Coolant sensor reads low

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yellow3800
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Coolant sensor reads low

Postby yellow3800 » Wed May 13, 2015 10:29 am

Has anyone put too much goo on a coolant temp sensor when installing it and got a low reading [like a 1/16" gauge needle rise] at normal operating temp?

I have 5 sensors in my parts bin and have tried TWO of them already and in the car, they read low like this.

3.1 v6 is the engine, 1990, Manual trans, where the sensor is right next to the metal cooling pipe [that runs above the front exhaust manifold] under the throttle body facing rearward. Its not the easiest to get to.

my theory is that I put too much goo on it when I shouldn't have. Goo means the typical brown coolant gasket sealer stuff. Its my thought that I inhibited heat transfer to the base metal of the sensor where the threads are. I haven't seen this problem before. Does this sensor need to be installed with clean metal to conduct heat transfer better?

more info: before putting in the sensors, I took a lighter , and with blue [cold] flame, heat up the sensors just to ensure the gauge is capable of a good reading. It is. Wires check good too. Took 15 sec or so of flame, and while hot, it didn't burn me when touching it quickly.

The other thing it could be is a stuck open thermostat, [unverified] but the car shows no signs of that in operation. It appears to be normal [upper heater hose builds pressure when hot].

All sensors give the same resistance readings at various temperatures [refrigerator, normal temp outside and hot from the running car.

There is an off chance that its something else - which is why I'm posting here to see if anyone has crossed this before.

I can't see why trying 3 sensors [2 of mine plus the original] yield the same results.

I hate to pull the one from my 89gt because it works when I have 5 on the bench, though I'll do it as a last resort.

I think thats all I can tell you for now,

Andy



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Re: Coolant sensor reads low

Postby 3X00-Modified » Wed May 13, 2015 10:57 am

yellow3800 wrote:The other thing it could be is a stuck open thermostat, [unverified] but the car shows no signs of that in operation. It appears to be normal [upper heater hose builds pressure when hot].


Just because you have pressure doesn't mean the thermostat isn't stuck open. The pressure will always be there when the coolant gets hot and expands and your cap does what it's supposed to do and holds the pressure in.

The cooling system also flows out of the motor away from the thermostat. Coolant goes into the front of the engine and out the back where the thermostat is and to the radiator, so the upper radiator hose is actually the outlet.



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Re: Coolant sensor reads low

Postby ifixalot » Wed May 13, 2015 12:28 pm

My daughter had a 90 with 3.1. When you drain coolant and put it back in, it can trap air.
If you have air trapped and the sensor is in the air it could read low. Coolant transfers heat much better
than air. Later year cars had extra piping to eliminate this air.
I used to jack the car up on the passenger side so the coolant could move over to the drivers side.
Then I'd loosen the hose clamp at the goose-neck or radiator, which ever is highest and let the air bleed
out by loosening the hose. Some goose-necks had a bleeder on them like a small pipe nipple to bleed air out.
I think I may have drilled a hole in the goose-neck myself but that was years ago so I'm foggy on it.
Also if the thermostat is in air it will take longer to open and the engine will get hotter than it should.
So be sure to get as much air out as possible.



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Re: Coolant sensor reads low

Postby Cliff8928 » Thu May 14, 2015 1:55 am

Does your '90 have digital gauges? If it's analog, that sensor is only for the ECM and not for the gauge. The analog cars (except '96) have an additional sensor in the rear head for the gauge.


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Re: Coolant sensor reads low

Postby yellow3800 » Thu May 14, 2015 9:30 am

nice one Cliff. it is digital. You have graduated from a fountain of knowledge to a mountain of knowledge! Can't put anything past you. Like in the first post, it is capable of the range on the gauge by applying heat to the sensor, key on, eng. off, and watching it climb. Otherwise, I'd not put it past the computer to mess things up. So this should be a direct sensor to gauge signal.

