dogbite5150

So, as I'm driving 90 mph down the interstate (shame on me), my temp gauge flickers up near the top and then the thing overheated.

I've always noticed the gauge getting up above 100 and flickering around in certain situations, but the car has never overheated until now. In fact, I was about to replace the sender because I thought it was lying to me.

Well, it wasn't lying. The car seems to be no worse for the wear. I never ran it completely dry. Thank God for iron heads I guess.

So.... I figured the thermostat was bad and went to look at that only to find that there was nothing in there. Just enough of one to hold the gasket. Hmm.... Someone has been here before.

The upper and lower rad tanks are hot to warm, so it would seem that the rad is not clogged. The water pump seems to be doing its job. Good heat in the car. Fan and clutch seem solid. I'm sure all the air that made its way in there has caused some of this, but the missing thermostat has got me freaked. Last night I took the upper hose loose and poured about 2 quarts of coolant into it. I'll see what happens now. Ideas anyone?

300Dman

You did not say what area of the country you live in.
Random thoughts:
Just look into the normal causes of overheating. You, know silpping belts, low Coolant level and so on.
You also did not mention if you had a coolant Over Flow Tank.
You can buy an inexpensive Candy or Meat Thermometer at Wal Mart of a discout place and check what the temp really is.
Also coolant will boil sooner if the concentration of the Antifreeze is low or it is very old.

Most likely the prior owner was haveing an overheating problem and removed the Thermostat.
How, do you know none of the Radiator Cores are plugged? Unless they are all plugged there is no way to check that.

If you Coolant Level is low and you have not leaks I would be sure to check you Transmission Fluid if you have an Auto Trans as the Transmission Cooler is inside of the Radiator. If it leaks Coolant goes into the Trans also.

If after you Coolant is filled and clear all the Air out and you have driven the Car up to operating temp and there is tiny bubbles in the Over Flow tank you could have a leaking Head Gasket.

300Dman

If nothing else appears to be wrong you might pull the Radiator and take it to a Radiator Shop and have it Cleand in their tank.

I have mixed feeling concerning putting some sort of chemical flush in to clean out the system. As doing so can distrub stuff that has been there for years and I have seen it tak more than 1 year in 1 case for all the stuff to stop breaking loose. In the mean time It would plug the system up ounce in awhile.

dogbite5150

Thanks for the input. I am in central Illinois USA. It is cold out now, so the weather can only help it cool. I agree the rad could be plugged enough to be ineffective. I think I'll put a stat in it, bleed the system and see what happens. If that doesn't work, I'll look into the radiator.

Is normal operating temp 80c? Also there is a temp sender in the thermostat housing. The wire snapped off on me yesterday. I'll be repairing it, but what is that for? i know the temp gauge sender is in the head.

300Dman

Just saying it is a 123 covers quite a few years.
On mine the sensor for the Temg Gauge is in the middle of the Cylinder Head on the Fuel Injection Pump Side.
Some of the earlier models had a Glow Plug Relay that uses a Coolent Temp Sensor to sense the temp. I think that is the one that you are speaking of.
Look at the Color and if the Wire has a colored stripe and then look at the Glow Plug Socket going into the Relay and see if it has that color of wire on it.