Hey everyone! I need some help with my overheating 85 Fiero GT. Any help or suggestions would be greatly appreciated.

Here’s the deal:
1 It will startup and idle fine, temp stays around 190F. (I have a 180 t-stat in it).
2 Fan works, heater blows warm air.
3 No visible coolant leaks, water pump turns fine.
4 No visible smoke/steam from exhaust.
5 Plugs are not “steam cleaned” from coolant in intake.
6 Compression is decent (lowest within 70% of highest).
7 No coolant in the oil or oil in the coolant
8 Overflow tank line not clogged, radiator is clean.
9 If I drive it, it stays cool (below 220)

But then out of nowhere after 25-30 minutes it starts to overheat. Rad fan and heater on full blast will not cool it back down. Also, the check engine light will come one about 20 minutes in. If I pull over and shut off, light stays off and doesn’t come back on.

Here are the questions:
1 could this be a faulty water pump? (plastic impeller slipping?)
2 perhaps I still have some air in the system? (tried to burp it the best I could)
3 could there be an internal motor leak that I am missing?
4 if the car gets hot enough to where the radiator cap pops, is this hot enough that the head gasket could crack/heads could warp? (isn’t the point of the 15psi cap to prevent this?)
5 what is the deal with my check engine light?

Thanks in advance for any help!!

1 Yes
2 Yes
3 Prob not
4Yes - The light is the point to prevent it. The cap won't open up at that point. Past that point is trouble. You can also have trouble before that point but unlikely.
5 Do this

http://www.youtube.com/user...g#p/u/67/sRoSMhEL3Ms

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Does the front radiator fan come on?
Have you checked for crushed pipes?
Have you back flushed your radiator?
How old is your radiator?

Welcome to the forum,yes your correct could be a impellor that came off or loose in the water pump.Do tou see any water dripping anywhere,expecialley around the water pump.If you have a major loss of power then your cats bad (probubley not that).Can you visibley see the radiator fan running?You might just pull the thirmistat, and reinsert it if you have any smog check.It will run a little richer.If the fan is running full speed then your engine light is functioning correctley.Check all your fluid levels oils,tranney,coolant.Only other thing I can think of would be the radiator,does your coolant have rust in it (clogged radiator)?You can test your thirmistat,by placeing it in boiling water and see if it pops open (probubley not that if its new).

[This message has been edited by James Bond 007 (edited 09-10-2010).]

Thank you guys for the quick replies!
I will definitely try the light test to see what the check engine is all about.

As for the cooling:
Phonedawgz,
1 The fan does come on via the temp switch…I know this because when it got hot during testing (just into the red), the fan was on with the AC off.
2 The steel pipes are not crushed and when I run a hose through the thermostat housing either down through the block or through the return hose it flows freely from the radiator drain
3 As for flushing, I have run a hose through the thermostat housing and used Prestone cooling flush. The flush removed some “dirty water”, maybe slight rust?
4 The radiator could be original, but it is clean on the outside.

James Bond 007,
1 when I run the car, before it gets hot…if I open the radiator cap I can see the pump drawing water back to the motor. The return hose is not collapsing, and as I stated, the heater does blow warm air so I assumed there was flow.
2 I will try the light test to get the engine code…could be a cat
3 I do see the fan running, and I do not see any dripping or external leaking
4 are you saying that the check engine light will come on if the fan is running full speed?
5 the thermostat is new and the radiator flows water freely (my water bill will testify to that!)
6 I will check all of the fluids this weekend

So my questions now are:
1 if the water pump impeller (maybe plastic) is slipping, would it only do it after 25 minutes of runner? Maybe it has to get pretty hot before it slips?
2 does the check engine light come on if the ran runs at “full speed”?
3 if I had a bad head gasket, cracked block, or warped heads, wouldn’t the car just overheat right away? (btw…it purrs like a kitten!)

Again, thank you both so much for your help…I love this little car and want so badly for it to be reliable!

Does the waterpump look like it has been replaced?

How much flow do you see at the thermostat housing?

You should back flush the radiator. The radiator tubes get stuffed with crud from the normal flow. You need to force the water to flow in reverse and have that water drain OUT not into the rest of the cooling system. Best way to do it would be remove the radiator. Inspect the tubes as much as you can when you have it out. Suspect the radiator long before the water pump.

