I'm going to describe my problem and appreciate any help. Last year the car started to overheat (guage spiking 2 250) at standstill. When it got moving it came down to normal (210). I replaced the thermostat (160F) in the fall before putting it away and it seemed to help the problem a little but not good enough. I have records back to the 80's for this car and as far as I can tell, the radiator has never been touched (77k mi). I've checked the obvious stuff like the right side of the rad being hotter than the right and the upper hose being pressurized while running. I know the water pump was replaced at probably 60K. Before I pull the rad and have it re-cored, is there anything else to check? 2 mechanic buddies told me to re-core but I like to hear all opinions. Also, any tricks to pulling that rad? It looks pretty straight forward. Thanks in advance.

 

If it just heats up at idle and then cools off while driving, suspect the fan clutch.

 

Jud is right.... if it is cooling while going down the road it is not a radiator problem.... i bet there is something with the fan/clutch assembly.

Sully

 

Your radiator is probably 'limed-up' on the inside of the cooling fins. Your best solution would be to remove the radiator and take it to a good radiator shop [that does work on vintage car radiators]. They can tell you if there is any significant damage and whether your radiator is a good candidate to clean, repair, re-core or if you should just replace it. If the fins and solder joints aren't damaged, they might be able to clean it out well and just touch-up any solder areas that require it (estimate $100). If it can be saved and re-cored, that will cost about $300. A replacement radiator will cost $450-800, depending on how 'original' you want it to be.

The "budget" method is to buy some radiator CLEANER (not radiator FLUSH) from your auto parts store and follow the directions exactly as written (any short-cuts will significantly reduce the benefits of the cleaning process). If your radiator hoses haven't been replaced in the past few years, do them too. 50%-50% mix of anti-freeze and distilled water and a new 180F (or 160F, if you don't mind slow warm ups) thermostat and you should be good-to-go.

 

P.S. To check your thromstatic fan out....get your car to normal operating temps, stop your car and pop the hood; then as you are watching the fan rotate, shut off the car. If the fan takes more than a couple of rotations to come to a stop [after the motor has stopped turning], the fan clutch needs to be replaced.

 

you said that at highway speeds the temps are fine but at low speed or idle they go up.
most low speed cooling issues are caused by one of two things: airflow management and/or ignition timing.
Hi-speed cooling issues are caused by radiator problems or restricted air or coolant flow.

since we are dealing with a low-speed cooling issue we only need to look at airflow management and timing .

1. airflow: you have all the proper radiator and core support seals in place, correct? If so we can move on. if not, get them on before anything else.
are you running the factory stock fanblade (please don't tell me you have a flex-fan on there) and fan clutch?
As already mentioned, check the operation of your fanclutch. Get the motor up to operating temps than turn it off. the fan should stop within 1 to 3 revolutions. If it takes much longer than that or just freespins it's time for a replacement.
Do you have the fan shroud in place? the fan shroud is very important to the cooling system and you will lose major efficiency without it.

Timing: You didn't mention if your timing had been changed at all before your cooling issues started but timing can play a very big part of how cool or hot your motor runs.
what EXACTLY is your timing set at? what is initial timing and what is total timing and when doesn't the total timing come in by?
Are you running a vacuum advance cannister? If so (you should be!) what are you timing numbers at initial and total timing also with the vacuum advance connected?
Is your vacuum advance connected to full manifold vacuum as opposed to ported or timing vacuum?

You also mentioned you had a 160º t-stat in the car and you replaced it. The t-stat will not control what temp your motor runs at, only the MINIMUM operating temp. On your car the stock unit was a 195º t-stat. If you still have all the emission equipment installed on your car you should have a 195º t-stat unit in there. If the emission equipment has been removed off your motor you should put in a 180º t-stat.
I recommend buying either a Robert Shaw or Mr. Gasket (same as a RS unit just marketed under the Mr. Gasket name) t-stat unit as these t-stats are designed that if they fail they fail in an "open" position and still allow coolant flow. Regardless, unless your old t-stat was bad and completely failed to open it's not the cause of your problem and we know the old one didn't fail or otherwise even your highway speed temps would be high also.

 

If its an airflow issue you could have some debris blocking the front of the radiator. If you don't have air, this will be easy to see, but if you have air, the condenser will be blocking your view. To clean, spray water from a hose from the engine side to flush any debris out.

 

Your t-stat was a 180F unit from the factory...195F was not standard until later. Poor heat transfer (such as with a crudded-up radiator) will cause reduction of cooling capacity, whether at high or low speeds. It would affect low speed cooling worse because of the reduced airflow. Take advice as you see fit. A radiator that hasn't seen good maintenance in 30 years is a "no brainer" for needing a good cleaning, IMO.

 

Jud, Sully, 7T1---I checked the fan clutch. It spins way more than a few times when engine turned off so I'm going to replace that first. Thanks. Paul--I checked for debris...a little at the bottom that I cleaned out. Barry---The last time I did the timing (a few yrs ago, I set it at stock spec. Everything under that hood is bone stock. Thanks for all that advice, I'm going to go over all that too. I think that the culprit is the fan clutch right now...

 

You are welcome and hope you get the problem solved quickly.

 

Barry has the answer! Follow his instructions. If you still have overheating problems - very doubtful - then look at the radiator. My original stock aluminum radiator has 136K miles on it and my car does not overheat, even idling around in 100° weather.

Cheers,
Pete

 

I myself am facing this overheating demon now for the past two days. I have only replaced the tstat housing gasket. I had finally finished all the other stuff that was not working or broken like a rebuild of the guage center, vavle covers, gas tank float, passenger pwr window asmbly, pwr drvrs seat, wiring in the center consol, top seals, lights switch, polished rims, etc. Everything was beautiful. It was to the point on the last run that it put a smile on my face just driving her around town. I even had her running awesome in bumper to bumper traffic at about 90f. She still didn't give me a problem. I'm all excited and stay up finishing her for a saturday afternoon meet of other corvette owners. I finish and go to bed. The next morning while waiting on the misses to come down I decided to get the ac running for her. Then terror as the temp guage went all the way to 260. I immediately shut down and we took the good ole CRV. I thought all day about what I might have messed up. Not a thing. In my trouble shooting of this issue i have verified all that ive read in these posts. The last test which was just simply removal of the tstat seemed the most promising as the temp would shoot up before now took more time but still managed to climb to 220 before I shut her down and started typing this. Help if you can. 82 sb with crossfire removal conversion.