Fan / Overheating problem... 94 Grand Prix

Hey guys,

I have been everywhere and have done everything to fix my problem.....maybe one of you can help solve this 2 year problem?

While driving my 1994 Pontiac Grand Prix SE 3.1L the temperature is fine. During the winter while driving or sitting the temperature is fine (due to colder outside)....in the summer if i stop at a light or in a drive thru or god help me, a traffic jam......my Grand Prix overheats. The fans will not turn on. They do work just fine for heat/air!

What i have done:

Jumpered fans to make sure both work......OK
Switched Relays to make sure both relays worked when i turned AC or Heat on......OK
Checked ALL fuses.....OK
Replaced Thermostat....Didnt help
Replaced Heat Sensor......Didnt help

Now after another frustrating day of replacing parts i turn to you guys.....any ideas??

Any info will help.....this is just driving me crazy!!

Todd

When you say it overheats does the overflow jug bubble or just the temp guage read high? If it don't bubble than its not overheating. A possible problem would be a skewed sensor reading wrong. Or just in warmer temps it runs hotter.

Possible overheating problems are a weak water pump, low on coolant, coolant leaks, a bad rad cap not holding pressure.

Originally posted by Flatrater
When you say it overheats does the overflow jug bubble or just the temp guage read high? If it don't bubble than its not overheating. A possible problem would be a skewed sensor reading wrong. Or just in warmer temps it runs hotter.

Possible overheating problems are a weak water pump, low on coolant, coolant leaks, a bad rad cap not holding pressure.

Hey,

First of all, thanks for the reply....believe me, all help is welcome!!

When i say overheat....i am saying that the temperature gauge reads near the red (almost 260) and the car starts to shake funny......once i turn on the heat to pull some heat from the engine, the car runs normal and temperature drops.

Basically i need to know what the heck is keeping the drivers side fan from turning on. I know it works...ive seen it work, but something is not telling it to turn on!

Thanks again.....anymore insight would be helpful!!

Todd

I have the same problem although I haven't changed the coolant temperature sensor yet. The one thing that will help is to run the air conditioner at all times, especially when the ambient temperature is above 40 degrees F or after going up a long hill. This will keep the other fan running.

Hello fellow 1994 Pontiac Gran Prix SE owners,

I also have the overheating problem as described for several years now. I got the car in 2008 and put a radiator and a water pump in it. Five years later I was losing coolant and found a crack in a plastic header of my "new" radiator so replaced it again. Now it is 2018. In the middle of winter of 2017 I developed a pin hole leak in one of the tubes on that replacement radiator and by spring it was shooting coolant all the way back to the firewall and all over my belt and pulleys.

I just replaced the radiator again and I have discovered the water pump is leaking. I couldn't tell until the spraying from the pin hole leak was fixed. I was told that I need to replace the heater core by a guy at a radiator shop. He said I had restricted flow through the heater core and that was causing my overheating problem. I have no leak inside my car and I don't smell antifreeze so I don't "have" to replace it because it is working. I still have heat in my car. I can't see any leak inside or in the hoses to and from the heater core. I was told by my brother in law that only about 5% of the fluid goes through the heater core anyway so it really can't be the problem (good for me because that looked really hard to do!).

The temperature gauge just reads higher than it used to but I have never had steam come out of under the hood. Do these gauges start to read differently as the car ages? One of my fans won't come on either even though I have replaced the relays. In summer it goes high on the gauge (about 230) at a stop light and then goes back down as soon as I get going again. I have 227K on it. Does an older engine just naturally run hotter. It "seems" like it is running hotter than it used to.

My main concern is a possible head gasket leak. My oil looks like regular oil. Brownish dark clear fluid. I have no gunk on my oil stick. No gunk (tan blobs) under my oil cap. The bubbles in my overflow tank have stopped now that I have replaced that radiator. I'm replacing the water pump tomorrow. I have not replaced the temperature sensor near the thermostat. I forgot to mention that I replaced the thermostat when I replaced this last radiator. I have the usual amount of condensation vapor coming out of the tailpipe at start up and cold mornings. I don't smell antifreeze in the exhaust. The coolant just doesn't seem to be coming out the tailpipe.

I just wanted to see if anyone else is having these same problems and see what they have tried that I haven't tried. Sorry for the long story. Any suggestions? I'm hoping replacing the water pump will fix it but I don't know if it will.

Well, anytime you have a leak, you are allowing air into the system....the air can create an air bubble or pocket, and this can block coolant flow, which will cause the vehicle to overheat.....