Check enigne at full speed? Only if there is some other trouble

Warped/cracked heads causing overheating. The way a bad head/head gasket causes a car to overheat is the pressure inside the cylinder is much greater than the pressure in the coolant system. The leak at the head overpressurizes the coolant system and forces the coolant out of the cap, filling and then overflowing the reserve tank. The missing coolant then causes overheating. If you are not seeing this don't worry about leaking heads, untill you try the other fixes first.

Don't continue to run the car after the temp light is on. Let it cool down.

The front fan is controlled by a relay. Two different things can turn on the relay and thus the front fan.
One is turning the AC on. The relay is hotwired to come on anytime the AC is turned on. The second is the fan temp sensor switch on the engine. So the fact the fan came on with the AC on is cool, however that doesn't mean the engine temp switch is ok. If the fan comes on without the AC on then that means the temp switch is ok. The fan should come on before the overheat light comes on.

Turning on the heater to full/hot and the fan to high helps cool the engine. It also bakes the driver and passenger but yeah

84's have a two speed front fan. All others have only a on/off front fan. The SES light will come on if the ECM sees an overheat condition. Don't wait for that with the TEMP light on. Whichever comes on first is an indication you need to take action now. Since the SES light also comes on for other reasons the TEMP light is the one you will want to moniter first.

[This message has been edited by phonedawgz (edited 09-10-2010).]

Phonedawgz,
Thanks for the great info. I should clear a few things up:

1 I will check the water pump this weekend to see if it looks like a replacement or original. Do you know which had the plastic impeller? (oem or some aftermarkets?)

2 I believe if I open the thermostat housing while its running is will spray out of the housing. I haven’t ever tried that without the thermostat in, perhaps that’s where I’m getting air. (if there car is cold, the engine is running, and the t-stat cover is off, should it be spraying out, or flowing nicely?)

3 I think I cleaned the radiator well, but I can try again this weekend and use some more of that cleaner with a reversed flush (not into the motor…good point about flushing crud into the engine!)

4 what do you mean about checking the engine at full speed?

5 I did notice that after the motor overheated last night, the overflow tank had filled and overflowed a little bit! (hope this is not a sign of head damage )

6 I have yet to see the temp light come one, only the check engine light came on. Interestingly enough, if I just turn the car off and then back on the light stays off, even though the engine hasn’t cooled at all. This light seems to appear before the engine even gets above 220F. Maybe it is unrelated?

7 The fan comes on above 220 even if the AC is off


Tonight I will try to see if I have any air in the system. If this doesn’t work, I will check all of my fluids, try to check any trouble codes, clean the radiator (back flush).

Again, I am stuck on the 25-30 minute issue. Why doesn’t the car overheat right away? It gets up to operating temp in a few minutes, then runs perfectly for another 20, then overheats. Why does it take 20 minutes of running to overheat? Wouldn’t a bad head gasket/cracked head cause issues right away?

Are there any other tests I can do for the heads/gasket? Perhaps with the thermostat removed?

Thanks again!

Well for sure don't pull off the cap after the engine has gotten hot and pressurized. One trick is to squeeze one of the larger radiator hoses to see if there is pressure in the system. If there is hot antifreeze will spray all over you and your engine.

The thermostat cap comes off like a radiator cap - twist counter clockwise till it stops - push down and twist more. Do it while cold. Yeah try it with the thermostat out. That is not a final fix but its worth a try.

You should be able to pull the thermostat cover off and run the car. It sounds like you haven't done this to fill the engine with antifreeze. One problem you WILL have is as the engine warms up, air in the engine's coolant passages will expand and want to push antifreeze out the thermostat housing. When this occurs you can cap the housing and turn the radiator cap open but still in place to let the overflow go into the overflow tank. What you are looking to do is to get all the fluid moving, getting the air out and refilling at the thermostat housing. Close the radiator cap as soon as it seems you have relieved the pressure and then go back to watching the coolant move at the thermostat housing.

If you haven't done this, try it before the reverse flush. If you haven't properly burped the system of air that is MOST likely the cause of your trouble. See the top of this page for Ogre's cave and look up burping the system on his page.

Full speed - that was your question #2. I really didn't understand it

5 - coolant in the overflow tank - The level of the coolant in the overflow tank will go up, from the cold line where it shoudl be when the engine is cold, up to the HOT line when the engine is hot. This is normal. If the engine is overheated and the coolant boils, that will force the coolant to over fill the overflow tank and be lost. (Don't let this happen, take action when the light comes on) That however is not an indication of a head problem. Overflowing the resivour when not overheating the engine IS a sign of a head problem.

