As the engine warms up the temperature gauge goes up to 220 fine but then starts to move towards the red. Some times it stays in the red or slightly below it while I am driving and then suddenly drops to 220 again. The needle also vibrates quite a bit. It keeps going between 220 and the overheat mark. Just to be sure I checked the engine with an infrared thermometer and it reads about 220. The air dam is all intact and the coolant is flowing. I think I will replace the Temperature Sender and see what that does. Are these easily got? are they used on other GM cars? I live in Ireland so I will have to mail order it from the USA.

 

make sure the thermostat isnt sticking closed or partially closed. that will cause high temps like that. this is most likely the cause, or if the coolant is really dirty, something could be plugged up in the system.

 

I replaced the coolant and flushed out the system a year ago. I checked the hoses at the radiator at they are hot so i guess coolant must be flowing. When I am driving along the needle goes to overheat and then suddenly drops to 220.

 

That sensor on the 3.1 is on the left head, up front. Kinda behind the AC and power steering. I belive it requires a deepwell 19mm and can sometimes be pita.

When you flushed it, did you install a new t-stat and cap?

Mine hardly ever sees 220, if it does I'm freaking out like But thats what a 185 and dual toggled fans does for ya

 

ops, just read yours is an 82 carbed 2.8. I have no clue where that sensor would be and what it requires. Sorry for my babble

 

I'm with Dale... if mine hits 220, I'm pullin' over - don't feel like dealing with warped heads, blown head gaskets, popped freeze plugs... etc...

Go to Autozone, and rent the Radiator Pressure Tester. It'll pressurize your cooling system.

Also, next time you're running 220+, shut the car down, pop the hood, hop out, and listen for any 'steaming' sounds... (I can't think of the word I'm looking for, lol!) Hissing! That's it... listen for hissing sounds.

You should hear the radiator bubbling into the overflow tank, that's normal for coolant at 251+ temps (we've got a 13lbs cap, right?)

If you do NOT hear ANY bubbling, even after 30-45 seconds, then you are probably NOT overheating.

In that case, let car cool down, pop off radiator cap (WHEN COOL) then top off the radiator. Crank the car up, pop a thermometer into the cap's spot, and measure the coolant temperatures. When the thermostat opens (you can tell, the temp gauge will go up and up, then suddenly drop down, as well as seeing the coolant move in the radiator) top off the radiator again (have some 50/50 handy for that part) and see what the temp of the hot coolant is. Put the radiator cap on, and compare to the temp the gauge says.

Easier way, is to get a cheap $15 Autozone (Sunpro) Mechanical temp gauge, and see if it reads like yours does.

If the gauges are accurate, and you ARE overheating, look for ANY coolant leaks at all. Freeze plugs, hoses, etc... See if you are blowing any white smoke - that's a blown head gasket, more than likely.

 

Thanks for the information guys. The Sender unit seems to be the same as your Dale from your description of its location.

 

I will go through what you described Doward and see if it's overheating or just the gauge. The engine when I got it would heat up to 220 and stay there all day. My car as Dale stated is a 2.8 with a carb and the fan driven off the engine.

Thanks.

 

Also I live in Ireland so I can't can get a radiator pressure tester from Autozone. I will have a look round an auto shop here and see if I can buy one.

 

Lets see, now that im awake.

It has mechanical fan, that may be not working right.
Replace the cap and t-stat if you havent lately.
Them engine sensors are not expensive (over here anyway). And are plentyful. If you have problems finding one, contact me and I will see if I can help you.

 

Thanks Dale, I will try what Doward suggested and see if I truely do have an overheat problem.

Thanks.

 

I checked the engine and I don't have a cooling problem. I carried out the steps Doward described and the cooling system is fine. I also measured the engine temperature with an infrared Thermometer and it reads 175 degrees. I check the gauge and that reads 240 plus. So the next step I guess is to replace the sender unit.

Thanks.

 

Cool; glad to hear it's not the motor! Does anyone here have the specs handy for that sender? If the infared temp sensor (very cool by the way- I'm jealous- I want one!!) shows 170, then you should be able to put a meter across the gauge's sender and see the correct resistance for 170 degrees.

If it's the correct resistance then there might be either a short in the wire to the gauge, or the gauge is bad...