Air eh? Funny this is mentioned because there IS that bleed nipple on the pax side front vertical coolant tube that my 89gt does not have. I didn't use it yet. I somewhat doubt its responsible for a complete 100% of the time low gauge reading. Inconsistency I will believe, yes. What I believe doesn't mean anything one way or another, lol. Dodge rams are horrible when air gets in them - it stops the entire system! This is not reverse flow on our berettas like the ram I recently worked on, so I know it can't be an all stop to cooling if there is a little air.

I haven't thought the thermostat to be it because it builds heat rather quickly, like the standard 2-3 min using conventional engine oil to reach normal temp.

more details I withheld: the previous owner had orange coolant in it! The flush may not have been good or done at all for the current green that is in it now. maybe this means I need to check that thermostat and system for sludge [radiator seems okay when cap is off], bleed the air [injected by me during sensor swap], and re-evaluate.

No one buys the idea of me putting too much thread sealant on the sensor by the look of it.
Okay, good to know. I thought that was reaching anyway! I had previously read [on rockauto's sensor construction description], the difference in sensor construction dealing with the base metal threads and hex having better heat transfer internally than 'other' sensors that need the base metal hot in addition to the probe in the coolant stream. Granted this seems silly for short term. They must have meant long term break down.

Alright, I'll check it out and get back with you!

Thank you!

andy
'90 3.1 manual digital <--problem car
'89gt <---2" vert. crack in front LH cylinder wall for 50k miles sealed with blue devil block seal! compression good!
Lemon <---happy as a clam



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Re: Coolant sensor reads low

Postby yellow3800 » Mon May 18, 2015 3:59 pm

thermostat stuck partially open. This explains why it behaved quite normally, though read low. Its a foreign car to me and 3 other gauges were acting funny from other bad sensors. The car has multiple problems. The new thermostat, a 195F from advance brings up the gauge to 4 bars, though I did see it hit more when idle at a stop after hot. Good enough!

Thank you for the help!



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Re: Coolant sensor reads low

Postby Rettax3 » Sun Jun 07, 2015 9:58 pm

yellow3800 wrote:...got a low reading [like a 1/16" gauge needle rise]
yellow3800 wrote:nice one Cliff. it is digital. You have graduated from a fountain of knowledge to a mountain of knowledge! Can't put anything past you.

Andy, are you testing us? :wink: Somehow this scenario doesn't sound right to me. :no: Glad you can report a fix though...


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Re: Coolant sensor reads low

Postby yellow3800 » Mon Jun 08, 2015 9:10 am

No not a test. I picked up a basket case car that had problems... a beretta rescue from a field actually. Problems started from unplugging the IAC, TPS, AND/or OXY, and the computer not caring. Imagine that one! no ses lights for a change! It just didn't show the ses light after running/driving for an hour! ...which was due to this thermostat problem preventing normal temp from being reached I suppose, and since the car does NOT have two coolant sensors as Cliff responded, I couldn't figure out how the computer knew what temp it was because I'm aware that normal temp is required for the loop to bring in sensor information. I found out BWD vss sensors don't work in my 89gt or the 90gt here, so I got a different brand. Problem solved. I never saw a vss sensor go bad. Well, here is one case. This coolant temp was just a detail in the mess and I've not seen a sensor act up often, so I posted to get a boost in the right direction. Thank you it worked. Everyone needs help on a diagnosis at one point in time and I'm no exception. The thermostat worked on some days, or appeared to, and the engine did get hot enough for the coolant fan to turn on. It wasn't a/c because that doesn't work either.

Now I've all got it running right except for more than normal engine vibration in 5th gear at 30-40mph. my 89gt is smooth, where this car wants to shake like a child banshee. THAT, is a different thread and I may work it out one day because I think its just a matter of ironing it out.

To the unveiling of this problem car: I rescued an indy. Brian Kimmitt/Dantegtz made me do it, lol.

Andy
Lemon <---doing well!
89gt <---2" crack in cylinder wall for 50k miles and keeps going with blue devil block seal treatment [$70/quart!] for perfect gas mileage

'90 Teal indy rescued! <---dig dash, 5spd, 70k miles, undergoing stock paint prep, I'm painting another one! will use freeze 12/red-tek for R-12 on the a/c.




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