If you are getting good heat out of the heater core, it is not blocked....

What you have to do is stop the leak, wherever it may be.......and then refill with coolant, and properly birp the system to rid the system of air.......a great tool for this is the Lisle Coolant funnel setup....it allows you to fill and birp your system at the same time.....

Since your W/P is leaking, it should be replaced.......also now would be the time to replace the coolant in the system and also replace your thermostat....

Is this a 3.1/3.4/3.8?

Thank you so much for replying to my story so soon. It is a 3.1L. I just replaced the water pump today and I am letting the gasketing goo cure for the 24 hours it said before I refill my cooling system. I have just put in a thermostat last Wednesday when I put in the new radiator. Yes, the huge bubbles I was having in my coolant overflow tank have stopped along with the leak out of the radiator, yeah! When I refill my system I just fill it and keep topping it off with the bleeder valves open. I wait about 2 minutes between each topping off until it doesn't drain down anymore. I leave the radiator cap off and start the car. I keep filling it as it goes down and once the bubbles are out of the bleeder near the water pump I close that and put the radiator cap back on (usually just a few minutes). I have plenty of coolant in my coolant overflow tank too. I let it get up to temperature and the the bleeder near the thermostat starts bubbling for a while and I just let it run at idle for half hour with the bleeder screw just bubbling at the almost turned shut level. Does that sound about right? I almost forgot to say I have the heater on at full blast also. I hope I am purging the air. I ran the engine for 20 miles with just the new radiator and thermostat but it was still "overheating" in that the temperature gauge kept looking like it was near 230 and the low coolant light would stay on. It took me 4 hours to go 11 miles to get to a radiator shop. I kept pulling over and letting it cool down to 100 before I would start the car to go a little further. He found the water pump leak. He told me to leave the heat on to trick the fan to stay on and I was able to drive it home and the gauge stayed right at the 210 mark. I never had steam coming out of the radiator cap, just the low coolant light turning on and off and the temperature gauge beyond 210 but not at 260. In your opinion would you investigate a possible head gasket leak with a pressure test? I think I've got the major leaks fixed but I still wonder if coolant is still going somewhere else. I did do the hydrocarbon sniff test 2 years ago and there was no color change. Which test do you think would work the best at checking for a head gasket leak. The car is at 227K now.

You are kind of between a rock and a hard place.......

We are talking about a 24 year old car.......
There comes a point where you have to make a decision to stop putting money into a vehicle and investing in a newer one.......

3.1's are known for lower intake leaks.....let them go too long, and you create problems like head gaskets......

Wish I had crystal ball to tell you how long your car will last, or what future problems you may have, like rusting brake and fuel lines, transmission problems, engine problems, etc., but I don't....

I was hoping you could let me know if the air bleeding procedure I do is good enough since the manual says "Caution: this car has a specific coolant filling procedure." I'm not flushing the system or adding any special chemicals or "sealants" to my system or pulling the block plugs like it tells me to. I know it is an old car, I'm just going to refill it.

My husband bought a brand new car (2008) and it had major transmission work in just two years and he is good with his cars. In the ten years he has had it he has had $1000s of dollars of work done (by dealer and others) on it including a head gasket, bearings; both wheel and transmission, and the drive shaft hanger bearing still needs to be replaced and the part is $1000 (the drive shafts are all one part now). Besides all the maintenance of timing belt etc. It is a crap shoot with any car, new or old. I am doing the work myself so that does bring the cost down! It has no rust. The underside still looks new. It is a west coast car. People at the car parts shop don't think it is a "wreck". It was well taken care of to last this long.

My other car is a 1979 Chevy Malibu that needs a lot more work and the body went bad when it got here. It does have a new engine though. I do understand that most people don't want to work on an old car cause they figure it is all rusted up.

I am a stay at home mom that doesn't have to go anywhere when they put the chemicals down in the winter. It is not all rusted up. I did the brakes myself and everything came apart fairly easily. Nothing broke trying to get the brakes repaired. I took the calipers off and everything apart and got all the pins to slide really well. Some of them had gone dry. Used the "Silence is Golden" grease on the pins and put new boots if there was a crack. At least brakes are pretty easy to bleed but you need 2 people. They have worked very well since I did them. I was down to the shoe plate on 2 of them but not to the caliper pistons.

