Engine fan inoperative
Thread Starter
6th Gear
Joined: Apr 2010
Posts: 6
Likes: 0
Engine fan inoperative
the cooling fan on my 89 vette will not start at all when the car runs, causing overheating of the engine. when i ground ckt 335 and the fan runs. i replaced the relay and the fan still does not start when the car is running. i probed the ign on the connector and it was ok as was the main battery. When i jumpered A and E on the harness the fan also started. i dont want to install a switch but i am out of ideas. could it be the ECM? or a faulty conection to it? i would check it but i dont know where it is. PLEASE HELP!!
Race Director
Joined: Oct 2005
Posts: 11,770
Likes: 175
From: Rolla Missouri
2021 C4 of the Year - Unmodified Finalist
St. Jude Donor '10 thru '25
At what temperature are you looking at as overheating?
I only ask because a lot of new Corvette owners find it hard to believe the factory "fan on" settings for these cars.
I am not sure of the exact temp. for your year, but it will be over 215 F.
Most don't like that, but for a properly operating cooling system, that is not too hot.
Now, if you already know the specs that is should operate at, and it's just not doing it that is a different story.
So, I guess a little more detailed description from you would help. Then someone with your year C4 can probably help.
I only ask because a lot of new Corvette owners find it hard to believe the factory "fan on" settings for these cars.
I am not sure of the exact temp. for your year, but it will be over 215 F.
Most don't like that, but for a properly operating cooling system, that is not too hot.
Now, if you already know the specs that is should operate at, and it's just not doing it that is a different story.
So, I guess a little more detailed description from you would help. Then someone with your year C4 can probably help.
Racer
Joined: Sep 2008
Posts: 456
Likes: 0
From: FL
I was diagnosing nonexistent problem. Analog was showing high temp, but digital was OK and fans turned on OK.
Did your coolant boil? Keep in mind that if concentration of antifreeze is low it will boil before fans tun on.
Did your coolant boil? Keep in mind that if concentration of antifreeze is low it will boil before fans tun on.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
If you have a single fan only, it should come on about 228*. Since you have tested the fan and that relay it could be the ECM. If your digital coolant gauge is showing 240* with no fan, the only other thing that is easy to change is the coolant temp sensor but I would guess it is not that far off.
Thread Starter
6th Gear
Joined: Apr 2010
Posts: 6
Likes: 0
i am sure ive checked everything that is sposed to be checked. when i manually ground the ecm the fan starts with the relay connected. What would be the reason that my ecm is not grounding the relay at any temp and at any time when the car runs? that is the only option that i am left with i believe. the coolant temp sensor has been changed along with the fan relay. the wiring is fine since when i ground the ecm the relay is energized and the fan starts. also, the ecm has not stored any codes whatsoever!!!! any i deas anyone? it is soo frustrating. please help!
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Does the fan run when you turn on the air conditioning? The fan should come on when the a/c is on. Is there a possibility you changed the wrong temperature sensor? It sounds like the ECM doesn't know the engine is too hot. There are temp sensors in both heads. Are the connectors at both temp sensors good? Your relay and the fan are obviously okay.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Ecm should drive Main fan relay with 226 from the Coolant Temp Sensor or when the a/c pressure sensor opens at 228 psi. To see the former, you need a scanner and for the latter, a Manifold Gage Set. I'd guess your Display is bad (and if your Vette has the Aux Fan option and it's not coming on either, there's a good possibility that it is) or there's resistance in the Coolant Temp Sensor reference, or that Sensor is bad, or a bum ECM, but I'd rather see what the ECM is seeing first because it takes a lot of the guesswork out of it. You can check the Coolant Temp Reference (yellow) - should be 5 volts disconnected from the Sensor. You can simulate the a/c signal by disconnecting the switch (mounted on the high line next to the high limit) which should drive the fan. You can do a quick check of the Display by disconnecting the Temp Sender - right head between 6 & 8 - and with it open the Display should read Lo and then if you ground the reference, something around 300.
Thread Starter
6th Gear
Joined: Apr 2010
Posts: 6
Likes: 0
Finally! the temperature sensor was bought for a local auto parts store. for about $12. It resulted faulty after cheking the temp reading directly from the ecm. I went to a Chevy dealership and bought a sensor there for $90! Absolutley no more going cheap when it comes to parts! Thank you all for your input. it was very helpfull and appreciated.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Huh? The Coolant Temp Sensor - manifold - is about $12 at any Discounter and includes a new Pigtail; the Display Sender - right head - about the same at NAPA. Both are Thermistors and the engineering isn't rocket science with every car being made using them. Paying $90 would seem a bit steep. In fact I would have spent that on some sort of Scanner making it easier to diagnose the next time something goes wrong.