This is what i'm working with. 89 TPI 5.7. This car was supposed to be an upgrade for my little sis. I have rebuilt the entire engine. Line bored, new bearings, rings, etc. etc. The radiator is new all metal (prob brass or bronze), new thermostat, heavy duty duel fans both on full time, verified water pump is flowing, no cat (no emmisions in Florida), flowmaster muffler not clogged. Radiator full, stat working, at idle it stays nice and cool. If I bring the rpms up or even put it in gear for a minute or so it heats up very rapidly till it stalls, and I can hear the water boiling over. Compression read from 148 to 160 across the board. I haven't verified that it is the correct reverse rotation water pump yet thanks the lovely hurricane rain bands. I bought the car from a crappy little buy here pay here with now knowledge of the vehicles mechanical past. Its got ttops slotted rotors kyb shocks, BBK tbody. No rust or dents, for 1500 cash so I thought I was getting a good deal. Now its a headache. Does this sound like a cracked head to anybody?

 

Before you do anything expensive, check thar the thermostat is facing in the right direction. If it is backward the pressure from the waterpump will force it shut. Also check that you have the right waterpump. Pumps for V belts "usually" turn in the opposite direction than those for serpentine belts. Check for collapsing radiator hoses when revving the engine. Make sure the radiator if full and not airbound. If these things check out you will then have to look for more expensive fixes.

 

it does sound like the water pump IMO

 

I know this is an old thread but, man I have the same problem with my '87 Z28. It has a new thermostat (it was overheating before I put a new one in and discovered the guy who owned it before me had taken it out completely), got a new radiator, and the water pump appears to be functioning. I'm not too awfully knowledgable or mechanically inclined (I can fix the basics) but would the coolant heat sensor have anything to do with why it's overheating? It doesn't take very long to overheat on me. I'm about ready to sell this car because it's been such a thorn in my side and I also got mine for dirt cheap only a year ago ($1400). I knew it would be a project, but it's been a snowball from hell.

 

Many times when a car overheats in a very short time, it is the result of a blown head gasket. The problem is that in some cases the gasket is not blown badly enough to show up under a compression test. Make sure youc heck out the entire cooling system, and make sure the fans turn on and run in the right direction, before messing with the heads.

 

I have 2 V8 camaros, an 88 IROC-Z and a 94 Z28.....my 88 runs ok for about an hour, give or take and my 94 goes about 10 miles, but they both run hot. Warm enough to make me uncomfortable driving them. The 88 gets to ~170/180 for about an hour or until gas is used generously....then it goes up to 220, stays there, and climbs to where i have to drift down a hill or shut it off for a while. I cant explain it. The radiator, and water pump are new, and fans are working. The thermostat also works.
The 94, my current driving car, says it runs steadily between 215 and 235.That is VERY warm already. However, my heat is not warm until the guage reads about 225, and there are no warning lights that come on, and no bubbling or boiling coolant in the radiator. The coolant level light is constantly on, although i have a full radiator with a 50-50 water to antifreeze mix. I havent actually heard a fan, though they may come on, but could it be a faulty temp sensor? the thermostat is opening. if it is cool, it runs right on the middle hash mark on the guage. is this normal to run at 210? any feedback is appreciated..


Thanks, Chris

 

Stock thermostat on the 94 is 185 deg.
Normal operation 185-203 deg
Primary fan or low speed ON @ 225, OFF @ 217
Secondary fan or high speed ON @ 232, OFF @ 224
Radiator cap vents @ 257 @ sea level, 15 PSI cap.
PCM will set high temp code @ 284 deg. (DTC 14), kinda late in the game to do much good.

The 94 fans were wired two ways. Early 94s turned up one fan at the time as needed, the late models turned up both fans at one time but cahnged the fan speed from low to high & back as needed.

The engine can probably run safely @ 250 degrees, but make sure you are using anti freeze otherwise it will boil over.

The crossflow radiators that come on these cars can clog one tube at the time. A quick check, with the engine on and at running temp ( stat open), run your hand across the radiator from top to bottom. The radiator should feel equally warm top to bottom. If you feel a cold section, the radiator is partially clogged. Watch out for the fans.