Brenden Rogers

So this problem started several days ago and I haven't managed to find out what is causing the overheating. I was driving down the road when my water temp shot up to 290. I pulled over and popped the hood. The coolant reservoir was overflowing and boiling. I let the car set and cool and started back to my home. I was going 55mph and the car temp kept increasing. I pulled over again and waited 30mins. I managed to get back home safely with a temp of 170. The next day I went and tried to find out the problem was. The first thing I did was check the radiator. I figured it was blocked since as I drove, the temp still increased. The radiator was clean and unblocked. I then started up the car and let it idle. The cars temp increased fast. Both fans kicked in but they effected nothing. After awhile, I heard a high-pitched whining noise. It was the water pump. I figured that was it, the water pump must be broken or breaking. I replaced the pump along with the thermometer. I let the car idle again and it stayed around 230. I then went for a drive, as I drove, the temp started to decreased. One thing I noticed though was the analog water temp gauge seemed to be broken, it went past 260 and stayed there, also when I stated the car up, both fans started running and didn't turn off. The car seemed to run fine as I drove. Near the end of my drive though, the temp hit 150 and stopped. I pulled in to my drive and the popped the hood. It was boiling again, steam coming from both the reservoir and engine this time. The thermostat stayed at 150 though. It never increased or decreased. I believe the problem may be the radiator but I might be wrong. Any information helps.

My Car:
1994 Corvette C4
New water pump
New thermometer
Used to drive just fine. This never happened before.

A Peter C4

You say rad. was cleaned, did you remove it and clean all the cooling fins for good air flow and flush core for good coolant flow? Did you use LT1 type thermostat to replace old one? LT1 reverse flow thermostat are dif. than standard type. Was system clear of air in coolant=bleed air out?

Brenden Rogers

I believe the radiator may be clogged or have some flow problem. I haven't removed it from the car yet. I plan on giving it a deep clean before the end of this week. I'm pretty sure I have the right thermostat. It was listed in the computer at AutoZone as compatible. Now about the air bleed out, that's something I haven't done yet.

A Peter C4

To clean cooling fins you have to remove the rad. This is a well known problem with C4 cooling issues. It is not that hard to do just the 6 little screws at the bottom, have to remove air pump on driver side then replace nut clips onto the shroud opposite so screws go in from under the front where air comes in to cooling area, IE take nuts off shroud and put on piece that stays in car, you'll see what I mean. to fill the system just fill and start engine with cap off and keep filling until warmed up and full then put cap on while engine is still running, be sure overflow tank has coolant in it so it will self fill when it cools. Let cool run up to operating temp and cool again, 3 times, this should bleed all air out.

Brenden Rogers

I've removed and cleaned it before, it's pretty easy.

A Peter C4

OK good luck

don hall

Symptoms indicate a ruptured head gasket that is allowing exhaust gas into the cooling system.

There is a simple test to confirm exhaust in the coolant:

http://www.superchevy.com/how-to/add...ally-speaking/

Brenden Rogers

Awesome, I'll be sure to do some of the tests when I go though the car this week. Thanks for the reply.

don hall

I hope "awesome" is in reference to my response, and not to the revelation that you may be replacing a head gasket, as it is not an inexpensive procedure.

jmgtp

Head gasket isn't an expensive fix - presuming you are doing the work yourself. Throw in a water pump, radiator, hoses etc. it's more pricey. Get heads decked add more $.

Years ago my 94 overheated. It was a small leak in the radiator that introduced air. LT1s HATE air. My car did all the weird hings you describe. I now have a new aluminum radiator, waterpump, hoses, thermostat etc. I replaced both head gaskets out of caution. I brought the heads to a machine shop to get checked for cracks and warpage. No cracks but a tiny bit of warp that they took care of.

Guess my point is - fix it right now. If it got to 290 you likely blew headgaskets and warped the heads a bit.

Brenden Rogers

Thanks for the reply. I ordered a aluminum double row radiator from Dewitts Radiators that I'm gonna replace the old one with. I'll definitely check the head gaskets when I go to install the radiator.

Aerovette

I had a C4 do exactly what you are describing and I was lucky. It was air in the system. Took a long time to finally reach that conclusion but once I got the air out, never another problem. Hopefully you will be that lucky.

Brenden Rogers

Thanks for the reply. Hopefully I'm that lucky. Knowing my luck though, my entire coolant system is probably messed up.

Brenden Rogers

I just remembered this. When I started up the car with the new water pump, my oil pressure and temp were higher than normal. Could that be a symptom of a gasket problem?

Cliff Harris

The easiest way to check for a blown head gasket is to take all the spark plugs out and then spin the engine with the starter. If the gasket is blown, water will come out of the spark plug hole(s).

don hall

Cliff, if the breach in the gasket is only allowing exhaust gas into the coolant, no coolant will be evident at the plug holes.

Brenden Rogers

Would high oil pressure and higher than normal oil temp be sings of a head gasket problem?

don hall

If the coolant temp is above normal, that would have an effect on the oil temp. If the oil temp is shown as being high at start-up, you may have a defective gage.

Are you reading the temps digitally, or by analog?

Brenden Rogers

I was reading the temps on the digital display. The oil temps started normal and were high after idling. The oil pressure was higher than normal on start up though.

don hall

What was the coolant temp when the oil temp increased?

The oil temp will lag behind the coolant temp at startup.