Temp sending unit reading weird

pirotec354 · Jun 4, 2009

Alright guys well I finally got my car back together after working on it for almst a month. The problem I have now is that the temperature guage does not read properly. I have an autometer guage and it always worked fine before, but now if I turn the key to the on position it will read 150 degrees with the engine stone cold. Ive tried three different switches and have had the same results. I hooked the sender wire to my tranny temp guge and it did the same thing so I dont think the temp guage is the culprit. Anyone have any ideas on what cold be going on?
Thanks
-Justin

HISSIN50 · Jun 4, 2009

So two different temp gauges and multiple senders all have the same reading when cold? I think so. Check your sender wire for a partial short to ground. Grounding the wire makes the gauge read higher.

Also check continuity between the sender body (not where the sender wire goes, but the the flats you tighten the sender with, for example) and the neg battery terminal. It should read less than 5 ohms. Sometimes you have to manually ground the sender housings.

pirotec354 · Jun 4, 2009

Thanks hissin, ill check the wire for a possible short to ground somewhere. I tried manually grounding the wire earlier and it pegged the guage all the way to the hot side, Is there another way? Or did i do it wrong? I went from the body to the neg battery terminal with a wire just to ceck it. And checking continuity, do you mean go from the body of the sender and to a good known ground with a mm? Thanks again

HISSIN50 · Jun 4, 2009

Continuity check for the grounding of the sender body: Set your meter to low scale Ohms. Put one lead on the flats of the sender and one lead to the neg battery terminal. Look for less than 5 ohms.

Checking sender wire for short to ground: disconnect both ends of the sender wire (at the sender and at the gauge). Set your meter as listed above. Put one lead on one end of the wire and ground the other lead. The reading should be infinite (huge) since the wire should not be touching ground unless it's partially shorted somewhere. Now reconnect both ends of the wire and retest. It should still read infinite.

Venom351R · Jun 5, 2009

mine does not do that but for some reason after driving the car for a few mins the temp shoots up to 210 then back down to 180 after another min. It will get to 210 but only when in traffic and when its really hot out, when its been doing that it has not had those conditions. Any ideas?

HISSIN50 · Jun 5, 2009

Redline_351R said:
mine does not do that but for some reason after driving the car for a few mins the temp shoots up to 210 then back down to 180 after another min. It will get to 210 but only when in traffic and when its really hot out, when its been doing that it has not had those conditions. Any ideas?

The sender is in the stock location?

When this happens, is the car really at 180 or 210 or is it really a lot colder?

pirotec354 · Jun 5, 2009

Ok I did some testing, here are my results: Sender wire to negative battery terminal reads 0 ohms from both sides of it. Top of sender to intake manifold, read .433 k ohms.From top of sender to base of sender, read .433 k ohms. From top of sender to negative batt terminal, read .433 k ohms.

Also should the one prong comming out of the top of the sender be able to spin? Bc the last two that ive gotten have been able to spin.

Adam95GT · Jun 5, 2009

HISSIN50 said:
The sender is in the stock location?

When this happens, is the car really at 180 or 210 or is it really a lot colder?

Yea.... this seems like its b4 the tstat... or something weird

pirotec354 · Jun 5, 2009

Alright well i let the car warm up for about five minutes and the guage read 250 degrees, well I took the sender out right after I shut it off and shot an infrared thermometer at the coolant. It read 155 degrees. Im really out of ideas, i dont know what it could be. I guess ill try running a new wire for it to see if that helps, oh and by the way i just bought a new sender again just to rule that out.

HISSIN50 · Jun 5, 2009

pirotec354 said:
Ok I did some testing, here are my results: Sender wire to negative battery terminal reads 0 ohms from both sides of it. Top of sender to intake manifold, read .433 k ohms.From top of sender to base of sender, read .433 k ohms. From top of sender to negative batt terminal, read .433 k ohms.

Also should the one prong comming out of the top of the sender be able to spin? Bc the last two that ive gotten have been able to spin.

