Yesterday I had some issues with overheating. Usually my car runs around 200°F in city traffic and goes up to 210°/220°F at Highway. Yesterday at around 70 mph it ran up to 240° pretty quick and cooled back to around 220° within seconds.As I reached the next city it was back at 200°. After leaving city it began raising again between 220 and 230 but cooled down sooner, but I had to reduce speed due to traffic situation. Back home I checked coolant level which was good and there were no signs for boiling coolant. Even overflow hose was dry.

My bet is a weak thermostat, but I would appreciate any ideas from the pros out there!

Here are some facts about the car:
69 cutlass 350 factory A/C but deleted; everything else was left as with A/C
fan clutch is new
I am not sure about antifreeze/water ratio, but antifreeze hydrometer shows -15°F, thus ratio should be around 50:50

Thanks for any help!

Greetings from Germany

 

When I squeeze the hose I can feel the spring. But it just reaches until the hose bends, so there are about 5" before the water pump w/o spring.
_____
Andi

 

I'm not sure what you mean by a "weak thermostat", but there are two failure modes. If the t-stat opens prematurely, that won't cause over heating. I have, however, seen t-stat failures where the expanding capsule part of the t-stat failed, causing late opening, which would be a possible cause of your problem. Other possible causes are a partially blocked radiator (I've also had this happen) where crud blocked the lower 1/3 of the radiator and the collapsed hose. Other things to check are your advance curve (not reaching full mechanical advance) and carb jets (secondary jets might be blocked or restricted, causing lean running at spead).

 

That is definitely on the warm side for a 350, even your normal running temps. Those are more like 403 temps. I would get a 180 or 195 Stewart Warner modified high flow thermostat. Then I would flush the cooling system, maybe even a double dose for a day or two driving and see what comes out. When you drain pull the block plugs too.

 

I would replace the thermostat with a 180 degree Stant Superstat. Flush the radiator and replace coolant. It could also be as described by Joe, a severely clogged radiator that may require a radiator shops assistance to chemically clean, disassemble, and rod it out.

 

Thanks for all the help!

joe_padavano,
yes I was thinking about a late opening thermostat.

I took the car for a ride today and it was about the same. Around 200° in the city, on highway it first dropped to around 190° (IMO because of higher airflow) and then went up to around 230°. It cooled then down to around 200° with me doing nothing. So I would stick to the theory of a late opening thermostat.
I don't think it would cool down without reducing speed if it would be a blocked radiator or a collapsed hose, would it?

I just ordered a 180° Superstat thermostat, not from Stant but from Gates since it is available around here. I will also change coolant and flush radiator when changing it. Let's see if it helps.

olds 307 and 403,
I would not expect the car to run cooler then around 200° with a 195° Thermostat, would it? It will allow the coolant flow through the radiator beginning at 195 +/- 5 and is fully open at around 210. Then cooling down to 185 or so until it closes and coolant will heat up again. Am I wrong about that?

This car really gets me used to US units

Thanks again

----
Andi

 

It might be more then a bad t stat, I'd take a long look at the radiator.

 

Make sure your timing is correct. I had a similar problems before I got the timing 0'ed in.

 

I would agree. Other things are possible, but that's your #1 likelihood right now.

Be sure you have an extra thermostat gasket (or two) for when it doesn't seal the first time.

- Eric

 

Thanks to everybody...the new thermostat fixed the problem! Temp does not exceed 190º at any driving condition!

The old one also was a 180º thermostat. It did not move at all when I put it in boiling water!

Great Forum!

---
Andi

 

Just like it's supposed to work.

Glad you got it fixed!

- Eric

 

Well done