Hi, hope someone can help me out -- this one blows my mind.

85 IROC: Ever since I've owned this car I have been plagued with overheating problems...

Bone stock, new water pump, new thermostat (stock temp), new hoses, new belts, new fan (relay works,) and the radiator was put in back in 2000. Airdam is in good shape...

The temp just seems to rise and rise -- not so much when moving (it still gets too hot when moving.) Shoots up quick when in traffic or stopped -- I've never picked up fast food in this car ;-).

The temp seems like it wants to stay around 220-230 but after a while the system can't maintain it any longer and it just goes up (would pass 260 if I don't stop it.

What could cause something like this? Bad radiator from the start? It did have one BAD overheating incident in the start after the radiator was put in -- the thermostat froze right after... Could it be a bad head gasket? The oil never has antifreeze in it -- never smokes when I gun it, and I never see steam from the block or antifreeze where it shouldn't be...

The only odd thing is that the radiator leaks from the cap when it gets hot -- never goes into the overflow tank. I have replaced the cap three times, this one is even a higher PSI. I always make sure the fluid is always topped off...

Any ideas?

Stefan

 

was the radiator cleaned or was this a replacement radiator, whil the engine is idling (cold) can u see the coolant cerculating in the rad?
i'm thinking that there is a restriction either in the block or rad since every tthing else has been changed.

 

The radiator was new in 2000. Yes, I can see coolant flowing with the cap off (it arches from the top hose, should there be more pressure?) When the water pump was changes we never really flushed the system, just topped it off after (it's mixed.) Do you think flushing the system will really make that much of a difference, or do you think a new radiator is in order?

Thanks for the help...

Stefan

 

Is the plastic shield that goes from your nose to the area in front of your air dam still there. I have several friends that do maintenance on there cars and leave that peace off and next thing you know their overheating................just a thought.

I would also stick to your factory rated cap.

 

If your system is not maintaining pressure overheating is a definite possibility. Find out why it is leaking, if it passing coolant it is releasing pressure. The common problem with stock rad's was a crack in the plastic tank down from the cap. Remember that pressure increases the boiling point of the coolant, a loss of pressure or zero pressure will cause premature boiling. Also, do not rule out an intermittent fan relay. As I have posted numerous times they are notorious for working sometimes and not others. The contacts burn and they will fail at the most unexpected times. Spend 16 bucks and get an OE relay. New ones are redesigned and more reliable. Even if the relay is bad, it should still maintain pressure and FILL the recovery bottle. I would also stick with an OE radiator. I have worked on quite a few TG's with cooling problems and I have found the GM replacements to be among the most reliable and best constructed.Some guys don't like the plastic tank, the OE on my 89 rock lasted 11 years.

 

head gaskets.

 

I can't believe no one mentioned this GM designed the cooling fans to come on at a very high temp for emmisions reasons,I guess it burns up all the fuel in the cylinders or some crap . Anyway you can get a Hypertech fan switch that lets them come on earlier , there are two different temp settings you can get , I live in Florida so I got the one that comes on sooner . A lot of people just install a switch so they can turn the fans on any time they want . There is a whole lot of info on this either on this site or f-body.com . Mine used to drive me crazy sitting in traffic watching the temp gauge climb! Since I got the switch , no more problems!

 

Like the post above me said I have an 84 l69 carburated auto fully stocked the fan kicks in at 230 and off at 200 I have the shop manuel says that also ,32000 miles on the car and still going strong
Its rarely drivan Iv put a 180 themostate last year but the cars engine ran erratic when it hit 180 changed back to stock 195 cars engine purrs like a kitten I want to try to run a maual switch and keep it at 195 if posible but I dont know how ? Have someone on this board had this car with the same problem and solved it ?

 

It is on here , not f-body. On the home page go to Tech Central , then click on Technical Articles scroll down to GM F-body Electrical Coolant Fan Specs and Mods. This will tell you everything you need to know!

 

I just wired the fan to a toggle switch and put it on the dash....works great...i control when the fan comes on and goes off....never fails. Cost me only around 8 dollars in parts and some time....if you go that route, then just dont leave your fan on in a parking lot for 30min...you wont go anywhere after you get back to your car...but this way, my car never goes above 180.

 

1990, While I agree with most the info Willie supplied on that article(GM F Coolant Specs)there are a couple of points I disagree with. He states that these engines will run efficiently at a temp lower than 195. They don't. A 50-50 mix of coolant and water under a 15-16PSI pressure will boil at around 265 degrees. The stock dual fan setup will kick the primary on at 220-225 deg., well below the boiling point of the coolant. Another thing to consider is that lowering the fan temp turn on will cause more cycling of the fans and a much increased load on the charging system. The end result of that is premature failure of the alternator. I have tried all the different stats and different fan turn on temps and found the stock setup works the best. As a point of interest, Hypertech and Jet charge $40-50 for thier fan switches. NAPA stocks 2 different switches, the stock at 238 and one at about 215 I believe. They cost $19. Part of the theory of running at 195 is emissions, but also the engine will run more efficiently at this temp. The entire engine management references itself to a target temp of 195. Changing it to a lower temp just makes it less efficient.

