Wacky Coolant Gauge

[c3po]

I have a small block chevy in my 1983 Chevrolet El Camino that has the coolant sensor mounted in the driver's side cylinder head.

I recently put on a 195 degree thermostat, and I made sure it was working properly, obviously the coolant temp in the cylinder head should be higher than the temp in the intake manifold by the thermostat housing.

My coolant gauge is reading between 180 and 185 degrees, but when I aim the infrared gun on the coolant sensor in the block, I get a reading of 210 degrees.

I was thinking maybe I need to take this coolant sensor out and clean it because there could be some junk on it.

The other thought is maybe I could put on a mechanical water temp gauge and run the sensor to a port in the intake manifold.

This car has 367,000 miles and it is 26 years old, so maybe this gauge in the dash has seen better days, maybe I can take the wire off at the sensor and clean the metal piece that the wire goes over.

I know the car is not running cool since when I put my hand on the upper radiator hose it is very hot.

I am running a 7 pound radiator cap, since this engine is old and I do not want to blow a head gasket, would a higher pressure cap give me a faster warm up time, or is this not the case.

Any advice would be appreciated.

 

[Chris142]

Originally Posted By: c3po


I am running a 7 pound radiator cap, since this engine is old and I do not want to blow a head gasket, would a higher pressure cap give me a faster warm up time, or is this not the case.

All a higher pressure cap does is raise the boiling point. Has nothing to do with how fast it gets up to operating temperature.

Adding more pressure does not make the engine run cooler which is what 99% of my customers think.

With your 7psi cap and at sea level your engine will boil over @ 233F. With a 13psi cap it will boil @ 251F.

If your engine is 220F it will be 220F with 7 or 20 lbs pressure on it.

 

[Ignatz]

One thing... If you take out a sensor to clean it....I'd put a new one in. Those wires that go to the sensor on the head get brittle and might need to be replaced. If your worried about the head gasket, maybe go to the next cooler thermostat. I know, I changed my thermostat on my 92 Astro cargo van to a 195, and it seems to go up a lot further on the temperature guage before the thermostat opens and then settles half way on my temp guage. I use standard caps and make sure the anti-freeze is fresh. Its not your fault if the head gasket goes on a car with those miles!

 

[c3po]

Where would I pick up a new coolant sensor to screw into the cylinder head.

 

[GMBoy]

Originally Posted By: c3po
Where would I pick up a new coolant sensor to screw into the cylinder head.



Any auto parts store or dealer.

Add to the thread, you may want to drop down to a 180 thermostat. I did that with my old 1978 Jeep CJ and it offered the best overall compromise. Stock was 195 with 180 and 160 being offered aftermarket. If you are aiming a laser thermometer at the block near the sensor to test the coolant temp you;re probably getting heat soak from the manifolds so inside the coolant passages it really might be 180-185.

 

[c3po]

My coolant sensor is near my shorty headers, I do have them Jet Hot Coated, so I might not be getting an accurate reading.

I went to a 195 thermostat for a few reasons:

It is very cold here in my area.

I have a 6 quart oil pan, with a trap door, crankshaft scraper, windage tray, and a oil pump baffle.

I also do not have A/C so there is no condenser up front. So nothing is obstructing the radiator.

I did 2 applications of auto-rx, which is allowing oil too get everywhere in the engine.


I can drive this car for an hour, and then come back 45 minutes later and the temp gauge is at the cold point when I start the car up.

I was running a 180 thermostat before auto-rx and when I went to change my valve cover gasket there was a little bit of gooey oil, kind of like a paste in the cylinder head, my thinking was the engine was not getting hot enough to prevent this.

 

[demarpaint]

Didn't the stock T-Stat housing have a provision for the coolant sensor? It's been a long time since I've looked at a Chevy, but my Fords have the sensor in the T-Stat housing. The headers are probably throwing things off a bit, and perhaps its time for a new sensor.

I would leave the thermostat alone and not go to a lower temperature. As mentioned above the 7 lb cap just lowers the boiling point of the water. In a car that old I'd stick with the 7lb cap.

Cars cool off fast in the cold weather, so 45 minutes later you'll get a cold reading, but the engine is going to warm up faster than it did first start of the day. YMMV

 

[GMBoy]

Originally Posted By: c3po
My coolant sensor is near my shorty headers, I do have them Jet Hot Coated, so I might not be getting an accurate reading.

I went to a 195 thermostat for a few reasons:

It is very cold here in my area.

I have a 6 quart oil pan, with a trap door, crankshaft scraper, windage tray, and a oil pump baffle.

I also do not have A/C so there is no condenser up front. So nothing is obstructing the radiator.

I did 2 applications of auto-rx, which is allowing oil too get everywhere in the engine.


I can drive this car for an hour, and then come back 45 minutes later and the temp gauge is at the cold point when I start the car up.

I was running a 180 thermostat before auto-rx and when I went to change my valve cover gasket there was a little bit of gooey oil, kind of like a paste in the cylinder head, my thinking was the engine was not getting hot enough to prevent this.



Based on your climate, you are right - the 195 is a better choice and I did run the 195 in my old CJ7 when I used to live in Maryland (for 35yrs) so I could have heat. Changed to the 180 when I moved to Texas 5 years ago.

 

[NYEngineer]

The sensor in the intake is an electric fan switch in later model cars. The one in the left cylinder head is the gauge sender.
Don't panic too much about the difference between the gauge and the infra red gun. That gun is showing you the surface temp of the iron, not the coolant inside. Those things take practice to understand correctly.

 

[meep]

I don't think you have a problem... prolly overthinking in this case. Gauges are better for trending than specific numerical readings. Engines fluctuate in operating temps and will have temp variations depending on location to some extent.

I'd stick w/ the 195 stat. If you are nervous, pull the hoses, grab a garden hose and flush the grit and grime from the cooling system, heater core, etc..

Temp sensor may be suffering ground connection. Folks say that using teflon tape or other sealants can give false readings, but I've HAD to use these things to prevent leaks and haven't had any trouble -- it's a miniscule amount of power going through that cnnxn.

Good Luck,

M

 

[demarpaint]

Good point about the Teflon tape, I've read it interferes with readings from electrical gauges. IIRC it interferes with how they are grounded to the block. Besides the only accurate gauges are mechanical, all a dash gauge is, is a glorified idiot light.

As I mentioned above leave the 195 T-stat alone, or you'll create a new set of issues.

 

[c3po]

I did flush out the cooling system when I put a new radiator on in the fall.

I also do not have a heater core on this car, I think that I will just drive this and when the weather gets warm I will think it over then.

I need to go out and blow some snow with the Snowblower, it's only 19 degrees outside, that's a little bit cold for my area.

 

[eljefino]

How does the coolant flow on a classic SBC? Through the block and up thru the heads, then the IM and out the thermostat housing? If so it would get hotter as it travels up in the motor... maybe.

I had a dodge 2.5 where the gauge sensor was a significant distance from the thermostat and it acted oddly... when I really got on the motor going up a hill or whatever the indicated temp would go DOWN... finally figured the thermostat was opening more making the coolant going in the other side COLDER which the sender was picking up.

If you need room for more taps and sensors you could probably find a different SBC thermostat housing "gooseneck" with more taps; real ugly inelegant things from the smog years.

Incidentally is there a computer in this thing with its own thermo sensor seperate from the dash one? Might be fun to stick a scan tool on and see its reaction. Conversely you could stick a digital ohmmeter on a two-pin computer sensor and look the temp up on a table you can find online.

 

[NYEngineer]

Yeah. The coolant goes through the block first and heads second on your small block.

 

[c3po]

There is no computer in this thing.