Erratic Overheating/Electrical nightmare

[Limoguy]

1992 Brougham, stretched to limo with second heater and AC in the back. 62k miles.

The engine will occasionally overheat. The coolant reservoir will in these cases be full of boiling fluid. But here's the fun part. When the air conditioning IS FUNCTIONING PROPERLY, the coolant fluid will circulate and the engine will NOT overheat. However, if the A/C is on but the compressor stubbornly will not cycle, the the engine overheats as described above. I can even turn the AC off and do fine, as long as the AC WOULD work when turned on.

When does the AC not function properly? Well, it depends a lot upon apparent random chance, but also upon where and how you touch the stupid electronic control panel in the dash. I swear I am not making this up. The AC can be screwing up, but then I can push the upper left hand corner of the panel, and the AC cycles and the coolant fluid starts to circulate and all is well. So in the summer I just check to see if the AC works before pulling out of the driveway. But in the winter I can't tell if the air is blowing cold fro AC or from ambient temp.

But lately my little corner-of-the-panel thing just isn't working anymore. SO now I've got this weird collaboration between the electronic panel, the coolant circulation, the heater and the AC, all working together to strand me and my 5 kids on the side of the road with an overheating limo at the most inconvenient times. It took me almost 2 years of frustrating experiences to nail down the correlation between these issues.

It's NOT the thermostat. It's NOT the water pump. My buddy suspects vacuum pressure issues.

Any help here?

[Texas Jim]

Does the car have "ELECTRIC" fans...or does it have the old style "CLUTCH" fan?

[Limoguy]

Does the car have "ELECTRIC" fans...or does it have the old style "CLUTCH" fan?

Here's what I see: One fan, apparently the main radiator fan, is located aft of the radiator, in front of the engine block. It turns on the same axis as the water pump, is turned by the serpentine belt, and with engine off the fan blades can be spun free by hand, though the serpentine belt doesn't move. I assumed that this was a clutched fan.

However, there is also a smaller fan forward of the radiator, covering only part of one side of the radiator, which is an electric fan.

[Texas Jim]

Does the car have "ELECTRIC" fans...or does it have the old style "CLUTCH" fan?

Here's what I see: One fan, apparently the main radiator fan, is located aft of the radiator, in front of the engine block. It turns on the same axis as the water pump, is turned by the serpentine belt, and with engine off the fan blades can be spun free by hand, though the serpentine belt doesn't move. I assumed that this was a clutched fan.

However, there is also a smaller fan forward of the radiator, covering only part of one side of the radiator, which is an electric fan.

OK..thats what I "THOUGHT" it had...wasn't sure.

It looks like it is a combination of TWO things.

The clutch fan is possibly bad, and thus not pulling sufficient air thru the radiator.

The ELECTRIC fan only works when the ac is ON, so therefore, when the AC does not come on... neither does the electric fan.

With the electric fan not coming on, and possibly a bad clutch of the engine driven fan... equals not enough airflow thru the radiator and thus leading to overheating.

[Limoguy]

Does the car have "ELECTRIC" fans...or does it have the old style "CLUTCH" fan?

Here's what I see: One fan, apparently the main radiator fan, is located aft of the radiator, in front of the engine block. It turns on the same axis as the water pump, is turned by the serpentine belt, and with engine off the fan blades can be spun free by hand, though the serpentine belt doesn't move. I assumed that this was a clutched fan.

However, there is also a smaller fan forward of the radiator, covering only part of one side of the radiator, which is an electric fan.

OK..thats what I "THOUGHT" it had...wasn't sure.

It looks like it is a combination of TWO things.

The clutch fan is possibly bad, and thus not pulling sufficient air thru the radiator.

The ELECTRIC fan only works when the ac is ON, so therefore, when the AC does not come on... neither does the electric fan.

With the electric fan not coming on, and possibly a bad clutch of the engine driven fan... equals not enough airflow thru the radiator and thus leading to overheating.

Thanks for the reply. But here's why that doesn't seem to be it: First, your answer doesn't explain why the coolant fluid boils in the reservoir and does not circulate when the AC is malfunctioning, and does circulate and cool the engine when the AC is functioning properly. It's not just engine heat that's the problem -- it's coolant fluid non-circulation that is leading to the overheating.

