Something weird with coolant temp
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Joined: Jul 2000
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From: Vancouver WA
Something weird with coolant temp
As with on my other topic about coolant temp readout displaying ''low temp'', I installed a new relay for the fan and drove around hoping that the temp gauge and the rad. fan will work. Unfort. nothing happened as soon as the oil temp reached 180 F, I headed home. As I shut off the car I noticed the rad fan stopping, so I turned the car on (not the engine) and looked to see if the temp gauge worked. But to my surprise it displayed 299 F!!! and a few seconds later the fan came on. About 20 seconds later the temp gauge once again displayed ''low temp''.
Meanwhile the oil temp was around 200 F and before this problem the oil and the coolant were pretty much the same so I assumed that the 299 F was false. And by placing a cooking temp gauge by the hoses and manifold my assumption was correct.
Fortunately the aux fan has been working to keep the coolant cooled so at east there is something cooling the coolant. Now here comes the million dollar question....
Does anyone know what the bloody 'ell is going on with this
:mad
Meanwhile the oil temp was around 200 F and before this problem the oil and the coolant were pretty much the same so I assumed that the 299 F was false. And by placing a cooking temp gauge by the hoses and manifold my assumption was correct.
Fortunately the aux fan has been working to keep the coolant cooled so at east there is something cooling the coolant. Now here comes the million dollar question....
Does anyone know what the bloody 'ell is going on with this
:mad
Thread Starter
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Joined: Jul 2000
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From: Vancouver WA
Re: Something weird with coolant temp (87Beast)
Oh yeah, one more thing. Tomorrow I'm going to buy a GM temp display sensor and if this doesn't work there wil be a free 87 Vette up for grabs
[Modified by 87Beast, 12:14 AM 8/2/2002]
[Modified by 87Beast, 12:14 AM 8/2/2002]
Intermediate
Joined: Aug 2002
Posts: 28
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From: Owensboro KY
Re: Something weird with coolant temp (87Beast)
My 88 has done the same thing. I replace all the sensors and didn't help any either but when I hooked up my scanner the temp. read fine. The only thing i did was make sure I had a good body ground and a fully charged battery and all of it seemed to go away.
Le Mans Master
Joined: Dec 1999
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From: And on the fifth day, subpoenas were served to Obama senior staff
Re: Something weird with coolant temp (87Beast)
It is very possible you have a temp "switch" in place on the passenger side head, instead of a temp "sensor".
If a temp switch is hooked up to the dash, it will read "low temp" when below the turn on temp, and will read full scale when above the turn on temp.
Have you put an ohm meter on that thing yet?
Are you saying that the main fan was working? Did the main fan come on again with the engine off / ignition on, or was this the aux fan?
Fan relay has nothing to do with the temp gauge sensor, btw. You also knew the fan relay was OK as the fan comes on when terminal B is grounded on the ALDL.
You do know that the stock chip in the ecm does not turn on the main fan unitl about 230*?
If a temp switch is hooked up to the dash, it will read "low temp" when below the turn on temp, and will read full scale when above the turn on temp.
Have you put an ohm meter on that thing yet?
Are you saying that the main fan was working? Did the main fan come on again with the engine off / ignition on, or was this the aux fan?
Fan relay has nothing to do with the temp gauge sensor, btw. You also knew the fan relay was OK as the fan comes on when terminal B is grounded on the ALDL.
You do know that the stock chip in the ecm does not turn on the main fan unitl about 230*?
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From: Vancouver WA
Re: Something weird with coolant temp (PeteL)
This could be a switch. I'm going to try out Ray's diagnosis to make sure that the wire is still good - the end piece was disengrated a long time ago and there's electricians tape around the tip to prevent grounding, but this problem never happened before until the Vette was dormant for a couple years and when I change the sensor.
Since I can't tell exactly what the temp of the coolant is, I'm relying on the oil temp to give me a rough estimate. Therefore I don't know exactly when the aux fan kicks on and the main fan.
