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Overheat light

 
reholmes
I love my Chevy Chevette!
Posts: 1
Joined: 01/13
Posted: 02/19/13 12:26 PM

My 1987 TPI engine runs at a constant and consistent 200 degrees, unfortunately the overheat light comes on at that temperature. Do I have a faulty sensor/sender unit? Would replacing it correct the issue?  

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waynep71222
My first time was in a Chevy
Posts: 241
Joined: 04/12
Posted: 02/19/13 12:55 PM

ok... i have a question.... does the gauge actually work?

shows 70 F at start up.. works its way up to 195 as most C4 corvettes run right around 228F..

this should be for 86 to 89 models..

N5 on the passenger side of the motor is a TU66 for the gauge... should look like this
TU66

this is the Engine Coolant Temp Sensor... ECT... goes in the front of the intake manifold below the thermostat area but sticking straight forward.. below either the smog pump or alternator..
Su102
a capital D on the image below..


N13 is the aux radiator fan switch.. single fan cars may or may not have this.. dual fan cars with 3 relays will..  

Radiatorfranswitch S500sideview
Radiatorfanswtichtopview




8689Componentlocator  

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waynep71222
My first time was in a Chevy
Posts: 241
Joined: 04/12
Posted: 02/19/13 01:06 PM

next...  do you have a 192F thermostat.. and does the radiator fans actually run when the engine comes up to temp???

until i get more.... can you verify that the radiator fan blades have not melted the center out and are failing to operate...


please DO NOT GO PROBING around in the radiator fan relays with a conventional test light... there is one wire that controls the radiator fan relay from the computer that you do not want to probe.. if you do.. you can burn out that circuit in the computer...  

normally the computer turns on the radiator fans with the relay. but the computer looks at the engine coolant temp sensor on the front of the intake with 2 wires on it...

when the coolant gets too hot.. the secondary fan switch in the drivers side cylinder head turns on the radiator fan on single fan cars. or turns on both fans on dual fan cars...  

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waynep71222
My first time was in a Chevy
Posts: 241
Joined: 04/12
Posted: 02/19/13 01:11 PM

this is the 85 to 89 radiator fan wiring diagram on the left side of this page..
out of site on the right is for the 84 crossfire motors..

85 89Corvettecoolingfanwiring  

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Bobs427
I love my Chevy Chevette!
Posts: 3
Joined: 02/13
Posted: 02/20/13 05:01 AM

Just a little FYI:

When you install the sensor, don't use any sealer on the threads. The threads are tappered and should seal. The reason you want a good contact between the sensor and the manifold. If you have to use a sealer use very little. If the sensor comes with it on then itstall it that way....I have seen problems crop up because of a poor connection....

Bob Aka-pepsi1  

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pepsi1
V-6 Camaros rule!
Posts: 88
Joined: 01/12
Posted: 02/24/13 05:51 PM

You want a good ground connection between the sensor and the intake manifold.

Bob  

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lonewolf11
V-6 Camaros rule!
Posts: 105
Joined: 04/09
Posted: 02/27/13 09:20 AM

Icon QuoteBobs427:
Just a little FYI:

When you install the sensor, don't use any sealer on the threads. The threads are tappered and should seal. The reason you want a good contact between the sensor and the manifold. If you have to use a sealer use very little. If the sensor comes with it on then itstall it that way....I have seen problems crop up because of a poor connection....

Bob Aka-pepsi1


Now I hear of this.... Bob, I have used a little of the "Plumber's Tape" on the threads on my Sensor's, AutoZone Part #'s TU66 (Driver's Side) & SW502 (Passenger Side) & SU102 (comes with Pigtail Connector or SU109 without Pigtail- front of Intake Manifold & 1 under the Plenum, same sensor for both) without any issue's. This is in response to your thread about the contact area, something I was unaware of. I mention SU102 & SU109 (again, AutoZone) to the posts here as well. Hopefully our comments has helped reholmes. Of course Wayne has supplied all of the correct diagrams & photos of each Sensor. Another possibility perhaps is item #8 in the Diagram, The Engine Fan Relay, I had to replace mine as well during the replacement of TU66 & SW502 etc.