So new brakes, exhaust is good, body is good, a couple reasons to try to keep it going. I don't want someone to tell me it is not a head gasket. I just want someone to tell how to find out if it is or is not the head gasket. I did the sniffer test on it 2 years and 10,000 miles ago and it didn't change color. Since I replaced the radiator and the thermostat, each time when I started it, no coolant came shooting out the the uncapped radiator neck. I did the filling procedure 3 times but I had only gone 20 miles with it. Now I have a new water pump on it because that was leaking. What are the best tests to find out if it has a head gasket leak? I just need the expertise that I do not have to find the answer yes or no. Then I can make a decision. I don't feel like throwing the car away yet. I need that answer. I wanted a pressure test at the radiator shop and he didn't do one for me. I thought that would help but I did have a water pump leak. Should I go back now and ask him again for a pressure test now that the new water pump is on? Is there a danger to do that to an old car? Should he be reluctant to give me the pressure test? Will it give me my answer? I know if the pressure falls there is still a leak somewhere. Are these leaks sometimes hidden inside? I know the head gasket can leak in all kinds of directions. You mentioned a cracked cylinder head. That is the top of the engine right? Maybe you could explain if that would be hard to diagnose. Any info would be appreciated. Thanks for your input so far. I thought I should explain why I am still trying to keep the car going. I do have boys, a 12 and 13 year old that I am expecting will need their mom to run them around soon.

In essence, you perform a pressure test every time the engine warms up. However, doing that with a cold engine can reveal problems that won't be quite as apparent with a hot engine.
If the cooling system builds pressure when the engine gets up to operating temperature, that is a good sign that there are no major leaks.

As for bleeding air from the system, there is a bleeder screw in the coolant crossover pipe on the front of the engine, almost directly over the water pump.
There is another bleeder on the thermostat housing. These bleeder screws can be loosened when the system is pressurized to expel air.

http://www.wwdsltd.com/files/191V-6CoolantAirBleeders.jpg

T-2 is correct. These engines have a tendency to suffer from lower intake manifold gasket failures. Not all of them do it, but it is not uncommon.

Repair involves draining the cooling system, removal of the upper intake (plenum) and throttle body, removal of the rocker arm covers and lower intake manifold,
removal of the old gaskets and seals, repair of any erosion or pitting of the aluminum, and replacement with new (upgraded) gaskets.
Very often there will be erosion of the head and lower intake surfaces around the coolant openings.

http://www.wwdsltd.com/files/191CIDIntakeFlangeErosion.jpg


This damage must be cleaned and repaired, usually by filling with metal-bearing epoxy.
This is a time-consuming repair, partly due to the required cure time for the epoxy before scraping it flat before assembly.

http://www.wwdsltd.com/files/191CIDHeadFlangeFinished.jpg


The mating surfaces if the lower intake manifold should be treated the same.

Regarding the secondary cooling fan, the factory programming usually will not operate the secondary fan until the coolant temperature is well above 230°F. My hacking of the binaries for factory programming most often reveal this parameter is closer to 113°C (236°F). Incidentally, these fans are also shut off when road speed is above 41 MPH unless coolant is above 236°.

This secondary cooling fan will also operate if the A/C is operating and the evaporator pressure is above 25 PSI to assist with refrigerant condensing. This fan will also operate if the PCM is in a backup fuel mode, as occurs when an error code is set or when the system is in diagnostic mode when a scanner is connected.

If the secondary fan operates in any of these modes, it is obviously not a problem with the relay or control system. It is possible that the coolant temperature sensor is reporting an incorrect value, but a scan of the PCM would reveal whether the reported temperature is reasonably close to the measured value. Since your instrument panel displays the temperature with some variation, we can presume the coolant temperature sensor is not completely dead.

Thank you gentlemen for answering my question! The pictures look just like my car! Thank you very much. I had posted how I was doing the filling procedure. Thanks for the advice that starting it does a lot of that for me. I have used the bleeder screws. Thanks for showing them in the picture. So you are saying that if a pressure test is done, it could indicate a chronic problem with the engine that won't be visible. I have replaced a timing chain (sprocket went bad) on my old Malibu before I got the newer engine in it with the roller push rods since my old engine had the cams go flat. If I'm still having this problem I may tear into it to get "my car back". I've played with cars since I was 15 but I'm NO expert. Thanks for telling me that the fans may be working okay. I have seen that second fan come on in the summer when I was running the air conditioning (still works). I have the time but no money. Isn't that how it always goes?

