Hey guys,

I was hoping someone could give me some information on a coolant temperature sensor on an 88. I spent a couple of hours reading through the archives and I'm still not sure of its exact role.

I've noticed a lot of people recommend to check that sensor when people are having a rough idle/hard start type situation, and I saw a procedure to test it without having to replace it. Wouldn't the digital dash show an incorrect reading if this sensor was bad, or does a different sensor control this? It's my understanding that the sensor sends its data to the ECM, and the digital dash gets its reading from the ECM as well.

What I need to know is how it affects fuel delivery and fan operation, and anything else that it does that I'm not aware of.

I'd appreciate any information anyone can add to this.

 

On my 85 I believe there are three senders (someone correct me if I am wrong), one on the front of the engine that controls when to turn the fan off and on, one on the passanger side of the block that sends the info to the ECM, and one on the driver side of the block that sends the info to the dash. To check it unplug the connector from the sender and check the resistance through it. If it is a normal day outside and it hasn't been running it should register in the neigborhood of 2000 ohms. If the car has been running and it is hot, I believe it will be down around 40 or so ohms. How you check the resistance depends on the type of senders that are on your car. The single terminal ones will have to be checked through the terminal to the block, the double terminal ones can be checked through the terminals. The only sender that would affect fuel delivery would be the one that sends the info to the ECM. I have never looked into how it does affect it though, and I don't have my shop manual here to check either.

You may want to make yourself an ALDL to serial cable so you can pull the info of the ECM, I did and it is invaluable.
http://www.winaldl.webhop.net/

Good luck! :cheers:


[Modified by DF, 7:47 AM 6/4/2003]

 

The coolant temperature sender is under the MAF sensor at the front of the block and it supplies information to the ECM so the ECM can control fuel/air. The cluster temp gauge gets its info from a sensor on the right side of the block. The main fan gets turned on by the ECM from info from the coolant sensor under the MAF. The auxilliary fan (if you have one) gets turned on by a thermostatic switch on the left side of the block between cylinders #1 and #3. Hope this helps.

 

This is interesting - I noticed there were 3 temp sensors on my '89 when I had it appart to change my head gaskets, but I never questioned what each did or why. One is on the front of the intake manifold just below the MAF, and the other two are in each of the cylinder heads between cyliners #3 & #5 and #4 & #6.

This is good stuff - keep the info coming...

 

Its funny you ask this now cause the coolant temperature sensor on my 96 JUST went out. i dont know if my LT is the same as your L98 but i know that when my sensor went it was going haywire on the electronic readout coolant guage and would flash eratic numbers. since the ecu reads this and uses that to help run the engine i would get power suges and lags. especially in traffic when i shifted into gear and started to apply throttle it would want to lurch forward and then immediatly lull back. then i disconnected it till i could get another one and it started throwing all sorts of codes and the check engine light came on and the change oil light came on and i started having problems starting it. but as soon as i replaced that 20 dollar peice it fixed all of my problems! hope this helps!

 

L98s and L83s, all have the ECU sensor in the front of the intake manifold. GM swapped sides from year to year on the guage sensor and fan swithch. Good luck, and...

RACE ON!!!
1984 Crossfire
Member NHRA

 

Does this also apply to OBDII '96 cars???

I was thinking about buying the Mid America sensor p/n 609-106 that turns on/off the auxilliary fan at the lower temps. Obviously thats a waste of money if it won't work on OBDII cars.

thanks
dr

 

I recently had a problem where my primary fan would not come on. (84) I could start it by grounding the connection to the switch located on the passenger side of the block. I replaced this switch and the problem was resolved. I do not have an auxiliary fan.... However the fan does not come on until coolant is about 235 DegF. Any thoughts?


[Modified by I40880, 6:18 PM 6/5/2003]

 

A couple. Too bad you waited until you replaced the switch to ask. A lower temp switch will turn on the fan, sooner. Mine comes on at 205 and off at 195. It rarely comes on, though. The other thing I have done, is to install a manual switch, to turn the fan on, whenever I want. It is a great aid in cooling down at the track, between rounds. Good luck, and...

RACE ON!!!
1984 Crossfire
Member NHRA

 

I haven't seen any switches advertised with a temp rating. Where can I get a lower temp switch?

