Expert: Rob Painter - 6/3/2011

Question
QUESTION: turn on AC fans come on.Unplug ETC sensor fans come on.Put jump wire in relay and fans come on.Tested the 3 relays all good.Put in new thermostat.Water pump works.Can not get fans to come on.Can not find Fan control module on 1988 caddy fleetwood.4.5 litre, FWD, not by hood latch on this car

ANSWER: Hello,

I wish I could help you, but I no longer have any manuals dating back past 5 years to tell you where this module is. You seem very knowledgeable in the diagnostics, but this engine is a real problem if its been over heated even once, just a little bit!

I have constantly written about the junk aluminum engine Cadillac used from 1982 to present. The minute these engine get to 220 degrees f, they are self destructing and it really doesn't matter anymore if the fans are circulating.

You did not tell me if you did a cooling system pressure check. If not pressurized because of even the smallest of leaks, the fans won't come on because the system is not circulating.

The aluminum engine is great for mileage and performance, but this problem is so rampant that you won't find an engine in a junkyard that is any good either. Cadillac was selling crate engines for $4k a piece and they made 10s of billions over the years on engines and parts.

These engines are notorious for cracked blocks and blown head gaskets which were not the cause, but the affect of overheating.
I write on this an average of once a week. In my opinion, if this didn't breed a class action, nothing did, but its too late now. GM released all their liabilities by going bankrupt!

When ever there is an over heating situation, the first thing done is a thermostat, then next a water pump. The water jackets are very small in this engine (4.1, 4.5, 4.9, 4.6) that a small part of gasket material left behind will plug it up and cause it to overheat. I have owned 20 Cadillacs over the years and loved these engines, but I was well aware of these issues to and if I were to buy one, would road test on a hot day to make sure there were not issues.

You might call around to local libraries to see if one has a factory manual for your car to find out the location of the module if in fact there was one used in 88.

I would definitely consider using a pressure tester on the cap and on the system to see if coolant is even circulating for the sensor to even pick up the engine is running hot.

Had a guy a couple weeks ago with a blown head gasket wanting to hard wire in the fan and I explained to him no point because even if you could cool down the radiator, the engine would not cool and would melt because the colder coolant in the radiator was not going into the engine due to no pressure in the system. You need 15 pounds continual pressure for the system to operate correctly.

In the next couple weeks, just to illustrate my point, I am going to have a fire or maybe I will just use charcoal without flames an put an aluminum can melting in seconds to illustrate what happens to an aluminum engine when exposed to heat.

At least with the cheapy AMC/Renualt Alliance, when they over heated, instead of replacing engines, one could purchase a piston liner kit and be back on the road in no time for a lot less expense than these Cadillac engines. Yes, GM really scammed the consumer and should have been required to have a big orange label on the dash with a warning--NEVER overheat this engine or catastrophic engine failure will develop immediately!

Good Luck!

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---------- FOLLOW-UP ----------

QUESTION: Just to let you know ,I replaced the water pump like 7 years ago and it leaked when i did.I was not going to do all that work again to put a new gasket on.So i tightened the pump up some more and threw some stop leak in it and let it leak for like a month before it finally closed up.System worked fine,leak finally stopped.No problems for like 80,000 miles.Pressure should have no bearing on a water pump,it runs all the time.overheated system many times before and it still worked,Thanks any way though it seems to be a mystery where the fan control module is (you can buy one but no one nows where it is located)Willing to pay money if you know of a someone who knows more about BCM and FCM.Went to local caddy dealer and they could not find it in the book.

Answer
Hello,

You are right. Pressure has no bearing on water pump. Sort of. Pressure controls circulation of the coolant. If the system is not circulating which is required in a closed system which you have which requires 15 pounds and the water pump is leaking, your system is not circulating. Thus overheating issues. This can explain why the fans are not coming on and not because of a module that you can't find.
I get the impression that you are attempting to argue with me about the dangers of over heating to this engine and it very well make the difference with your fans working properly and then you tell me you put stop leak in on top of it, which gunks up the coolant sensor in the engine.

Then you tell me you have been driving for years with no problems. All I can say is you have problems. The fans are not running. Who knows what damage you have done to this engine you are not aware of yet!

I don't understand how this engine keeps going with continual over heating, but numerous people are not that lucky!

It is possible that this car did not come equipped with the module you are looking for. If the Cadillac dealer couldn't find it and they probably have the component information on the car, how can I help you?

It's not a question of money. I would give you the answers you need for free if I had them. The car is 23 years old and I surely don't have reference going back that far.

If you can find someone with manuals, that may help. You can try Ebay to see if you can find the manual.

Chances are you have other problems with that engine like blown head gaskets and the stop leak plugged the leak as well as the cooling jackets between the heads and block.

When you originally asked the question I sure didn't think you would brag about running with a leaking water pump, over heating the engine and throwing stop leak in it! This is an aluminum engine in which components literally melt from over heating.


I have been dealing with these issues since 1982.

Good Luck!

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