Newbie question on 1982 radiator and temperature

[Harris B.]

Hello everyone, new to NCRS, my second post. Purchased a 1982 about a month ago with 20,000 miles. Car sat in temperature controlled storage for an estimated 20 years. Love it but it has a few issues that I need to sort out.

After engine gets up to operating temperature I find that it maintains about 195 degrees (at least according to the gauge) but after a few minutes the water temperature gauge needle moves rapidly to the middle of the red range and then some 10 to 15 seconds later the temperature drops back down to 195, and then about two minutes later the same rapid movement to the red and then back to 195. This cycle keeps repeating. Obviously very bad for engine and I want to solve this problem first.

I assumed this problem was caused by a bad thermostat. I replaced the thermostat with a new 195 degree AC Delco thermostat (the old thermostat had the 195 stamped on it so I assume it was original - it did not appear to be damaged in any way but I did not test it under procedure outlined in service manual). Sadly, I still have the same issue.

However, after replacing the thermostat, as I was driving, I turned the heater on (temp lever all the way to the right - hot) and fan speed at the third of 4 positions and the issue went away. That is, the needle movement to the red range stopped and the gauge needle stayed at 195. This, of course, suggests to me that my radiator is partially clogged (perhaps not surprising after such long storage). Before I go through the trouble of removing the radiator and having it repaired (tanked, "rodded out", re-soldered, repainted), has anyone experienced this phenomenon and, if so, was the problem due to a clogged radiator?

I plan to remove radiator cap when engine cold, crank it up, and then observe coolant circulation when engine rises to operating temperature as a test to make sure the water pump is working. I also did not notice any white scaling inside the radiator with the cap off (which I thought I would observe on a partially clogged radiator) and the radiator fluid (green, not orange) looks very fresh. Any other suggestions to confirm the issue is, indeed, a clogged radiator, before I remove the radiator. Incidentally, other than the steps outlined in the Chevrolet service manual for removal of the radiator, any tips or suggestions to make the radiator removal as smooth and easy as possible?

Thanks everyone!

[Terry M.]

Re: Newbie question on 1982 radiator and temperature

Hello everyone, new to NCRS, my second post. Purchased a 1982 about a month ago with 20,000 miles. Car sat in temperature controlled storage for an estimated 20 years. Love it but it has a few issues that I need to sort out.

After engine gets up to operating temperature I find that it maintains about 195 degrees (at least according to the gauge) but after a few minutes the water temperature gauge needle moves rapidly to the middle of the red range and then some 10 to 15 seconds later the temperature drops back down to 195, and then about two minutes later the same rapid movement to the red and then back to 195. This cycle keeps repeating. Obviously very bad for engine and I want to solve this problem first.

I assumed this problem was caused by a bad thermostat. I replaced the thermostat with a new 195 degree AC Delco thermostat (the old thermostat had the 195 stamped on it so I assume it was original - it did not appear to be damaged in any way but I did not test it under procedure outlined in service manual). Sadly, I still have the same issue.

However, after replacing the thermostat, as I was driving, I turned the heater on (temp lever all the way to the right - hot) and fan speed at the third of 4 positions and the issue went away. That is, the needle movement to the red range stopped and the gauge needle stayed at 195. This, of course, suggests to me that my radiator is partially clogged (perhaps not surprising after such long storage). Before I go through the trouble of removing the radiator and having it repaired (tanked, "rodded out", re-soldered, repainted), has anyone experienced this phenomenon and, if so, was the problem due to a clogged radiator?

I plan to remove radiator cap when engine cold, crank it up, and then observe coolant circulation when engine rises to operating temperature as a test to make sure the water pump is working. I also did not notice any white scaling inside the radiator with the cap off (which I thought I would observe on a partially clogged radiator) and the radiator fluid (green, not orange) looks very fresh. Any other suggestions to confirm the issue is, indeed, a clogged radiator, before I remove the radiator. Incidentally, other than the steps outlined in the Chevrolet service manual for removal of the radiator, any tips or suggestions to make the radiator removal as smooth and easy as possible?

Thanks everyone!

When you replaced the thermostat did you flush the cooling system and replace the coolant?

[Harris B.]

Re: Newbie question on 1982 radiator and temperature

Terry, thanks for your reply. No, I'm afraid I did not flush the cooling system and I did not replace the coolant. I guess I need to try that before I tackle removing the radiator. I will do so.

[Terry M.]

Re: Newbie question on 1982 radiator and temperature

Terry, thanks for your reply. No, I'm afraid I did not flush the cooling system and I did not replace the coolant. I guess I need to try that before I tackle removing the radiator. I will do so.

I use a cooling system cleaner called RMI-25 in my drivers, but they have all aluminum and plastic in the cooling system -- of course there is the iron engine also. This product requires some driving, heating and cooling cycles, to be most effective. There are other products that may work as well, or nearly as well, and be more suited to a copper, brass and iron system.

I am not familiar with 1982s. Does your Corvette have an electric fan, or is it engine driven like the earlier C3s?

[Harris B.]

Re: Newbie question on 1982 radiator and temperature

Thanks, Terry. It actually has both, a fan driven by the engine and then an electric fan attached to the front of the radiator than is activated when the engine gets to a certain temperature. The use of the cooling system cleaner sounds good and I understand the need to have several heating and cooling cycles, to perhaps to break up some of any clog.

