Question about 1986 Pontiac Fiero

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Overheating Fiero I have a 1985 Pontiac Fiero that is overheating after being driven for a while. The coolant is being blown out of the reservoir tank and is not being pulled back into the radiator. It does this with or without the thermostat in it. The cooling system has been flushed and a new radiator cap and thermostat housing cap installed. Also have noticed that after being driven, the pressure in the system does not bleed off and will not pull any coolant back into the system from the overflow tank. I have "burped" the system several times from both the radiator and the thermostat caps. Any suggestions?

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  • ceaves5 Feb 25, 2009

    I forgot to add that this is a 1985 Pontiac Fiero with a 2.5L 4cyl. engine with auto transmission. Any help will be greatly appreciated.

  • ceaves5 Feb 25, 2009

    Also the water pump was replaced and has been checked to make sure it is circulating.

  • ARFIEROGT Mar 19, 2009

    Hello, in May 2007 I bought a 1985 White Fiero GT with 32,000 on the odometer for $3500. I drove it for 500 miles, with little problem. First thing I found wrong was the wipers as I had to drive it in a tremendous storm. Installed new ones. The next day I had a passenger front brake problem, no pads. I also took the car to Midas dealer near me to re-do the air conditioning. Well they installed maybe two O-rings from a $30 kit and took it out to see if it was charged. Guy brought it back and took my money and I left to go pick up brake parts. Suddenly I noticed that the clutch pedal was kind of loose, also as I started to stop the brake pedal went to the floor. The guy that took my car out for a test must have ran it into the ground, as I was only able to make it to the parts store, and pissed off. I had to purchase a new front right caliper as it locked up, order clutch master and slave cylinder, brake master cylinder, and not to mention the tow truck ride to get the car home!

    As each part came in at the stores I would have to decide where to start, first was a not so nice of a phone call to Midas.

    As I was inspecting the rest of the car I noticed that the back three plug wires came rightoff the plugs, exept the top of the plugs were still attached to the wires. Also the rest of those plugs were rusted in from not having the drip flap. The distributor was no better, old and dryed out in and out. The rotor shaft could'nt even turn by hand. The air cleaner was even scary, it just crumbled in my hands. It now has a K&N.

    After ordering plugs, wires, coil, distributor cap & rotor, and the other odds and ends. This was just in the first three months with no driving.

    I also did some body modifications too, such as a taller (7") wing with an aileron between the stands. Also the trunk lid lost its small bump for a Hemi Cuda 6 Rack scoop in reverse, and a 2,600 cfm blower fan inside.

    Also on the rear deck at each side are intake Snorkel scoops, also with 750 cfm fans inside. I also cut some old front fenders and bonded them to rear fender humps.

    The sides behind the doors have 12" tall scoops with 750 cfm fans each side. The battery is in the front trunk compartment, with a cut-off switch and fuseable link.

    The front hood has air inlets and outletsfor the radiator. The fronts and back edges of the tires also have inlets and outlets, which are all from 80 series Trans Ams. The nose has an amber Knight Rider light, and the turn signals have been lowered and their old space is now used for SRB dual fog/spot lights. In the nose scoop there is twin amber fog lights, and an extended airdam.

    In the rear the whole lighting system has been changed to LED's. Top of the rear window is 49" of LED stop/turn, and the rear bumper lookes like a Corvette now with two 4" 64 LED on each side for run/stop/turn. The backup lights are halogens now where the red reflectors were in the bumper.

    I have 14x7 American Eagle rims with Uniroyal Liberators which provided the extra height I needed, was 4" off the ground and now is 8". The 23 year old Goodyears did a BIG SCARY NUMBER to me. The drivers rear de-laminated on the highway and wiped clean the additions to that side and sent me into a 360* over two lanes and then over the side of the highway 300' down. The repairs are still in the process, but the car still runs. Infact heres another journey with the new tires. First I must exclaim that at all times with the old and new rims I had 1/2" spacers up front and 1.25" in the rear, this was to finish the wide body look. Anyway I was out to try the new treads and 100 miles out started getting a thump-thump-thump noise and thinking it was a new tire going flat. So I stopped at a station, checked everything I could see and hear,came up with nothing so I decided to continue on a less used slower road. I kept going and so did the noise, but now it was jolting movement. I got another 25 miles to a small town when BOOOM-CRASH-SCRAPP the drivers whole wheel assembly fell off and hit the damaged side of the car and I and the car fell to the pavement and just missed a graveyard by inches rolling on the brake rotor. Luckly on the other side of the road some guys at a used car lot saved my tire from hitting anything. Well I was close to my destination and had it towed, turned out that lug nuts were lose (not sure if human error) and a few studs on the hub broke. Now all that is fixed and the weather is getting fine,

    I'm working on her still but am getting a problem with the cooling system. I have drain and cleaned and inspected everthing, because it seems trouble is following me. I did the burp treatment and also a little trick a mechnic told about drilling 3 1/32" around the inside edge of the thermostat and to use some gasket sealer on the cap surfaces. Everything thats been written on or off the net I have tried. At this time I drive maybe 25 miles and the cooling system trys to fill the overflow container. There has been leaks in this area which I removed the bottle and seems to be coming from bottom nipple. I tried superglue around the whole bottle with no results. Everything looks right, but they are decieving. I don't want to brake down again, as I already in the past two years have spent enough in towing for another car.

    Any Ideas would be greatful and I provide some pics to a email address, Thanks.



