometimes the heater cores can get stuffed up too. can get a flush kit and splice it into your heater core lines and do a flush and see what happens after that.