o.k. guys, I am brand new to this forum, and a brand new 1st time corvette owner. I scored a 1989 Chevy corvette white, with red interior, full digital gauges, and removable glass roof. it also has an aftermarket stereo and sound system. only has 54K miles on it and i paid 3500 for it. why i got it so cheap is previous owner overheated engine and mechanic told him the head is warped after he replaced the water pump. i don't necessarily agree that the head is warped because the engine still purrs like a kitten, and no white smoke, and no leaking antifreeze anywhere. i checked the oil and no chocolate milk either. it still will overheat in about 10 minutes meaning temp will climb to 250 to 260 and i will shut engine off. I know the fan works because I turned the A/C on and fan kicks on. what else should I replace? i am thinking replace the thermostat for starters. any direction is greatly appreciated.

 

Definitely do the thermostat. That is usually the only thing needing replacement. A really easy check is to boil it. You can put a thermometer in the pot and see what temp it opens. If it isn't fully open by boiling you know it is bad. Most of these thermostats are open by 185-195.

 

Does it make heat out the heater when you turn the heat on?

Does the radiator get HOT when the engine temp rises over ~190?

 

I'm with topfuel on the t-stat but it seems hard to believe a mechanic wouldn't have at least checked that. Also check the temp sensor to verify it's actually overheating. At 250 - 260 you would probably hear coolant boiling in the motor. If it's not pushing coolant out and the rad is full, why would it overheat?

 

Make sure he put the correct water pump on. They may have installed the incorrect rotation.

 

As all have said Thermostat, good properly mixed coolant make sure it's moving coolant and try to get it clear of air pockets. look at front of Radiator, kneel down by front licence plate and look up under bumper you would be amazed what gets Hoovered off of the road up there also on right side of Radiator schroude were the AC lines come out you can see in between the a.c. and radiator that to can get clogged pretty good

 

Also make sure the thermostat wasn't installed upside down.

 

Are both radiator hoses hot? If so, your thermostat is open. Before I did anything, I would use a combustion leak detector such as https://www.harborfreight.com/combus...tor-64814.html
I would also do a coolant system pressure check. You can probably borrow one of these testers from an auto parts store. If those both pass, then I would wonder how efficient the radiator was. It could be clogged.

 

I changed my fan witch and thermostat to lower temperature.

 

If he's getting to 260, fan on temp ain't the problem. Fans turned on 30 degrees ago.

What needs to happen next in this thread, is that the OP needs to answer some of the questions that have been asked. Otherwise, we're all just WAG'ing at this point.

 

fan works. i changed the thermostat las night and it still gets up to 243 and then fans bring it back down to 220 and then right back up again.

 

Fans are normally on at 230ish and off around 210. Could be a bad sensor. As Tom said you need to check the "actual" temps with a laser type temp sensor. See what the temp is at the t-stat housing and the top and bottom of the radiator. That will tell you if you have an actual temperature problem or just a gauge reading problem.

 

fan is kicking on around 240 and cooling down to 220 and then goes back up. radiator hoses are warm. i did notice it bubbling in the overflow tank and bubble out for a bit

 

i actually put the 180 thermostat in. the fan is kicking on when it is supposed to.

 

Fans should turn on around 230.


Check the actual engine temp w/a temp gun, and verify correct operation of the temp sensor/sending unit.

 

Something is screwy with your fan activation temps. Fan should come on when ecm is at 108c which is 226. knock it down to 100c or 212f. Many things are possible. for what it is worth, i have not seen any significant difference between my dash digital temps and the stated temps that the fan switch comes on.
Couple questions:
- does the car have the boost fan? in front of the rad you can see it if you look up from the front of the far
- what color is the coolant?
- have you ever observed the coolant level in the overflow being "sucked back in" after the car is shut off and cools?

I see no reason to do anything other than rent or buy a cheap cooling system pressure tester. I got one off amazon for like 30 bucks and it does pretty much any type of cooling system.

Furthermore, it is entirely possible that you have a perforation in your cooling system that is *not* the head gasket. In L98's you can leak pressure / vacuum out of the intake manifold base gasket (common) and many other places. Doesn't have to be the head gasket.

Bubbling in the overflow is a significant clue. However that in an of itself doesn't point to only head gasket. You can either have a system filled with air due to a vacuum leak somewhere not allowing the fluid to be sucked back into the rad upon cool down (vacuum instead draws air into cooling system, while fluid stays in overflow, commonly found when hose to overflow tank has small cracks!). This results in perpetual air pockets in the cooling system. which then boils out, and system cooling capacity is reduced. when the system pressurizes again the air pockets will be forced out past the rad cap. its a negative downward spiral. gets worse with every heat cycle. or, like the mechanic likely deduced, you can have pressure leaking into the cooling plumbing via a perforated head gasket or crack in the cooling jacket wall, overcoming the 16psi cap that you have installed on your rad, and then escaping out the overflow. You need to figure out which one of those two reasons you have bubbling in the overflow.

I have had it 3 times on old c4 L98's. Once it was head gasket and twice it was simply cooling system allowing air back in and leaving fluid in the overflow. Once it was the overflow hose itself, and once it was the rearward intake manifold bolts were loose on bank 2.

Being a guy who has bought many c4 roaches i have dealt extensively with the L98 cooling systems. So far I would say we do not have a confirmation of head gasket issues.

Though if it was a mechanic who was uninterested in working on the car, if i saw bubbles in the overflow, i could quite easily see how that could be accepted as a diagnosis.

I am not saying he/she wasn't correct, but you can go through the motions and get a precise diagnosis.

Get a coolant system pressure tester. If you pressureize the system and cannot find any leaking/obvious areas where pressure is leaking, then install a cylinder pressurization hose (it looks like a compression tester, but the hose comes apart with an air fitting. you turn your air compressor down to about 35psi and you jam each cylinder full of air. be careful. the air will push that cylinder to bottom dead center. rotating the engine. watch your hands and chords. If you leave it and get bubbles out the overflow.....now you know you have a perforated head gasket, or cracked block. i've never seen the latter in an l98. pressurize from the back forward. Those two things (cooling jacket and cyl pressure) will tell you the story. I believe there was a suggestion of an exhaust gas detection system in the coolant upthread. this may cut through the bs and get straight to the diagnosis! I have never used one....but if you can know for sure you have exhaust gas in your coolant, you have your answer!

nice find on the car. even if it needs a head gasket job, that can be done for under $200 at home with basic tools! If you are handy, and yes, that includes decking the heads diy! or pay someone to do it if you have the cash.

 

You need to remove the radiator and clean the fins real well. You can't see how dirty till it's out.
Chances are it looks just like this

 

This is a prime example of how much debris these cars can suck up over time.

 

Have the cooling fluid checked for hydrocarbons. If the head gasket is blowing into the cooling system hydrocarbons will be present.