Shurshot

Hi

My temperature gauge is giving me a hard time.

For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)

Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)

As always suggestions are appreciated

Thanks in advance

Doug

kenba

[QUOTE=Shurshot;1563138103]Hi

My temperature gauge is giving me a hard time.

For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)

Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)

As always suggestions are appreciated


Check the wire to the sending unit. It could be correded or the clip may not be making contect all the time. usuely It's a ground wire somewhere if the guage & sending unit are OK.:cheers

MikeM

I'd try another sending unit. I believe they work off a variable resistance to ground and it sounds like your ground is a little inconsistent.

Pierre

Make sure you don't use any teflon tape or other sealant on the sending unit. That would have an impact on a clean path to ground.
Pierre

Shurshot

I have tried two different slip over ends with no change so the bad unit sounds like a good possibility...... Ironically on this one (just got it from Rogers clocks in Tenn.) I have no sealant but on my original intake that I just took off a few months ago I can see some sealant in the threads. That one worked consistently although it read about 20 degrees high and was why I bought the new one from Roger

Between the thermostat housing and shape of the Brodix intake I am now using I can't get a level grip on the sending unit to remove it so changing the thermostat idea just got a lot better. I am going go ahead and do that and get the sending unit out at the same time. Then I will put my old one back in and see what happens.

I have heard that there are "adjusting devices" available to calibrate the temperature reading........ still a pain but as long as I can be consistent and not erratic I will be happy.

Thanks for the replies and I will post the result with the old sending unit installed.

Doug

MikeM

Ground the sending unit wire to the manifold. It should peg the guage hot and stay there. If it does, change the sending unit.

JohnZ

Conversely, if you just disconnect the wire from the sender, the gauge should peg to full cold.

Shurshot

Well it does do that but something is certainly not right. I tried to get my old sending unit out of the L72 intake but with no success.

I don't suppose my chances of getting another "correct" sending unit locally are very good but I will try to in the AM. I did not like the thermostat housing gasket I got from NAPA and the replacement for my broken hood latch cable is not here yet (but it has been shipped) so I still have some small stuff to acquire and get right while I look for another sending unit.

Thanks again for all the replies

Doug

Vetterodder

That was the problem on my `65. The guage acted just like Shurshot's but problem solved when I removed the teflon tape.

65 vette dude

I had the same problem with my gauge reading 15 to 20 degrees high. After trying two more sending units without success,I took the advice of a couple of members and went to Autozone and bought a Wells tu5 sending unit. That did the trick. Gauge now reads right on the money.

Shurshot

I guess I will try that route

I put mine back in along with a 180 thermostat...... now it reads 20 degees low (160) but is no longer is moving around on me........ go figure

Doug

MikeM

Are you by any chance using an open end wrench to R&R that sending unit?

Shurshot

On that one I used a 3/4 deep socket (15/16 if I remember right) but on the old L72 intake with a sending unit that worked fine I tried everything but it would not budge

Why do you ask?

MikeM

I gotta' be careful because I've never cut one of these sending units apart to see how they're made. I've seen them damaged, as in egg shaped by pulling on the flats with an open end wrench. What this does to the internals of the sending unit, I don't know for sure but I always heard it's easy to damage one to the point they won't work.

In you case, I believe you said the guage needle would go all the way to hot for no reason. This would indicate a dead short in the circuit. Then, again for no reason, the needle would swing back toward cold. So, something is causing the "sender" to send erratic signals to your guage.

If you had a problem with sealer on the threads preventing the sending unit from grounding, you'd tend to get a colder/lower/no reading on the guage.

Whether the guage is accurate or not, it should at least be steady and consistent. That's why I think you have a defective sending unit.

magicv8

Keep the wire to the sender off the hot engine. I wrapped mine with aluminized tape over the cloth insulator.

If the wire insulation touches the intake at the exhaust crossover area, it transmits 600F exhaust heat to the sender fast.

Shurshot

Hi Mike

I just put a new one in from autozone so we will see how it works out in just a little bit. There is a 'racer guy" that works there and he seems pretty sharp on some things. He thinks because of a closed system on my car that I have been having an air pocket problem that was causing a spike in the reading......... sounds reasonable to me but who am I.

The new unit cost a whole 5.99 and hopefully I will not have to go back in and put a new thermostat gasket on (had to take it off to slide the socket over the sending unit.

Doug

MikeM

I would think an air pocket would give you a downward spike in the temp. Not up.

I hope your new sender fixes your problem.

Shurshot

Well the new one would not seat right so it leaked

Just so I could drive it today in the good weather I put the old one back in

Kinda of a pain having to remove the thermostat housing every time I do this but I was able to find the unit recommended by "65 vette guy" while driving around today (Wells TU5) as well as a reusable thermostat gasket.

So I have hope for the morning and time to check it out before the weather comes in that we are expecting here to tomorrow.

Thanks again for all the replies

Doug

FrankWJones

I had the same problem in my 66 with the 327/300. I would be cruising down the road and all of a sudden the temp gauge needle went full movement to the right or to the extreme "Hot" position. I corrected this by inserting lock washers between the gauge and back panel on the mounting studs to ensure gauge was actually bonded to that panel. From there, i installed another wire from the back of the panel to a suitable ground. No more off scale high readings. Gauge appears to function normal..

Frankie the Fink

11 year old thread - I'm betting the original poster either sold the car or fixed the problem...