Overheating 79 Spider

[barnesjtsl]

Drove to work this morning. About 32 miles. Cool morning around 50 degrees. My temperature kept fluctuating from around 195 to the redzone. Would just touch the redzone when I traveled through the two small towns on my way to work. At highway speed it ran around 195 to 200.

When I got to work it was just touching the redzone. I lifted the hood touched the radiator hose above the thermostat and it was hot. Touched the hose below the thermostat and it was cool.

The fan didn't come on when I parked, and the heater worked very well all the way to work. It was very warm, but not warmer than normal.

It sounds to me like an air bubble or a bad thermostat, but from what I understand with these issues the heater will be cold, which mine was not?

I haven't noticed any leaks in the cooling system and I have not had the cooling system open for months?

Any suggestions?

jb

[velozi]

Sounds like the thermostat is not opening. Both hoses should be hot after a long drive.

[rlux4]

The thermostat may not be opening for one of two reasons: failed thermostat or air pocket between the stat and the bottom of the radiator. If you look at the system it is a natural place for air to be trapped, and hot air won't open the theremostat, it has to be immersed in hot water. When you fill the system the water comes up from the bottom of the radiator to the inlet of the stat, air has nowhere to be displaced from there, and with the stat closed, no amount of burping will force the air back down the bottom hose into the radiator where it could rise and go out the filler neck. A very good way to get around this inherant problem is to drill a small (1/8") hole in the valve part of the stat so that air can rise up out of that natural dead end. Like this:

To check if the stat is failed you have to remove it and put it in water and bring it to a boil.
Ron

[HAWKER]

I have been there brother.... I feel your pain....... I have burped several and I have failed and succeeded..... The trapped air in the hose below the thermostat is a problem but trapped air in general, is a problem. The old tech. bulletin about jacking the front of the car so that the top of the radiator is above the cooling jacket of the engine is a must and the engine needs to be run in this position. This is a safety issue as you are dealing with very hot/expanding fluid, so be carful. The trapped air can be relieved another way by loosening the upper clamp on the hose going to the bottom of the radiator and slipping a screw driver down the side of that hose to let the water level come up the pipe to the bottom of the thermostat. Remember to have your heater core open or heat on...
You do need to have a good thermostat. Either check it or pop for a new one and then proceed with the burping fun...

[minimike]

I had an 1800 way back without the benefit of the purge bolt at the rad siamese fitting. It ran hot from time to time
and although I never found out why, probably a bad fit on a hose clamp, what I used to do was put one wheel up on a curb,
warm up the engine with the rad cap off. When the thermostadt opened, you can see the water moving right to left or opposite
in the rad. As the engine reached temp, with the thermostadt opened, I'd rev the engine at the throttle on the cam cover
this would move the water faster. Each time you rev it up the water lever
rises in the rad. This was to get the coolent to circulate and hopefully release any air bubbles.After a bit of time reving, I'd do a final rev. On the final rev, as the water got to the top of the fill neck, I'd slam down the rad cap and twist it to lock.
That would cure the problem for a few months or more if I got all the air out. You have to start with a mostly cold engine to get the cap off with out burning yourself. So basically I used a curb instead of getting a jack out. It saved some time and I
could do it anywhere.