7 - fan comes on - Great - It is supposed to do this. That doesn't mean the car is overheating btw. The fan comes on before the engine is in an overheat condition.

6 - Yeah the check engine light coming on is most likely a totally different unrelated problem. Have you looked at the codes?

https://www.fiero.nl/forum/A...100421-2-096358.html

[This message has been edited by phonedawgz (edited 09-10-2010).]

Phonedawgz,
You have been a great help. I feel like the gears in my head are overheating now!

I will check the operation of the temp gauge and light tonight!

The “full speed” comment was in response to James Bond 007. It seemed as though he was saying the fan at “full speed would set of the check engine light”. I don’t think this is correct.

I will do what you suggested and see what the codes are tomorrow.

I must not have burped it properly. This is what I did:

1 fill the thermostat housing with the thermostat installed (the thermostat has a 1/16 hole in it to let the air bleed out)
2 after the radiator overflowed I capped it and continued to fill the thermostat housing
3 once air bubbles stopped coming out of the 1/16 hole I pulled the thermostat out and topped off the thermostat housing
4 this is where I had trouble…I couldn’t run the car with the thermostat cover off because it sprayed/poured out of the housing (even though the engine was hot). Instead, I elevated the front of the car and filled the radiator while it was running. I did this because the water pump seemed to be drawing the coolant back to the thermostat housing faster then the radiator was filling. (clarification - with the car off, the radiator would overflow, with the car running I could fit more coolant in)
5 I then ran the car and let it cool down a few times. Each time it cooled i checked the thermostat housing for air and found no air (coolant would flow out immediately-I assumed this meant the system was full)
6 I didn’t notice and temp needle jumping while idling (signifying hot air pockets passing the sensor) so I figured I was free of air pockets (stupid assumptions!)

Questions:

1 I drilled the 1/16hole in my 195 t-stat and used it for filling, after I thought I had the air out I installed the 180 t-stat (which does not have a hole). I was under the impression that the hole would help let air bleed out both during filling and running. Should I put a 1/16” hole in the 180 t-stat as well?

2 If I do have air in my system, do I have to drain and start all over, or can I just burp and continue filling?

3 Where do the air pockets like to hide?

1. It seems to help to have the hole. It will slow down how long it takes your engine to heat up, but i doubt it would be noticable. So yes drill the hole.

2. Just burp

3. idk Engine I'd suppose. They are supposed to work their way out of the system via the radiator. Make sure you keep fluid in the overflow tank to replenish the space from the air leaving.

You should be able to start the engine with the thermostat cap off and see the coolant flow. See what you can do to try and burp the system.

What I meant to say is, if the fan is running at full speed and the engine is hot,then your check engine light is functioning normally.(If the fan was running and the engine cold,then that would not be normal).Ordinatley it should go on some time after 230 degrees.Im thinking as its aproaching the red zone (someone correct me if Im wrong about that).Other causes could be a fast Idle (timeing is off) or vacume leak (causeing a fast Idle).

James Bond 007,
I now get what your saying...thanks for the good info!
The idle is around 2000rpm untill the engine temp gets around 110F...after that point it drops to around 1100rpm i believe. I havent checked the timing or for vacuum leaks yet, but if all else fails I certainly will.

Thanks again for your help and promp replies!

I will give an update on Monday

If you're idleing at 1100, you prob have a vacuum leak

Hey guys,

ok, so heres the update.

First of all, one correction...the car idles at about 900rpm when its warm (160ish)

Got home from work and checked the temp gauge/temp light only to find that the gauge is working but the light isn't...Great!. I then tried to burp the system but was unsuccessful. If the engine is running and i open the thermostat cap, it gushes coolant. I assumed the worst case and that there was a clog in the line. I detached both radiator hoses and flushed toward the engine through both. Not sure if it made a differenct because after the flush i realized that if i open the radiator cap while its running and then open the t-stat housing cap it won"t gush out. My new approach was to have a buddy cracking the cap open then closes (mainly open), while i poured water into the thermostat housing.
This seems to have worked so far. After he reported no more air coming out of the front and no more "hissing", he closed the radiator cap, i topped off the thermostat housing and capped it before it started to gush. So now the car is full of water (no antifreeze), and no thermostat installed.
I have run it for several hours now with no severe overheating. It primarily will run at about 150F, and occasionally climbs to 220F. It seems to only stay up there for a few seconds, but falls quickly back to 150ish.
I have not gotten to check the engine code yet, but will do it this weekend. I will also install the 180 t-stat (now has a 1/16" hole in the flange) and see what happens.
I am worried because 150-220 seems pretty hot for not haveing a t-stat in it.
Is it common for the temp light bulb to blow? Or do i have a bigger problem?