 

Yes I agree it is not all 100% accurate , but before I put my fan switch in , driving in stop and go traffic in the middle of summer (actually most of the year here in Florida) the temp would climb way up around 240 . And always at least 220 unless I was moving.Since putting the fan switch in it has never gone above 220 and usually runs around 190 ,except during the winter at night it stays pretty low,but still once it reaches a certain temp it runs great.As far as the cheaper fan switches go I did not know anyone made any except Hypertech or Jet at the time I bought mine ,this was actually one of the first mods I did to my car besides the K@N filter.I even bought the Hypertech chip wich now I have read many times on many sites it is crap!

 

about the switches, where are they connected to the system? i just got the '86 last weak and already flushed the system and changed the stat to 180, the 160 was stuck closed. this only stopped the problem of overheating on the highway (the air dam was intact but u know....), i personally believ that when my fan comes on, the car is already on its way to cooking over (like 1990 GTA) to make matters wores, the fan only seems to work intermitently. asside from swapping in a higher CFM fan (2000+) i would like for it to come on a bit sooner or if it did come on at the stock temperature, be able to cool the car down it traffic. i can deal with the emissions test but it sucks to have AC and not be able to use it except at 55mph, where i dont need it, thanks

 

Do you have a single fan or dual fans? If you have dual fans the secondary one should come on when you turn the AC on . Before I got my lower temp fan switch my car ran cooler with the AC on because of the second fan . The fan switch on my car is in the head between the back two cylinders on the passenger side,could be different on yours I know they changed little things throughout the years.Like I said I love my lower temp fan switch,no probs at all!BTW when I thought my fans were bad I bought new ones , you just get the motors and have to use your fanblades , they were only about $20 from Autozone with a lifetime warranty.

 

It's the stock 85 setup -- one fan... I just replaced it with a new one (for the second time.) It fires up when it's supposed to -- but really doesn't help that much...

I'm still baffled -- how could the system build so much pressure that it keeps leaking from the cap? (Is it possible that the lip of the rad is warped?)

I really need a solution this weekend... What should I do?

Take it to a shop and do a chemical flush?

Buy a new radiator and put it in myself?

Say screw it, because the head gasket might be bad?

BTW -- what are the symptoms of a bad head gasket? Like I said in the beginning, no exhaust smoke, no steaming from the block, no antifreezes on the block, and no cross contamination of oil/antifreeze... I'm not a mechanic by any strech, but if it was bad I take it the pressure on the crankcase side of things is much higher than the little ~15psi of cooling system. If the pressure leaks into the cooling system wouldn't that cause the leaking from the rad cap?

Thank again for all the help!

Stefan

 

Stefan, generally you will know if a head gasket goes. You will see steam and usually smell it because of the proximity to the exhaust manifold and heat from the head itself. If it fails inward towards the cylinder it will either fill the cylinder with coolant and the engine will stop. Liquids cannot compress. Also you may see evidence of coolant in the oil(milkshake look to it). If it is confirmed that a leak is occurring at the radiator cap and you have tried a different cap then you will need to replace the radiator. The system MUST be pressurized to work properly. I have never taken my fans off(lucky so far), but is it possible to maybe install the fan blade assembly backwards? One thing for sure is that you must get the system to hold pressure. Any boilover or overheated coolant should land in the recovery bottle. If you are going to change the rad I would suggest switching to DEXCOOL. Take out the stat and do a good flush and then depending on the coldest you expect run the mix accordingly. Also use distilled water or you will defeat some of the properties of the coolant. According to Texaco(they invented Dexcool for GM) you cannot have more than 10% of the conventional left in the system. Kepp us posted,Dan

 

Maybe your temp gauge is inaccuarte.

 

thanks

 

If someone someone moved the factory set timing this can cause overheating check the timing

 

Thanks everybody for the input - and Danno, you raised my spirits quite a bit... My friends and I have put way too much work and cash into this car trying to ressurect it, only to have it shot down.

Anyways, when I was messing around with the relay (I bought a new one BTW to be safe, hell it's only 5.99,) I noticed something funny with the fan wiring -- a nice big tape buldge in the cable cover. Turns out when the last shop replaced the original fan motor they for some unkownst reason cut it out and used butt connectors to put it back together (as someone mentioned, backwards...) I jumped the diagnostic connector to fire the relay and looked at the rotation... Suprised my new fan survived the small trips I've made -- not to mention blowing nice hot air INTO the radiator... (I feel dumb...)

HOWEVER, it still runs HOT... Much better, but just sitting around idling can make it go up toward 240 -- too hot for me... This was after making sure the air was bled out and fluid topped off...

Then we commited a fuel injection sin -- pulled the thermostat... (mainly for sh*ts and giggles) Actually ran stock temperature -- never budged from 220, unless we beat the crap out of it... This was during a hot/humid summer day here... Just drove home tonight (cooled down a bit, still humid) didn't go over 180 -- highway driving...

I know this may mess with mileage -- but this saves me from buying a new radiator right now -- cash it tight (broke college bum.) When I get some extra cash I'll drop a new radiator and thermostat and see what happens...

Thanks again everyone!

Stefan