And second, the AC doesn't actually have to be ON and BLOWING in order for the fluid to circulate properly; no, it only has to be in a state that it WOULD work if I turned it on. Which is why what I used to do every day before I drove it was to check to see if the AC would blow cold and the compressor would cycle. If it did, I would turn the AC off (it wasn't that hot a day) and I'd drive the limo with no problems. But if the AC did NOT blow cold and the compressor would NOT cycle, then I'd have to do a rain dance, sacrifice a young virgin pig without blemish, turn the car off and back on, and push the corner of the instrument panel, and test the air again, over and over, until by some cosmic error it blew cold. THEN, if it did blow cold, I could pull out of the driveway and be fine.

[Texas Jim]

I assume it has the 5.7 litre engine.

If the water pump is working...the coolant "IS" circulating.

I am also assuming that ...as you stated...the thermostat and the water pump is OK.

First....If there is NOT sufficient airflow thru the radiator, it WILL get hot.

When it gets hot, it WILL boil back thru the overflow tank.

I may be way off base, but I think it all boils down to, not enough airflow thru the radiator at low speed.

(Pun intended)

You didn't say...bit I am guessing that if you run at 50 mph or so...it never overheats till you slow down.

THEN it gets hot.

I feel, at this point, that the clutch fan is bad. (fairly common)

And if it "IS" bad...and the AC isn't working, therefore turning on the electric fan...at low speed, there is almost NO AIR coming thru the radiator.

I will venture to say, that if you either replaced the clutch fan, or had some way to turn on the electric fan "MANUALLY", whenever you wanted it on, you would have "NO" overheating problems.

Unless there is something internally wrong with the engine...like a blown head gasket...but then it would tun hot ALL THE TIME...no matter what fans were or were not running.

Maybe someone else can jump in here with more ideas.

[WinoBot_Beta]

Limoguy, you mentioned that you had to push in on the climate control panel sometimes and temperature had an affect on the problem.

My 86' Deville was notorious for electrical accessories not working due to the connections not making proper contact although you'd swear they were all the way in and tight. It got pretty frustrating to have to get out of the car in -30 degree Celsius to get my blower motor to work or when my digital dash decided to flicker and cut out spontaneously in cold weather.

I'd check the connection on the back of the climate control and see if it is corroded, loose, or just not making proper contact. There were times when I had to get a small bladed screwdriver and slightly bend the electrical contacts so they would touch again. If the climate control module is malfunctioning and a couple connections may not be making good contact to start the AC compressor and fan, then that may be one problem. The clutch fan sounds like it is toast however and not an uncommon thing to go as Texas Jim said, and especially on a 17 year old car.

Either way though, it wouldn't hurt to investigate the climate control module. They can have a tendency to get fussy and only work properly 50% of the time from what I've read.

[Limoguy]

I assume it has the 5.7 litre engine.

If the water pump is working...the coolant "IS" circulating.

I am also assuming that ...as you stated...the thermostat and the water pump is OK.

First....If there is NOT sufficient airflow thru the radiator, it WILL get hot.

When it gets hot, it WILL boil back thru the overflow tank.

I may be way off base, but I think it all boils down to, not enough airflow thru the radiator at low speed.

(Pun intended)

You didn't say...bit I am guessing that if you run at 50 mph or so...it never overheats till you slow down.

THEN it gets hot.

I feel, at this point, that the clutch fan is bad. (fairly common)

And if it "IS" bad...and the AC isn't working, therefore turning on the electric fan...at low speed, there is almost NO AIR coming thru the radiator.

I will venture to say, that if you either replaced the clutch fan, or had some way to turn on the electric fan "MANUALLY", whenever you wanted it on, you would have "NO" overheating problems.

Unless there is something internally wrong with the engine...like a blown head gasket...but then it would tun hot ALL THE TIME...no matter what fans were or were not running.

Maybe someone else can jump in here with more ideas.

The fan works fine. The engine will overheat on the interstate at sustained speeds over 60 mph. And, don't forget, the engine will do fine when the AC is turned off completely, as long as it is in a state where it WOULD blow cold if I turned it on. So this problem has nothing to do with the fans, and nothing to do with the radiator itself.

To say water pump functionality necessitates proper fluid circulation is not correct. One example is a bad thermostat. My thermostat is good, but that's just one example of how there could be an impediment to circulation even with a functioning water pump. My water pump and thermostat are both good (replaced, and even the old ones were fine).

