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Discussion Starter #1
i have an older firebird.. 305 motor, 210,000 miles...

something is going on with the water temperature.. it starts up.. rises gradually to about 230 then drops and stays at 220 for a while.. then it will slowly go back up to the red zone (260) then sometimes for no rreason drop down to 210...

usually turning the heat on does not do much to help lower the temp.. but sometimes it does...

some times it works ok staying around 220 other times it fluctuates all over the place. going right up to the red zone..



i tried replacing the thermostat twice and both times it still does the same thing...



Things i have not done:

flushed system
changed heat sending unit


side info:
last year the heater core went (indicated by stuff coming out the defrost) I did not have it repaired - it was gonig to be expensive 400-500$ .. But the mechanic added some sealant stuff and that seemed to stop the defrost stuff coming out...

But i am not sure if this could have caused some of the present problem...

Its never actually broken down & overheaten.. but its gone as hot as the gage will go before i get it home - i do not dare to take it far now...



My question:

Would flushing the system do anything?

Do i bother to try the heat sending unit?
i thought the heat sending unit is a temp gage.. i dont know its the gage or inconsistent temperater fluctuations...




PS. This is my 'shitter car' i love it but dont want to spend a lot of money on it...



Any suggestions on what to try?
 

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SJ, you can try flushing the system and it could improve the over heating problem but I would not count on it. If the temp is going up into the red; you have some serious problems of most likely the head gasket kind if it is not an indicating system problem. Have you tried checking the temp with a IR sensing gun or meter? It is tough to get an accurate reading with a thermometer. If the temp guage is accurate, you may have a cracked head or leaking head gasket. Are you noticing a regular loss of coolant, oil in the coolant, or coolant/water in the oil? Those are dead ringer signs of this prognosis. I would suspect the radiator would boil over if you let the engine run with the radiator cap off.
 

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I think i would try a different temp gage and censer. Also do you have a electric fan or a clutch fan if electric the temp censer may be bad or th fan itself. If you have a clutch fan the clutch maybe bad.
 

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Discussion Starter #4
no fluid loss in fluid level and no signs on the ground..

have not seen anything in the oil...
i was concerned about a head gasket or cracked block?

after I replaced the thermostat today.. i took the radiator cap off and let the car run.. (5 minutes or so) it did not boil over, and i seemed to see the thermostat (or whatever) open up as i saw water flowing through the radiator.

gage:
it seems the gage is ok because initially the temp raises nice and slow as the car warms up so at least it seems accurate in the beginning..
 

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My sons Nissan 240SX used to overheat and the temp gage would be erratic. I flushed the system, changed sensor, gauge (entire instrument cluster) new fluid clutch on fan (yep a 1990 with a engine mounted fan with the engine in the right positon instead of sideways and it was actually rear wheel drive) and a few other sensors. Broke down and took the radiator out to have it chemically cleaned, and in the process the radiator was not able to have the tanks reinstalled as the aluminum tabs that hold the tanks in place kept breaking off, so a new triple pass radiator was installed in place of original single pass, new water pump also installed, radiator cap, and it still ran erratic on the temp gage. Pulled the head after finally having the exhaust analyzed and finding antifreeze in it. Never got oil in the water or water in the oil all this time, and it turned out to be a cracked head. I would suspect cracked head or leaking headgasket. Do you notice any white smoke not blueish or grey buy white coming out the tail pipe?
 

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Well if you flush the system it will leak. All that sealer will come out, plus more stuff that is plugging leaks you don;t know about yet. My bet would be water pump. I would bet that you will find the temp changes are at diferent RPM. If the water pump impelller is rusting away, it will pump better at some RPM's then others. May be time to figure out the plans for the car. Dump some money in, or off it to some young guy that would love to have a V8 Firebird to play with.
 

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I find that leak sealent more problems than its worth....its easier to replace the leaky device than to clog up your water jackets or Water pump....of course if its the heads you have bigger issues...

Replace the water pump, thermostat, heater core any hoses that look bad, etc....it will be less money than you think- shop around

Duc
 

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Discussion Starter #9
the reason for the expensive heater core was mostly labor.. i think the whole dash and stuff would have to be pulled...

cracked head:
so can i go get a simple exhaust test to tell if the head is cracked??


water pump:
I though if the water pump went the car would just straigh out overheat and/ or leak water


is there a way to tell if the weater pump is bad? (Fan has play in it???)


for couple hundred bucks or so i would do the water pump and would be willing to have a go at the heater core (not sure of the cost for the part)


but if i can diagnosis whether it is or is not a cracked head that would be good...
 