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Well fieros are very different cars you need to fill collent in a speical way so air doesnt get in the lines most fiero owners do not know this but it very important The best way to tell it is for wikipedia
Cooling system issues
With an already hot normal operating temperature of 220 °F (104 °C) prior to the recall switching to a 195 °F (91 °C) thermostat, the mid-mounted engine utilized long pipes to carry coolant to the front-mounted radiator. This demanded that a special coolant filling procedure be followed to prevent severe overheating. Simply pouring coolant into the thermostat housing (on the engine) would leave an air bubble in the radiator, while adding coolant just to the radiator would leave an air bubble in the engine's coolant passages. Proper procedure (with engine idling and the thermostat removed, filling the thermostat housing, burping the bubble out of the radiator by cracking open the radiator cap until coolant exits) must be followed in order to ensure an air-free cooling system.
A second problem has become common as more Fieros are being serviced by shops unfamiliar with their design. The under-body coolant tubes are positioned in such a way that a casual glance beneath the car will not suggest their fragility. As a result, many have been crushed by shop lifts, resulting in a near complete lack of engine cooling. The age of the car means that even GM dealerships may now be unaware of the proper jacking methods.
Lastly, the absence of a spare tire (at the front of the car, right behind the radiator) could have an effect on coolant system performance. i dont know who wrote this and i dont take credit for it

Posted on Nov 19, 2009

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The 1st answer is mostly correct. All except for the 'spare tire' comment. In addition to the crushed pipe inspection, there is also an air dam/front spoiler underneath the bottom of the radiator up front that does more than you might think:

1st: It creates an area of higher pressure in front of the radiator forcing more airflow at any given speed through the core.

2nd: It creates an area of lower pressure behind the core so that airflow through it is increased at any speed.

These tend to be bent up from many instances of owner's bottoming out over the last 30 years.

I have also had the pleasure of owning an '86 GT V6 that had the coolant fan motor, the coolant fan relay, and the temperature controlled turn on switch, ALL go bad. If you have a V6 with A/C (hope you aren't wasting your time on a heater & keys 4 cyl.), with the key on and the engine NOT RUNNING, push either of the 3 A/C buttons (MAX, NORM, B/L) and see if the radiator fan turns on. If not, go back to the engine compartment and see if the engine compartment air circulation blower is pushing air out of the silver pipe pointed at the distributor and/or rear of alternator. If it is blowing air but the radiator fan is not turning, then you have an electrical problem somewhere between the switch. the relay, and the elec. motor.

Worst case scenario, you have a blown head gasket and the engine is pushing combustion gasses at high temp. and pressure into the cooling system until it reaches 15 psi, then the front radiator cap opens and lets all your coolant out, causing a runaway overheating situation. If properly filling the radiator, and running it with the fan on doesn't keep your engine temps under control, maybe have a shop 'SMELL' your coolant at the cap/fill area. If they can detect CO or HC's out of the cooling system, then it looks like your heads need to come off. :-( Good Luck!! And HAPPY FIERO-ING!!

Posted on May 09, 2016

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Air cannot pass through the radiator efficiently if it cannot evacuate from beyond the radiator. The radiator is positioned in a manor that directs the hot air up and trapping it. I removed a section of the front hood making sure I did not get into the storage gasket area. I then bonded a fiberglass cowl induction scoop to cover the opening and to assist in channeling the hot air out from under the hood. Some have installed slotted panels. The best bonding material for any fiberglass is "Vette Panel Adhesive". It sands like bondo and is stronger than fiberglass. Keep it Cool!

Posted on Feb 07, 2010

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1 Answer

86 fiero overheating

Low on coolant, air bubble in coolant, water pump faulty, coolant fan motor/relay/switch/fuse bad, collapsed hose only when RPMs are raised, bad thermostat, any of these could be the cause. Low coolant and electrical issues are easy enough to sort out.
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It is best to be systematic about this. It could be either the water loss or the overheating which is the basic cause, either one could come first.

- there is a test for combustion gases in the water jacket, from a blown head gasket. This will very quickly cause overheating, and the excess pressure will blow the water out the overflow reservoir. If the car has already overheated and died, this is unfortunately quite likely

- the temperature sensor in the block may have failed. This will prevent the fans from running when the engine overheats, and you can see this. The fans are not driven by a belt. P68....

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Hi carl i had pontiac montana m1999 overheating after i travel like 40 km n all the coolant going back to the reservoir

Hello, if you've changed the pump. cap. and t-stat and its overheating still i need to say that just because you replaced those parts doesnt necissarily mean they work. Im mainly talking about the t-stat and cap. was this your first time installing a tstat? They go in a certain way. Make sure you put it in the right direction. Your vehicles engine might require you to purge your coolant system of all air. On some cars air will remain trapped in the area right at the tstat causing it not to work therefore not opening up and no t circulating the coolant. I would start there myself. If thats not the case, next id flush the radiator. I would like to know what the problem symptoms were wich led yoy to replace those parts please.

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Hello, bigdaddypsl and thank you for asking your question on Fixya!

Here is a simple process that will walk you through a few steps that will pinpoint the overheating problem on your
2002 Pontiac Sunfire, without even using any tools. It has helped millions of people, and I am certain that it will help you, because I wrote it for people in your exact situation.
How to diagnose your overheating
2002 Pontiac Sunfire

Get more great money saving tips and tricks about your vehicle from:

Thanks for the vote, and good luck!

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My 1999 Grand Am GT has muliple problems but rite now I'm focused on it over heating. It has a new water pump, new coolant tank, and new thermestat. My car has water flow but is still overheating. Im...

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