The sender wire sounds like it's shorted. Testing from the sender wire to the neg battery terminal or any ground should have read infinite.

pirotec354 · Jun 5, 2009

HISSIN50 said:
The sender wire sounds like it's shorted. Testing from the sender wire to the neg battery terminal or any ground should have read infinite.

Yea i thought that might have been the case so I replaced that wire and its still doing the same thing. Its an autometer guage with a stock sender, will the Autometers only work with an autometer sender? I also tried a different ground for the guage itself and also had the same results.

HISSIN50 · Jun 5, 2009

pirotec354 said:
Yea i thought that might have been the case so I replaced that wire and its still doing the same thing. Its an autometer guage with a stock sender, will the Autometers only work with an autometer sender? I also tried a different ground for the guage itself and also had the same results.

Yes, you have to treat brands of gauges and their senders as married pairs. Install the AM sender (you might need an adapter) and the issue should be fixed.

pirotec354 · Jun 5, 2009

HISSIN50 said:
Yes, you have to treat brands of gauges and their senders as married pairs. Install the AM sender (you might need an adapter) and the issue should be fixed.

Alright well I got an autometer sender and it fixed it, BUT now my car is running hot. Its ~ 220. It usually would run ~ 190 all the time, i have a 180 degree mr gasket thermostat in it. I think i heard those are bad? Ive been trying to get all the air out and im not sure if its working. When i turn the car off I can hear air moving around, like how it sounds when its running hot.

I took a infrared lazer to it afterwards and the upper radiator hose will be at about 190 and the lower will be at about 98 degees. The thermostat housing is about 223 degrees and the lower intake manifold is about 214 degrees. Is this normal or do you think my thermostat isnt opening?

HISSIN50 · Jun 5, 2009

Some folks have had issues with the Mr G t-stats it seems.
Did you change the stat from before when it ran at 190*?

Does it run hotter while stationary or at speed?

Does the fan come on with the AC being on (or at 216*F without AC)?

pirotec354 · Jun 5, 2009

HISSIN50 said:
Some folks have had issues with the Mr G t-stats it seems.
Did you change the stat from before when it ran at 190*?

Does it run hotter while stationary or at speed?

Does the fan come on with the AC being on (or at 216*F without AC)?

Yea I changed the stat. It runs hotter at speed. And yes the fans are working correctly

pirotec354 · Jun 5, 2009

oh and another thing i noticed when i went back out to look at my car. It was still hot and I popped the hood and the upper radiator hose was sucked shut like there was a vacuum on it. Never seen this before, anyone know what could cause that?

HISSIN50 · Jun 6, 2009

Replace the t-stat.

pirotec354 · Jun 6, 2009

Alright I replaced the t stat with a stant 180 degree and it runs cool now, should have never went with the mr gasket. Thanks hissin
-Justin

Venom351R · Jun 6, 2009

HISSIN50 said:
The sender is in the stock location?

When this happens, is the car really at 180 or 210 or is it really a lot colder?

Yeah the sender is in the stock location. IT seems to stay stuck at 100* where the gauge starts then it shoots up to 210 then back to 180 but it never really seems to be at 210 until its driven for awhile.

HISSIN50 · Jun 6, 2009

Redline_351R said:
Yeah the sender is in the stock location. IT seems to stay stuck at 100* where the gauge starts then it shoots up to 210 then back to 180 but it never really seems to be at 210 until its driven for awhile.

If it fluctuates faster than seems reasonable, burp the system some more and makes sure the level is topped up.

Otherwise, I'm not thinking of anything great (if the issue is that it acts weird till it gets hot and then it settles in at 210 and functions normal thereafter).

If the temp reads weird anytime below 210, I'd wanna check the stat.

Justin, glad to hear it's fixed. I used to be a huge fan of Mr G stats (I still am a big fan of balanced stats, which the Mr G is). I should see if we can find a new source (I have the feeling a lot of the balanced stats come from the same factory and just get different packaging put on them).

Temp sending unit reading weird

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