Update: With the new water pump (and radiator and thermostat) my car only went up to the 210 mark when I was idling at a stop light. Generally it stayed at 4/5ths of the range on the temperature range from 100 to the 210 mark. That is definitely an improvement. It used to run at about 3/4ths of the range before this last radiator leaked. I will still try to see if I can bleed more air out of it. The upper radiator hose is always more "stiff" (goes to the thermostat) than the other hose going to the radiator inlet on the water pump side. Is this normal? My brother in law says it is. I just thought I would ask this forum too. The guy at the radiator shop said it was too stiff so I had an almost blocked heater core. I did not do anything to my heater core. So, if it is the lower manifold, what symptoms should I be looking for? It was in the 70s and very humid when I ran the car yesterday. I have not tried the air conditioning because I was trying to get a sense of how it is operating now compared to when the radiator leaked. When I turned off the car the gauge went to about 230 and I never saw the fan come on. I'm not sure I ever paid attention to the temperature gauge after I turned the car off. I'm not sure that this is normal. It probably is. By the way, both of the hoses "feel" the same flexibility when they are detached from the radiator. It is a relief to have no visible leaks! Thanks again for your input. If I have this lower manifold problem, I would much prefer to fix it this summer rather than in winter where I have no warm garage. Are there any "markers" or anything I can put around the coolant system to check for this lower manifold leak? (Just an aside, I lost one of my bleeder screws when I was bleeding the system. Don't ya just hate that! I opened it up too far and it "rattled" and got pushed out by the coolant; huge fountain since car was running. Luckily I was downtown and could walk to an auto parts store to get another one.) I have been trying to figure out how to "thank" you people on the website but I haven't figured it out so thank you blue bowtie!

I love to use the Lisle Funnel, that attaches to the radiator fill, for birping....

Another thing you can do is this........jack up the front end......Blue's picture with the arrow pointing at the bleeder, just above the end of the arrow is a rubber hose....slide the clip off on the right side.....with radiator full to the top, stick a pick or small screwdriver between the top of the hose and the metal pipe.....this creates a small opening for air to escape.....when coolant starts to really flow(have a rag underneath), remove pick/screwdriver......if coolant level dropped in radiator top off......repeat......install clip on hose...install rad cap and lower....

Hi Tech II,

Can I burp out of the radiator outlet? The inlet to the radiator is low on the radiator on the water pump side so I think I would lose a lot of coolant. The outlet has the higher hose but I would worry about sucking in air? I have bled the system a couple more times using the bleeder screws. It has not had the temperature gauge go past the 210 mark now for a couple of runs around town. Today is the big test of about 45 minutes at highway speeds. Thanks for the suggestion. If I have a major temperature rise again I'll see if your suggestion will help.

Well, after all the "burping" you have done, all I would do, is take the radiator cap off first thing in the morning, top off the radiator, put cap on, and go run it.......then see if the temp gage is ok....

Hi again Tech II, Will do! Thanks.

Have you replaced the rad cap? It's cheap..

Hi Again, I replaced it a couple of years ago but not recently so I will try that also. Thanks for reminding me that it may be a culprit in addition to all that I have replaced recently. It turns out my long trip got cancelled the other day so tomorrow morning I have to go an hour away at highway speeds. I have topped off the radiator again. I hardly had to add any coolant. The radiator cap seems to be keeping pressure. It is very hard to remove if the coolant isn't cooled all the way down. That's why I had to wait to let it cool down to fill it up again before I replaced the water pump. Thanks again.

Hi Again, Update on first hour long highway trip to and from. The car stayed about 4/5ths of the way between 100 and 210 on the temperature gauge all the way there. I had to stop at a couple of stoplights and it climbed to 210 but would go down as soon as I started moving again. I have not replaced the radiator cap yet. It had an hour to cool down. So I started back home. About 10 miles go by and the low coolant light comes on so I get off the highway. As soon as I park in a level spot the low coolant light goes out. I turn off the car anyway. Look in the engine area and I can't see any drips. The overflow is full up. I decide to burp at the thermostat again so I start it up and loosen the bleeder and just coolant shoots out, no sign of trapped air. It is hot so the thermostat is open right? So I start home again. Right when I get to a big bridge the low coolant light comes on again and I'm only another 5 miles along, still reads at 4/5ths of T gauge. Before I get off the bridge the light goes out and the temperature gauge jumps down to halfway between 100 and 210! I haven't seen it that low in forever. But it climbs back up to 4/5ths again. I've let it cool at home. I'll check the level in the morning when it is really cooled down. It runs very smooth, the bubbles in the overflow tank are gone now. Do I still need to put in more coolant a few more times? Could it still be some air bubbles trapped somewhere? I have left my heat at full blast all through this to help with the cooling. Any ideas or am I just being too worried about the temperature now? I just don't want to lose another radiator again. That will be the fourth one in 10 years.