Any thoughts?

Thanks!! I'm much happier now because I feel there is probably no head/gasket problems...(right?)

Hi Guys,

I got similar trouble with my 87GT.
When i removed the thermostat, it was running quite OK but still, sometimes, with high temperature.
Everytime I installed the thermostat, it overheated very quickly.
My cooling system was brand new (new radiator, new stainless steel pipes under the car, new housing).
The only thing left was the water pump. It did not leak but I decided to dismantle it and it was this b......t plastic propeller that was slipping on the shaft but still with some resistance.
My conclusion was: when the thermostat was out, the resistance of the cooling system flow was not that high and the pump could let the water flow. When the thermostat was in, the resistance of the cooling system flow was higher and the propeller was slipping.
I replaced the pump and everything was OK (also drill a hole in the thermostat)

Another important thing when you refill your cooling system: you should put your heater to the maximum in order to fill your heater radiator (inside the car) properly and avoid any air in your circuit.

Hope this helps

------------------
Bernard
Fiero V6 GT 1987 (Manual)

BL3200,
Thanks for the info. I have suspected the waterpump for a while but didnt want to dive into it until I was sure there was no head warpage, block crack, or blown headgasket. Since i was able to run the car for a few hours withouth any major overheating (still no t-stat), i think its safe to say the motor is ok.
Any other ideas or test i can do to verify the motor is tight internally?

Just one more question, doesnt the coolant always flow through the heater core? and when you turn the heat on it turns the blower on and cools that liquid, but doesnt open up more flow?

Thanks for the encouragement!

quote Originally posted by jdilullo: I am worried because 150-220 seems pretty hot for not haveing a t-stat in it. Is it common for the temp light bulb to blow? Or do i have a bigger problem? Any thoughts? Thanks!! I'm much happier now because I feel there is probably no head/gasket problems...(right?)

idk about the temps. I wouldn't be over concerned. At some point the tstat is wide open anyways so yeah

Temp bulb - pull the 5 torx screws off the back cover of the dash and most likely the problem is the bulb's cap holder isn't making good contact witht the printed circuit board. Bend the wires to try to make them make good contact.

Blown head gasket - prob not.

Yes, the heater core always has full coolant flow. The Cold/Hot lever on your control panel simply swings an air door that varies the amount of outside air through the heater core. If you trace the heater core lines you will see there is no valve to stop coolant flow.

Is 900rpm at idle normal? or high?
there is a "bypass?" hose under the platic pipe that comes out of the air clean that attached to a hose which snakes inbetween the motor and the firewall...the end of this hose has a flange on it and is plugged into nothing...could this be the cause of a bad idle? or a code 32 (egr system)?

I will test the car today with the t-stat and watch for overheating...the car now has only water in it and I am affraid of causing rust. What is the best way to get some coolant into there (without having to go through the aweful burping situation again!!)

Thanks again all...how often do you all drive your fieros?

Results:

Test drive with t-stat failed...

At first it was great, i installed the thermostat (180F with 1/16" hole), the thermostat housing was completely full. Started the car and removed the radiator cap, no overflowing and couldnt fit any more water in there. The overflow was a little lower than it was after yesterdays test drive (i figured the radiator had done its job and exchanged air for water. I topped off the overflow and waited for it to warm up. It took a several minutes to warm up and the intake manifold was cool to the touch. After 15-20 minutes of driving (80deg weather), it overheated. It started to creep toward red so i pulled over and popped the hood. The overflow tank was overflowing out of the cap and the temp gauge continued to creep up into the red about mid way. After 10 minutes of sitting with the fan on, trunk and hood open it cooled back down enough to get me home. Fortunately i was only around the block!

So i will try the hanger in the water pump thing to see if it does have a slipping plastic impeller.

Other thoughts:
1 Could the overheat have been a result of no antifreeze? (boiling water?)
2 Yesterday without the T-stat it ran around 150 and crept up to 220 a few times, and today with the T-stat it ran around 190 and crept up to 260ish. The trend seems to be the same.