I decided to replace the fan relay because I had one in stock and the old one had a couple of clips broken off. And as for the fan coming on, it's been a couple years since I drove the Vette but I'm almost sure the main fan came on at 220 F and the aux came on sometime later (I rarely saw the aux come on)
After Ray's test I'll pick up another sensor from a different store to check if there definately was a switch or defective sensor in place.
I'll be back in a few hours (I have to jack up the car to get to the sensor since the headers are in the way).
Seth
Since I can't tell exactly what the temp of the coolant is, I'm relying on the oil temp to give me a rough estimate. Therefore I don't know exactly when the aux fan kicks on and the main fan.
I decided to replace the fan relay because I had one in stock and the old one had a couple of clips broken off. And as for the fan coming on, it's been a couple years since I drove the Vette but I'm almost sure the main fan came on at 220 F and the aux came on sometime later (I rarely saw the aux come on)
After Ray's test I'll pick up another sensor from a different store to check if there definately was a switch or defective sensor in place.
I'll be back in a few hours (I have to jack up the car to get to the sensor since the headers are in the way).
Seth
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Re: Something weird with coolant temp (87Beast)
Theres's always a lot of confusion as to which head the gauge temp sender screws in. GM changed the location depending on the year, so you need to know which head it goes in for the year Vette you have.
On my 86 I had the same problems, the 299 F reading when I installed an aftermaket fan switch. Turns out the 1986 guage sender is installed in the passenger side head, but the instructions that came with the fan switch had me installing the FAN SWITCH IN THE PASSENGER SIDE HEAD.
Prior to installing the aftermarket switch, my dash gauge read correctly, so it didn't take a lot of thought to realize I needed to swap the senders. When I did that, everything performed properly.
One of the mags recently ran an article showing which year Vettes call for senders in which head. I can try to find it if you need the info. In fact, I think I will and post it in the Tech Section since this comes up so often.
Jake
On my 86 I had the same problems, the 299 F reading when I installed an aftermaket fan switch. Turns out the 1986 guage sender is installed in the passenger side head, but the instructions that came with the fan switch had me installing the FAN SWITCH IN THE PASSENGER SIDE HEAD.
Prior to installing the aftermarket switch, my dash gauge read correctly, so it didn't take a lot of thought to realize I needed to swap the senders. When I did that, everything performed properly.
One of the mags recently ran an article showing which year Vettes call for senders in which head. I can try to find it if you need the info. In fact, I think I will and post it in the Tech Section since this comes up so often.
Jake
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Team Owner
Joined: Mar 2001
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From: Cincinnati, Oh USA
Re: Something weird with coolant temp (87Beast)
You definetely have an aux fan switch in place of the temp sender. The temp sender is a temperature variable resistor that operates the dash temperature gauge. Open circuit (high resistance), the dash temp gauge says ,"LO" and shorted (low resistance), the dash temp gauge says, "299 F". The factory aux fan switch turns on at 238 F. On the 87, the dash temp sender is on the right side of the engine between spark plugs 6 and 8. Put the correct temperature sender in and you won't have the funny dash temp gauge readings.
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From: Vancouver WA
Re: Something weird with coolant temp (JAKE)
Problem solved...went out to NAPA yesterday and picked up a coolant sensor for the dash and now I'm getting an accurate reading...life feels good :D . Thanks everyone, and Pete, next time you say something I'll won't doubt you :cheers: . the reason I was putting off that sensor is because I have to jack up the car to get to the sensor and while I was down there I re-tightened the header's bolts (which only a couple needed a 1/16 turn).
Well off to the next problem, talk to ya'll later
Well off to the next problem, talk to ya'll later
Le Mans Master
Joined: Dec 1999
Posts: 8,540
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From: And on the fifth day, subpoenas were served to Obama senior staff
Re: Something weird with coolant temp (JAKE)
The engine was an early 86 that had iron heads when I bought the car.
Glad the sensor fixed the problem, now to figure out why the main fan doesn't come on!
