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Coolant fan sensor location...


Gone but not forgotten
Jan 30, 2001
Hermosa Beach, CA
1987 Z51 Silver Coupe
Ok, why was it moved from one head to another?

I ask because of a discrepancy I found in Gordon's book. My GM Corvette service manual shows it on the left (driver's) head between #1 & #3 plugs, yet his book says that the 1984 sensor was in this location while the 1985-89 sensor is located between #6 & #8 plugs.

I know mine is original, but they obviously changed sometime between 1984 and 1987. My questions: When did they move it? and Why did they move it?
It's a matter of choice


What you need to remember is that there is really no difference between the LH head and the RH head, they are identical. The only change is that the sensor location between #1 & #3 on LH head changes to #6 & #8 on RH head. It's a choice of which head you're going to use. Obviously they changed from one head to the other at some point in time.

Now I'm confused,
Aparently Gordon made a mistake if he did say its on the drivers side in 84...its NOT...its on the passenger side..the OIL TEMP sensor is on the Drivers side....oh well even the "great ones" get it wrong occasionally!!
Aren't digital cameras cool?

Hey guys, since I can't seem to find accurate pictures of the various switches, relays, connections, etc., check these out: (click 'em to view full size)

What is the switch between #1 & #3 plugs, and what is the switch between #6 & #8 plugs? :confused

Oh, and while I'm at it, what is this box (cover?) found in the left front well area? The toggle switch you see is for my hood lights. ;)

picture#1 (top one) is your Fan Temp sensor.......

picture#2 (middle one) is your Engine Oil Temp Sensor..........

(on the 84 both of these are reversed)

Picture #3 (bottom) is the Hedlight Relay Cover...there are 3 relays under it that control your main headlights.......

If U were to upgrade the system to the later design(MUCH quieter and reliable)......the 3 relays were replaced by 1 relay/computer unit

The replacement is involved to say the least....I have the instructions posted at our website......its a multipaged manual!

PS YUP.............Digital Cameras Rule!!!

Thanks _ _ _ _ ?? I believe though, that the oil temp sensor is located at the oil filter/oil cooler location on mine. I remember having to fix that wire when I first got it. Is the switch on the right head the knock sensor? :confused

C'mon now, tell me; who does the typing? I know both of you do the WORK! :L

BroKen :Silly
Does anyone have a suggestion on how to remove the plug that is located originally between the cylinders 1 and 3 in a 91 L98 to replace an extra Fan switch sensor?
I have tried hammering it, rust removal, etc. I can't get it out! and the 5/16 square is getting round!
Any suggestion is appreciated
Geez, it really sounds like the sensor is seized in its threads. Someone didn't use teflon tape when they installed it. ;)

You have to be careful with aluminum too, don't be twisting it too hard until you get some lubrication in there somehow. There are several "rust busters" out there on the market, but I can't for the life of me think of one at this very moment.
Ken, the sensor between 1 & 3 is supposed to be for the secondary fan - at least for a Z51 setup. My 86 has no sensor in the left head; the main coolant temp sensor is at the front of the manifold.
Sorry for the three in a row. The knock sensor is on the block itself, just above the starter. The oil temp sensor is, as mentioned, between cyls 6 & 8.
Hey Rich, take a look at the date on this thread; it's an old thread. I just responded because Alvaro had asked a question in here instead of starting a new thread. Since 2001, I have learned a few things about the L-98 that I didn't know when I first posted this. ;)
Oh sugar! Sorry 'bout that, chief! I think the thread pre-dates my entry onto the CAC, which is why I didn't recognise it.
Ken / rubel:

Thank You very much for your responses.

Well, the 91 originally does not have a sensor in the hole between cylinders 1 & 3, it comes with a plug.

I am trying to add a sensor there to switch the fans on at lower temp, (Just like mid america suggest), but I cannot get the plug out.

Do you know if in the market exists a tool that is like an Allen wrench type but square, not hexagonal that is 5/16 seize?

Again. Thank you very much

Sounds like a square driver to me... There are a couple plugs on my car that require them (ex: some of the EGR blockoff plugs on the new manifold). I've got a set of small square drive bits I got from Black and Decker (a tool manufacturer) but I don't believe i have one that large. You might want to check out sears.com and look in the Craftsman tool section - they have almost anything you want. Alternately, Fastenal (should be www.fastenal.com) ships international and if they DON'T have it you can't GET it.
I will check at Sears here locally, thank you very much.
Do You think that the best way to take it out will be using rust remover or adding heat to the zone to release the pressure?
This seems unveliable tighten.
Heat may help you some, if you can get in there. I checked with my mechanic today and he said that basically, the correct tool is the only requirement. He did say that "rust buster" type solvents aren't going to do much good; it won't penetrate the threads far enough in the aluminum head.

Good luck and let us know how it works out.
I will try this weekend, and will let You know.

Again, thank so much.
to clarify

The '84 and early '85 used two coolant temperature sensors. The sensor in the pax side grounds the fan relay, activating the ONE fan; the LH side feeds the dash display and ECM. Later C-4s had two fans and a different setup. The oil temperature sensor IS near the filter.

Later cars had faster, more capable ECMs and Chevy used this computing power, eliminating, in this case, the second sensor.

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