My next goals are to:
1 Replace the temp light bulb
2 Check the water pump with the coat hanger method

At 15 psi water boils at 257. I don't think you have an issue of water boiling. A anti-freeze/water mix does cool better than just water however it's not a huge huge difference.

There must be something bigger wrong with your cooling system. Impeller or radiator?

So i have some Great news and some not so great news!!

Great news:
Pulled the waterpump and it had the damn plastic impeller!!! WTF (who thought that was a good idea) and oh yeah...It slips like it was never pressed on to begin with!

Not so great news:
I sheared the alternator bolt that was in the way. So I removed the alternator mount so i could try to drill the bolt out while the alternator remained in the car...drilled all the way through the bolt, used my screw extractor and "SNAP", the screw extractor cracked off inside the bolt!
So i removed the rear "tie rod?", pulled the alternator out of the car, and if i cant get it out tomorrow im just gonna replace the alternator and leave the broken bolt i the ear!

Geeze...a lot of work and some speed bumps, but the plastic impeller really made the feel relieved, finally somehting made complete sense!

Thanks again guys for all of your help and suggestions...i'll post again when i get some more time in!

Rodney dickmans 210/200 fan switch ($19)
OR
Rodney dickmans 195/185 fan swtich ($24)
OR
Fiero Stores 200/185 fan swtich ($45)

Anybody have any input or suggestions?
Thanks!

$19.00

New water pump is installed, replaced the alternator as well. I will fill the system tonight (weather permitting) and report back with the results soon.
Thanks again all!

I am having a similar problem with me 87 SE 2.8 I drove to work this morning and when I slowed down to turn my temp shot up to 240. When I stopped, the coolant was spilling out the top of my overflow container. I parked on an incline, so the back of the car was higher than the front. Let it cool down with engine off and when I opened the Thermostat cap the fluid was completely empty in the chamber. Filled it and started the car. Shut it off after 5 seconds. Opened Thermostat Cap and level went down. Did this three times and it finally stayed full. Let the car sit and idle for 15 min and no change in fluid level. Keep in mind I pulled the Thermostat out, the temp stayed at 110 or so all the way back home (15 min) and as i turn to go down my street the temp shoots up again. i backed in my driveway, which is inclined, so the rear was higher than the front. Fluid again pouring out my overflow container. I opened the Thermostat cap and the chamber was empty again. WTF??????? Any help would be appreciated.

At this Point I would start at the first posting in this thread and answer all the questions that were put forth. Post your answers and then get some further advise... water pump check, crushed pipes, back flush, oil contamination............ etc.

Mark

------------------
Mark
In the Great Northwest!

Well it was the water pump...replaced it with a $35 unit that had the aluminum impeller!! Car runs great and doesnt overheat at all...runs around 170-190 when driving and goes up to around 220 at stops (after a few minutes). occasionally at a stop it will go up to 235 untill the fan comes on then back down to around 190.

Who made the plastic impeller water pumps?? was it GM or aftermarket?

Anyway...the plastic impeller waterpump is hard to detect because it doesnt weep, squeel, or leak. On top of that...without the t-stat it in pumps fine (in my case) and will even pump fine untill it gets hot.

I hope anyone else who has overheating problems considers replacing the water pump...its not that bad of a job.

Advice for waterpump change:
1) place a garbage bag over the fiberglass insulation to avoid a nasty rash
2) clean the area very well before beginning
3) hit any stubborn bolts with penetrating oil instead of muscling them out (i sheared my alt adjusting bolt this way and ended up replacing it anyway)
4) rtv both sides of the WP gasket
5) clean all bolts to the best of your ability and use a q-tip to clean out (not in) the threads in the block
6) carefully scrap all old gasket off
7) DO NOT OVER TORQUE the bolts (a broken bolt in the block or a stripped tap in the block would SUCK!
8) Let the RTV seal for 24 hours...do not rush it or its back to square one
9) flush the cooling lines after the job is done to clear any gasket pieces that my have fallen in (do not flush into the radiator, disconned the radiator hoses before flushing

I really hope this helps some people cuz i know how much is sucks to be without our fieros!

Thanks again to everyone who posted!

Thanks for the follow up.

Cool you have your problem put to bed.

Have fun - drive fun - but safe!