What I'm dealing with here is either an electrical or vacuum problem that screws with the circulation of the coolant fluid, perhaps by diverting/rerouting the fluid erroneously. I need input from somebody who has experienced this kind of problem, or who knows the intimate details of a 92 caddy coolant circulation system.

WinoBot_Beta, I thought about that. I tried pulling out the panel and cleaning all the connections, but that didn't seem to help. Of course, I only cleaned the connections behind the control panel, and who knows where in that GM spaghetti wiring the problem might be. Ugh, this is frustrating. I've considered just ripping out most of the hoses and simplifying the entire coolant system and just going without heat. At least then I could drive the thing.

[WinoBot_Beta]

Is there a valve or anything on the coolant lines going to the back that may restrict flow of coolant to the rear heater?

[Limoguy]

Is there a valve or anything on the coolant lines going to the back that may restrict flow of coolant to the rear heater?

Well first of all, there are several pieces of hardware in the coolant lines that appear to be valves -- they have vacuum lines running to them, so I assume they are valves. It is not readily apparent whether these have anything to do with the rear HVAC unit. However, I'm not sure whether the rear unit has anything to do with the problem. (BTW, the electric fan I spoke of earlier -- the small one in front of the radiator -- has its own radiator/heat exchanger and appears to be the heat exchanger for the rear AC unit (there is a hose running from it back to the rear unit), for whatever that's worth.)

What are you thinking about these valves? Whether they control fluid that goes to the back or not, they certainly appear to involve the main. Did you have an idea here?

[WinoBot_Beta]

Is there a valve or anything on the coolant lines going to the back that may restrict flow of coolant to the rear heater?

Well first of all, there are several pieces of hardware in the coolant lines that appear to be valves -- they have vacuum lines running to them, so I assume they are valves. It is not readily apparent whether these have anything to do with the rear HVAC unit. However, I'm not sure whether the rear unit has anything to do with the problem. (BTW, the electric fan I spoke of earlier -- the small one in front of the radiator -- has its own radiator/heat exchanger and appears to be the heat exchanger for the rear AC unit (there is a hose running from it back to the rear unit), for whatever that's worth.)

What are you thinking about these valves? Whether they control fluid that goes to the back or not, they certainly appear to involve the main. Did you have an idea here?

Just was curious if they would close once the rear AC would be turned on. I'm not at all familiar with the rear climate control on these cars, but maybe to keep the heat from flowing in during AC operation, the vacuum lines may close off to the heater core in the back and possibly redirect the coolant to keep it flowing hot and fresh so that if and when the heat is requested, it will not take such a long time to get the core hot again. Otherwise if there were just valves at the core, the valves would stop it from flowing into the core but the coolant in the return and supply lines will just sit and cool off without circulation. Reheating those lines would take more time and there wouldn't be anything Cadillac about that, which is why there may be more control over the circulation in this car.

Maybe one or more of those several areas might be the culprit? Its hard to say but just my two bits.

Have you found any literature on this model?

[andreajones021]

But if the AC did NOT draft algid and the compressor would NOT cycle, afresh I'd accept to do a rain dance, cede a adolescent abstinent pig after blemish, about-face the car off and aback on, and advance the bend of the apparatus panel, and analysis the air again, over and over, until by some catholic absurdity it blew cold. THEN, if it did draft cold, I could cull out of the driveway and be fine.

_________________

Bathroom fan

[Cadillac Jim]

This sounds very much like a clogged bypass. The bypass allows circulation when the thermostat is closed. When the bypass isn't flowing, hot water will never reach the thermostat. If the heater core valve is on, that flow duplicates that of the bypass, so this accounts why things are OK when the HVAC is on, whether or not it is blowing cold air or whatever.

You should also check the electric fan to make sure that it runs when the A/C is on.

Fan clutches have limited lives. The thermally operated ones can have short lives and need to be replaced every year or so if the car is driven in clogged traffic a lot. The RPM driven ones have longer lives. My inclination when I drove cars with clutch-driven fans was to use the thermal clutch and change it when it quit working. My test was to downshift to low at 30-35 mph when I saw the temperature gauge move; if I could hear the radiator fan whir until the engine cool, then quiet down, the clutch was working. If it didn't speed up when I downshifted, I changed it.

Another alternative is to replace the fan clutch with a spacer, so the fan turns with the engine all the time. This may increase engine noise in certain circumstances and decrease highway fuel economy slightly, but I doubt that these are considerations with a stretch limo and you have a long-term zero-maintenance solution.