Peter A.

Hi again guys !
I ordered a new DeWitt radiator the other day, based on a temp gauge reading and obvious crud in the cooling system. Having ordered the radiator, I took some time and gave the system a total reverse flush and refilled with a 50/50 mix. I also purchased an infra red gun because I really would like to get a definite diagnosis nailed down. At idle after 20 minutes the readings are as follows......Bottom hose 187 degrees. Top hose 174. Temp sensor and surroundin area 175. All the while, the gauge is reading 240. This is with a new 160 thermostat.These readings tell me that I'm not crazy, but the gauge is.
Whats going on ?
Peter A.

vetsvette2002

Peter,
1. Since the upper hose is the radiator out hose it should be the hotter of the two.
2. I generally like a 20* difference between engine out temp and the engine in temp - this would show that the radiator is doing its job of rejecting heat.
3. The thermostat's rating of 160* is the minimum operating temp of the engine, once its warmed up with the t-stat open the temp will stabilize above that wherever the cooling system capacity (of heat rejection) allows. You should be running a 180* t-stat, so replace it with the correct rated unit, a Robert Shaw unit would be a good choice.
4. If you've always had an issue with controlling engine temps, then the temp sender is highly suspect, especially given the temps you described. Make sure the temp gun is as close as possible to either the t-stat housing or the radiator goose neck. Same with the engine in temps, be as close as possible to the radiator inlet nipple or the water pump inlet hose barb.

DonO

Powershift

Just search the archives.............this has been an issue for over 10 years that I have been on this forum. Comes up about once every few months. Most likely an issue with the sending unit, although there are also other factors that can affect this temperature (wiring connectors, temp gage, etc). Disconnect the sending unit lead and hookup a multimeter to the sending unit connection and ground potential (battery -). See what the resistance reading is at your 175 F operating temperature.

I question your radiator bottom hose temperature..........usually the temps go DOWN not up as the coolant flows thru the radiator. Various materials (hoses, metals, etc) radiate heat differently and this can cause variations with an IR gun....especially if it is a low cost version without ability to change the emmisivity factor. The IR gun can also pickup other nearby heat sources if you are not careful when using it.

The new Dewitt radiator should cure any heat issues, but I agree the temp gage also needs some attention.

Larry

Peter A.

So,,,let me get this straight. The reversed hose readings are indicating poor radiator flow, and the reading difference between the temp sensor and the gauge are indicating a wacko gauge. Is this correct ?

Powershift

NO. The reversed temperatures indicate you are not getting the correct/proper readings. The radiator does not generate heat. You need to measure more carefully at the bottom (inlet to the water pump).

The reading difference in the gage and IR gun are probably due to the engine temperature sensor...........although the gage could be bad/defective.

Larry

65GGvert

The gauge is the least likely to be defective. The sensor at the intake is famous for incorrect resistance causing the gauge to read wrong. Did the temp ever read correctly before with this same sensor? Unless there's some way the water pump is pumping in reverse, you can't have higher temps on the bottom hose than the top.

Peter A.

Thanks Don and Larry for the quick response. I'm in the garage right now. Going to check the wiring to the gauge, and resistance as suggested. I purchased this car about two weeks ago. Got in it and drove 600 plus miles to the house with not so much as an engine stumble between gas stations. I agree that a new radiator is a good bet for any hot running issues. I suspect that will find a grounding issue with the temp gauge. Just as I did with the clock.
Thanks again. I will post my findings.
Peter

65GGvert

The gauge has 12v on one side and the sensor at the intake is a thermistor that decreases in resistance as the heat goes up. That variation not being in the correct range is very possible. I bought a TU5 sensor at autozone that was right on for about 10 bucks.
If you disconnect the temp wire from the sensor, the gauge should go full left, if you short that green wire to the engine (manifold, ground, etc) the gauge should deflect full right.

65GGvert

The only ground for the gauge is through the sensor mounted in the intake manifold (that has the green wire attached) There is no ground in the dash for the temp gauge.

leif.anderson93

This is the FIRST thing I would do after having taken the temp readings with your IR gun that you have done. $10 and about five minutes of labor and I bet your "problem" is solved

Peter A.

I found that the previous temp readings on the hoses were do to operator error. I did it again ( after reading instructions ) and got 185 at the top , and 178 at the bottom. Still needs radiator ! as for the gauge reading so high, I found that when I installed the new sending unit ( from autozone ) I put way too much teflon tape on the threads I guess that the tape kept the sender from grounding. Cleaned off tape and used Permatex. Seems to be working OK. After 20 minutes of idle, the gauge reads 190. I will have to wait for the new radiator before I can expect lower operating temps. Thanks everyone.
Peter

mhanley

Do not put tape or sealer on the temp sender as this may prevent a good ground. The threads are designed to cut into the intake to give it a good ground. I think your gauge is fine sounds like it was the temp sender. Also don't expect much of a lower temp reading with that new radiator, 170-190 is about normal. Look at using Zerex G05 anti-freeze as it will help prevent an scaling in the new radiator.

Mike

leif.anderson93

If you're idling for 20 minutes and the gauge and the IR gun at the sending unit are both 190, I don't see where you think you have a problem. Don't know the ambient temp outside when you conducted this test, but most here would be jumping for joy with 190 after idling for 20 minutes. As far as the Teflon tape, any amount would be too much...no tape on threads

Powershift

I also would not put TFE tape on the threads, but would use Loctite 565 Pipe Sealant with teflon instead. HOWEVER, both JohnZ and Buns have conducted and documented tests on this forum that showed that a reasonable wrap of TFE tape would not affect the sender unit performance. The archives and FAQ have these tests and the pics to go with them.

Larry

Peter A.

When I drove from southern to northern Ca through the valley , the outside temp was approx. 100 degrees. The temp gauge never went higher than 180. It even dropped going down the grapevine. Several days later, I was driving to town in approx 90 degree weather and the temperature started climbing going up a long grade. It got to around 225,when I turned around. It did not lower going down the grade, and stayed at that temp all the way home. Thats how I ended up finding crud in the cooling system. I would feel a lot better with an operating temp of 180 than a fluctuating temp to 190 or 200.

buns

Will this make you feel better?

.

.

Peter A.

[QUOTE=buns;1590167651]Will this make you feel better?
Yes it certainly does. But while you're watching your gauge climb to 250 degrees, you have ( in my opinion ) taken many years of happy driving miles out of your engine. Watching your gauge go that high can and will cost you a lot of bucks ! But all kidding aside, I would rather play it safe than sorry. I start getting concerned at around 200 degrees, especially when the engine has run in the heat for a long trip,and not gotten hotter than 180. Something is going on !
Thanks for the information,
Peter
.