By the way, reholms, I am running 160 degree Thermostat on my engine as it is no longer stock. Yours being stock, stick with the 192 Degree Thermostat, I believe this is the factory temp for turning on/opening degrees, it's been so long I forget. Wayne, Bob, is the 192 correct? Autozone only lists 160, 180 & 195 Degree Thermostats for my 1987 Corvette.  
Gregorio Lonewolf

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pepsi1
V-6 Camaros rule!
Posts: 88
Joined: 01/12
Posted: 02/27/13 01:48 PM

Lonewolf: Thanks I try to help. But sometime I'm late at the gate...LOL...
 When Wayne helps someone with an electrcal problem I learn from it also. He has the schematics and diagrams. Unless there is something that I really know I don't get involved with Wayne's posts. He is on about 24 Forums possibly more...LOL... I'm on 18 or so and it keeps me busy. I am a senior to most of our forum gear heads. I want to pass on information that can help.
  If you get a chance go to the CHP forum. We found that some Small Block Chevy oil pumps used in drag racing the housings are cracking. We think it's from studder boxes. When the engine is at full throttle and the studder box makes the engine misfire to control RPM.If your interested.
  I apologize for not getting back to you sooner. I have had trouble logging in the last 2 month's. So you may see me in as other login names. I am actually using my 10 year old VAIO and it seems to be Okay.

Well anyway if its working the way it's supossed to don't worry about it. The reason I recommend not using any sealer.Is This:
   My friend has a couple '84's one acted up. I was on a business trip. So he took it to a dealer. A week later he had a problem with the temperature light coming on. Just to prove what I did was correct. I soldered a wire from the side of the sender (sensor) and then grouded it to a good ground post on the intake manifold. It worked perfectly. So I took it all apart and reinstalled it. He said its been fine, for 2 years now...LOL...
  I know that some sensors will come with a sealer of some type on it. If the sealer has a metal base to the compound it will work.
Thanks for the kind words...

Bob  

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waynep71222
My first time was in a Chevy
Posts: 241
Joined: 04/12
Posted: 02/28/13 08:15 AM

sensors that need to be grounded to the engine..


the radiator fan switch. this switch closes the contacts at 238F as i recall.. not variable.. and it connects when closed to the block via the shell
Radiatorfanswtichtopview


the engine temp sending unit..   this sensor varies the resistance to the block to control the temp gauge.
TU66


the engine coolant temp sensor does not need to be grounded to the block..
Su102
this ECT sensor has a varistor inside.. there is 5 volts on one wire.. and what ever voltage the temp variable resistor allows thru on the other wire.. this lets the computer know how hot the engine coolant is...  

i like to recommend the TU102 from AZ or wells as its only a few bucks more than the sensor alone, as it comes with the pigail that sells for as much as the sensor its self.. its a deal..  and the pigtails also fail over the years...

now... i have one more question... has anybody ever seen a sensor like this screwed into the back of the cylinder heads...

1T1065

this is an ENGINE METAL TEMP SENDER/or SENSOR... this again is a switch... they are usually used on caddys... and when the cylinder head reaches a dangerous temp.. like when coolant is lost or the thermostat has locked up.. it will turn on the ENGINE OVERHEAT LIGHT.. that is separate from the gauge .... i have not seen one on a corvette.. but most of the electronics on corvettes are also found on caddys..  

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lonewolf11
V-6 Camaros rule!
Posts: 105
Joined: 04/09
Posted: 03/01/13 08:39 AM

Wayne, on the Sensor that you are asking about being on the back of the heads, the bottom photo you posted, I have never seen 1 of these on my heads in all the years I have had my Corvette. Then again, I bought mine used so perhaps in some prior ownership. But I do not believe this Sensor was on any L98 of my year.

Reholms, are you seeing or have you seen any sensors on the back of your heads?

I agree with you on the SU102 vs the SU109, coming with the new pigtail is not only a smart way to go, it's probably the best way since a Pigtail invariably is needed. BTW, the Pigtail alone (part #254 ~$21.99) costs nearly $7 more than the Sensor (part #SU109 ~$13.99) itself. Buy yourself the SU102.  
Gregorio Lonewolf

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lonewolf11
V-6 Camaros rule!
Posts: 105
Joined: 04/09
Posted: 03/01/13 08:50 AM

Bob, thanks, I too am a member of CHP and will check on this Post/Blog of which you mention. Anything about the Small Block I find interesting. As to the sealant all seems to be fine but keeping a close eye on things will be prudent.

Back to our friend, reholms, original inquire, have you had any success with your overheat light? One suggestion I might make here, and I learned this from my own mistake, be sure to get the TU66 & the SW502 in the correct head. Otherwise you will get some strange readings as I did. Oops, this mistake is made only once.  
Gregorio Lonewolf

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