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Discussion Starter #10
ryan, FYI: the car is a strong great car.. i bought it 3 years ago it had a smashed front end... i drove it with a white bumper and red fender and white headlight cover for 2 years then finally decided to paint it when it turned 190,000 miles...


<img src=http://www.tractorforum.com/forums/attachment.php?s=&postid=39852>
 

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Discussion Starter #12
no pressure tests done and no real sign of smoke coming from the exhaust..

Also, the car runs great... no hesitation...not sure iof that means anything...



so is there an easy way to rule out the head gasket??? If i could rule that out.. id do the water pump and/or sending unit....
 

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Pressue testing is usually the best method of checking that. Most garages have the testor and I would imagine that perhaps Autozone or some other parts store may have one and can test is for no charge.
 

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HI
The first thing I would suspect is the goop that mechanic put in.
Does it overheat at slow speed or idle? Will the temp stay down
if you are at highway speed? Lots of things could do that. Just have to start eliminating them. A bad fan clutch will do that if you are in slow traffic.
Rodster
 

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Discussion Starter #15
overheats (or temp goes way up) at all speeeds.. regular side roads 40-50 or on the highway

slower or faster... but other times it will go way up and for no apparent reason.. drop back down to a normal temp for a while...
 

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sj
When you repaired the nose did you replace the water pump? Most of the time when the radiator is pushed into the fan the water pump will be damaged although it might not appear to be. We used to change fan, blade and clutch and water pump any time a car was hit hard enough in the nose to push the radiator into the fan.
As for the sealer, why? It would have been easier to run the heater hose around the heater core, although you wouldn't have any heat.
As for the heads being cracked or a bad head gasket, you can get a tester to check the coolant for carbon monoxide. Sometimes the leak won't mix oil/antifreeze. Sometimes it's on the exhaust side. The exhaust gases could be going into the cooling system and raising and lowering the temp. Especially if going faster doesn't cool it off. My 71 torino GT 351C will run a little hot if idling in traffic but as soon as I get it moving will come right down.
 

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Im just taking a stab, but have you noticed any signs of overheating other than what the guage says? Guages can be wrong, and temperature sending units can go bad as well.

When you say it has never broken down or overheated, that makes me wonder. It could be a bad radiator cap as well. Without the proper pressure, it could cause errant temperatures.

If I was suspecting a head gasket, I would look at the oil for condensation, or wick the throttle a few times with the radiator cap off. Alot of times, a blown head gasket will cause water to spew from the radiator as the RPM's increase, as the pressure has to vent somewhere. I call it the 15 second Isuzu Trooper test. LOL

I like mentioned above can see the sealant thing that was applied earlier as a problem too. Seems to me anyway that most of those sealers, stop-leak, etc. type things are trouble. Yea, it might take care of the leak, but look at what it does to the gasket, O-ring, seal, etc. Most are just a band-aid to mask a problem- not fix it.


Good luck, and keep us posted. It will be interesting to hear the verdict.

Greg
 

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Discussion Starter #18
Originally posted by Fusion1970
If I was suspecting a head gasket, I would look at the oil for condensation, or wick the throttle a few times with the radiator cap off. Alot of times, a blown head gasket will cause water to spew from the radiator as the RPM's increase, as the pressure has to vent somewhere.


Greg

ill try that pressure test..

i did consider rerouting around the heater core.. but did not want to go without the heat...

thanks for all the suggestions guys..
 

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Discussion Starter #19
ok still driving my car around short trips..


I took it about 15 miles and it was near red line by the time i got it home..

popped the hood and checked.. The fan was not going at all... now im no mechanic, but i would assume if the car is hot.. the fan ought to be going..

it looks like an electrical fan not belt driven..


i called an auto parts place and they sell a fan motor.. they said its usually the electric motor that goes..

is there any way short of replacing it.. to test this out?
 

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I think you should also have a temperature switch that turns the fan on/off. Another thing is if you have AC, when you turn on the AC, the fan should come right on, if it doesn't you know either the fan or temp sensing switch are bad.
 
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