Harris

[Patrick H.]

Re: Newbie question on 1982 radiator and temperature

Don't forget the two drains on the block, one on each side, just above the oil pan rail.
They might be stubborn, and I've replaced more than one set with brass plugs rather than the original steel.

Did the condition then return after turning off the heater?
I wondered too about air in the system or similar which could cause fluctuations.

[Terry M.]

Re: Newbie question on 1982 radiator and temperature

Patricks post brings to mind an incident we worked with not too long ago. The member had a small leak in the cooling system. It was small enough not to be bothersome (he didn't mention it to us) but it prevented the cooling system to come to full pressure. The system boiled over as a result. We were troubleshooting the boil over without realizing about the system leak.

Be sure your radiator cap holds the pressure required. In your car I am sure there is an over-flow tank so the system, if unpressurized or if not holding full pressure, would flow into the over-flow tank and not on the ground. When cooling down the coolant would be sucked from the over-flow tank like it is supposed to. Take a look at the radiator cap. There is a tool to test them, but most folks will just get a new one. Be sure the radiator surface the cap seats on is clean and not mall-formed.

[Patrick H.]

Re: Newbie question on 1982 radiator and temperature

The radiator cap came to mind for me as well.
I think you can buy brand new GM radiator caps for an 82 which, while cosmetically different, would function fine. Auction sites tend to have better prices than dealers on these.

[Terry M.]

Re: Newbie question on 1982 radiator and temperature

The radiator cap came to mind for me as well.
I think you can buy brand new GM radiator caps for an 82 which, while cosmetically different, would function fine. Auction sites tend to have better prices than dealers on these.

For the purposes of this kind of test any new radiator cap that is specified for a 1982 Corvette from your FLAPS (Friendly Local Auto Part Store) will work fine. I would expect a generic radiator cap to be much less expensive than a GM part, but I have recently been surprised at how competitive GM parts counters are getting lately.

[Richard G.]

Re: Newbie question on 1982 radiator and temperature

In my opinion it is unlikely that the water temperature could change in value in that short of a time. Especially with an operating thermostat.
You should attempt to isolate the issue between electrical (gauge) issues and mechanical issues like plugged radiator before pulling the radiator. As pulling the radiator in these cars is no fun. However I agree flushing the system is a really good idea.

Use a infrared thermometer to confirm the radiator and hose temperatures. These infrared thermometers are inexpensive these days typical about $35 dollars. Remember they are more accurate on black parts and can read instant changes in temperatures. An alternative is to purchase a manual gauge and install it for trouble shooting purposes. If you just idle the car, without moving, it can be installed temporally without modifications to the vehicle.

I do think it's interesting that running the heater made the gauge readings steady out. I agree some type is plugging is possible/likely.

You mentioned this is while driving the car. What does it do while idling? Remember to check the front of the radiator for debris and confirm the fan clutch is working as designed as well as the electric fan switching.

[Harris B.]

Re: Newbie question on 1982 radiator and temperature

Yes, I forgot to mention that at idle the gauge stays at 195, and I let it idle after a long drive (with heater on). The gauge needle does not move from 195 during a long idle. This suggests to me that at idle, with no load on the engine, the radiator, thermostat, etc. can manage the heat. I will perform the tests as everyone suggests and see what happens.

[Patrick H.]

Re: Newbie question on 1982 radiator and temperature

Generally there is more load at idle than when moving because there is far less air flow. So, if stable there that's a good test.

Also check that the temp wire isn't accidentally grounding itself for brief moments and causing fluctuation, which is I think the direction Richard is thinking in the post above.

[Richard G.]

Re: Newbie question on 1982 radiator and temperature

Some more interesting information can be found here:

http://repairs.willcoxcorvette.com/wp-content/uploads/2010/08/1956-1982-corvette-temperature-gauge-help-guide.pdf

[Harris B.]

Re: Newbie question on 1982 radiator and temperature

Richard, although I have reviewed many of the Willcox articles, I have not seen the one on which you provided the link. This one is very helpful. Thanks for providing that link.

See, I agree that I should be checking the electronics of the gauge because the unusual event I describe of a rapid rise of the temperature needle (pointer) followed 10 to 15 seconds later with an equally rapid downward movement of the pointer. Nevertheless, this phenomenon stops when I turn on the heater (suggesting that the heater core is serving as an expanded radiator to overcome any clogs in the main radiator and thus, not an electronics issue).

I am still going to exhaust all of the tests that our NCRS colleagues suggested first. I really don't want to take out my radiator as that looks like a chore.

[Dick W.]

Re: Newbie question on 1982 radiator and temperature

I use a cooling system cleaner called RMI-25 in my drivers, but they have all aluminum and plastic in the cooling system -- of course there is the iron engine also. This product requires some driving, heating and cooling cycles, to be most effective. There are other products that may work as well, or nearly as well, and be more suited to a copper, brass and iron system.

I am not familiar with 1982s. Does your Corvette have an electric fan, or is it engine driven like the earlier C3s?

Not to rain on the parade but be prepared to have a leaking radiator once you run the cleaner through it. From prior experience of owning a radiator repair shop, a 36 y/o radiator is most likely to leak, how much is anyones guess.