Just picked up a 91 the other day. Took it out for a drive last night to make sure everything was good.

it was low 50s and chilly out. The car never got up to temperature even after driving for a 45 minutes + with half of that on the highway. Heat wouldn’t warm.

idled for about 5 minutes then temp reached around the 230-240 point but right when I got back on the highway it dropped back down to 120-130. Shortly after SES came on, but I don’t have a OBD 1 reader on hand.

there is a whirring noise that I have yet to trace...but I did smell a slight burning coolant smell.

Doing the t stat today. What are the chances the water pump is bad? I can’t see any visible leaks. Only hear the whirring of a bad bearing somewhere on the front of the engine, can’t tell if it’s the AC compressor or pulley

 

Should just do a pressure check and resolve all the coolant leaks at the same time and be done with it.

Sounds like there isn't even a thermostat installed. If there is, then it's either bad or too low a temp rating.

There's a lot of places it could be leaking.

Got a picture of the motor?

 

Stethoscope to pinpoint the source of the bearing noise. A long screwdriver, dowel rod, length of hose, etc, will work. Obviously, be careful around moving parts.

Live well,

SJW

 

Even without a thermostat it should not get down to 120 while running. I suspect a faulty sensor. Dan

 

I agree, it sounds like a failed or no thermostat situation at all. My car behaved the same when mine failed.

 

If the engine is running that cold you would be getting extra fuel for a "cold start" situation. Is the exhaust rich or blowing black smoke?
That coolant smell could be from under the hood, under the dash or out the tailpipes. I would stick a Coolant test strip into the coolant just to be sure the head gaskets are okay.
Feeling the carpet under the passengers side of the dashboard might tell you if the heater core is leaking.

I have never heard of a V8 running down the road at 120* even without a Thermostat, like mentioned above the sensor and the thermostat might both have to be replaced. The first whirring sound my 1988 C4 had was on the idler pulley which is not hard to replace. I do get some noise from the A.I.R. pump as well as it whines a bit. Focus your hearing in different areas to find the whining part, just don't get caught by a Serpentine Belt.

Since the Corvette is "New to You" I would go through all the major components and verify that they work and are okay for usage on the highways. I flush Coolant, Power Steering, Brake Fluid along with replacing the basic maintenance items like Thermostat, Radiator Cap, Coolant, Brake Fluid, brake pads, serpentine belt, the hoses that connect the radiator and any other hoses that look weak or are soft. I also check the vacuum lines to make sure they are tight and still usable and that everything is connected that has to be connected, i.e. EGR, EGR Vacuum Solenoid and Fuel Pressure Regulator. I would inspect the wires and Distributor cap and replace if needed. I would pull an easy to get to Spark Plug to see the age and condition to decide on replacement.
The Oxygen sensor has a limited life so I generally replace those just to be safe.
The oil would be changed (no matter How Old they tell you it is) along with new Oil Filter, Air Filter and Cabin Air filter. One item I watch before replacing is the Mass Air Flow Sensor. It is a fairly complicated system of cleaning the wires used to measure the air flow, it uses two separate relays and if you ever replace one do the other at the same time, lesson learned painfully/expensively. Also be sure there are no leaks or soft spots on the hose that feed the air into the throttle body, there can be absolutely no air leaking into this hose or the engine will react strangely.

Best of luck getting everything solved easily and in time for the Summer!

 

no thermostat it is. Old one stuck wide open. Put the new one in, idled 10 min and got up to operating temp just fine.

now it’s time to take it for a drive to see if it drops back down.

noise seems to be coming from either WP or AC compressor. Highly suspecting the WP becuase the noise was louder under the intake tube. Got the new pump on hand will replace it anyways when I get a chance.

 

Got to test drive it. Still kinda wacky. But I’ve never owned something this old.

temps stay about 170-180(to around or just under half way point)while cruising ~70°F ambient temp. Park and idle for 5-10 min and needle moves up to around 220°F, radiator fan kicks in and temperature stays there.

Does this sound normal? I know the temps are all within range but I’ve never seen anything like this. Oil temp stays about 140°F. Still dont have heat. Suspecting a heater core issue. Summer car only so I’ll get to it when I get to it. Just want to make sure I don’t blow the engine early in the season.

 

thanks for the advice!

I’ve gone through the car somewhat and everything looks very well kept and a lot of the stuff is new. Brakes, tires, filters. NAPA had a sale on 5w30 today picked up 5 quarts will probably Change later this season. Coolant flush today running pure water with whatever’s left in the system. Will drain and fill again after I do the water pump.

engine has a slight misfire shake at idle when cold. Still have to figure it out. Exhaust smells fine. Did help alittle when i ran seafoam in the tank and now with some fresh 93 octane in there. Still shakes alittle. Probably replace plugs and wires soon.

 

Mostly normal. The fan once it kicks on, should be able to drive the coolant temp down...then shut off -especially in 70* temps. The temp should rise, fan should kick back on and repeat. I'd check for debris between the front of your radiator and the rear of your AC condenser.

WRT "no heat", is the cooling system topped off and no air? If you rev the engine up, does that get you heat from the vents? Low coolant could also cause the fan to keep running.
After that, check the heater core hoses, the coolant bypass valve in those hoses and finally, the blend-air door actuation




Seafoam. Yes, I'd fix the actual problem, and checking wires, plugs etc. is a great place to start.

 

The fan kicks on and doesn’t shut off until I start driving again. Possible faulty coolant temp sensor? Even last night with the stuck T-stat and 50° ambient temps, the fan kicked on at 230 and stayed on until I hit the road. Seems odd, but certainly not out of line for a 30 year old car.

Coolant is topped off right now. Both upper and lower tank full. Bled the system by idling for 15 minutes with the upper cap off. Heat really isn’t that big of a deal since it’s a summer car anyways. But it’s nice to have alittle heat when it gets chilly at night.

 

Not a faulty sensor. Fan is supposed to turn on somewhere around 230....and you say that it is. The problem is that the fan isn't driving the temps down. It should. Driving it provides MORE air flow, so the temp goes down, but if it were my car, I'd look for the cause of that....I'd start by looking between the radiator and AC condenser.

 

It's surprising how much schmutz you can find in there in an otherwise super clean car.

 

I have never had my oil stay at 140 with the car fully warmed up and driving. Dan

 

Did you ever pull the code? If the SES light came on, there should be something there.

 

SES went off itself after I did the T stat. I don’t have an OBD1 reader but I highly suspect it had something to do with it.

 

If the light went on, there should be a historic code (h##). You can pull the codes without a reader, see:

http://www.neilkline.com/Tech%20Tips/obdcodes.htm

 

I had similar issues with mine overheating when I first got it. Turns out the previous owner had installed the wrong water pump. SBC has two water pumps: one with a short snout and one with a long snout. Except it doesn't just have two - it has three. The Corvette has a unique WP that is (I think) a little longer than the short one, and more importantly designed to spin the opposite direction. In my case it was visually apparent that the WP pulley was about 1/4" misaligned.

 

Any time a C4 has had that random misfire. heating up at cruise speeds etc wound up being a head gasket on its way out hope thats not whats going on.

 

I don't think that he said that it was heating up at cruising speed. It was the opposite.