 

I know on my 86 that the coolant temp switch and the fan switch are under the thermostat housing on the front of the intake, but I cannot find the sensor to run the gauge in the car, I dont have any sensors between the exhaust on either side of the block, any thoughts as to were it may be?

 

If you are talking about an 86 Corvette, then I'm not sure if you do know. The front of the intake on an 86 Corvette will house the Coolant Temp Sensor and the Thermo Time Switch for the Cold Start Valve (9th Injector). With regards to fan switch, as already stated in this thread, the primary fan is controlled by the ECM from CTS input, but you made it sound like the two items in the front of the intake were the CTS and a fan switch. This is either incorrect or unclear if by "the coolant temp switch and the fan switch" you meant they are 1 and the same sensor. This whole switch/sensor misuse burns my backside too. A switch is a digital device, either open or closed, 1 or 0. A sensor is an analog device with a continuously varying output across its range. In the case of the CTS the resistance varies from less than 100 Ohms to over 100K Ohms.

As for this, on the passenger side head, between #6 and #8 plugs, just aft of the oil dipstick tube, you don't have a single spade lug connector with a green wire connected, but you have a temp readout on your dash. Is that what you're saying?

 

I do not have a sensor aft of the dipstick, or in the front on the other side. My dash reads LO, I need to know if they did it a different way, or do I need to find the green wire and buy the sensor. Thanks for any help, I would really like to know my temp.

 

Should be on the passenger side head between #6 & #8 on an '86. Hard to believe someone removed it. Maybe someone swapped out the heads and left it plugged? Find the green wire and and obtain a sensor. The wire comes out of the bulkhead connector (behind the battery) at cavity C2.

 

Some of the Corvette specialty catalogs show switches at twice, or more, their value. I got into a sensor catalog and did my own shopping. The major portion of the book shows sensors and switches, by application. You know, a 19xx Xmobile uses an ABC part number. The back of the book had a numerical listing. There were pictures and specs. I selected a switch with the right connecter (from the pictures) and the right threads (description) and desired on/off temps. I think full retail on that switch was about $8.00. Good luck, and...

RACE ON!!!
1984 Crossfire
Member NHRA

 

Hey, there is a green wire running out of a sensor below the radiator hose on the passenger side. Is this the sensor? And if it is, how do I get a replacement as it clips in, or is it the low fluid sensor? I got a check engine light and can not find the OBD port, ripped off all the panels under the steering wheel, and no luck. Then tried to wire the electric fan back up to the black wire/w/ red stripe on the relay, and no such wire on the relay? Any help? :crazy:

 

That is the Low Coolant Sensor.
Which Fan, or do you only have the primary? Are you looking at the right relay? What ever happened to the guage sensor? You really need to work one thing at a time.

 

OK, so I need to find a different green wire in the harness, got it. The radiator fan wasn't hooked up when I got the car, and the car overheated alot, I got it on a toggle switch untill I can get it wired back into the relay, yes got the right relay. Where is the test port, it is not by the steering column as it says in the book.

 

On mine you don't have to move anything at all. It's right there underneath the dash where the driver's side dash meets the center console dash. It basically looks like a black rectangle that you can plug something into.

 

I have been over the hurdles with my 85.

First I bought this 3 years ago. I noticed the fan in front of condensor was never working and of course a.c. didn't blow cold. I replaced the fan. Then I also found a blown fusable link from the battery. And a.c. started working.

My question is to someone who has an 85 with the aux fan... That aux fan is controlled off a.c. head pressure which works fine now. And there is a sensor somewhere that controls this fan if the motor is running hot. Where is this sensor located? I have a very funny feeling that one of the previous owners mis wired this / and / or / installed a lower temp sensor. What is now happening is the fan kicks on at 195 degrees in front of the condersor and being exposed to the outside more than main fan - it is really loud and quite frankly useless if a.c. is not on.

The main fan is on at 228 and off at around 212 which I understand is normal. I also installed a micro switch to run it cooler in heat waves and we can now keep it around 200 in traffic in 100 degree temps with a.c. on.

I have gone to 3 car shows and haven't been able to connect with someone who owns an 85 with an aux fan to ask them. I have poured over the shop manual and cannot find out what temp that aux fan safety is supposed to kick in.

Thanks,

Allen