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jazzmaster, ASE Certified Technician
Category: Pontiac
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Experience:  ase certified
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I have a Pontiac Bonneville 1999 that is leaking coolant.

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I have a Pontiac Bonneville 1999 that is leaking coolant. I think it is leaking only when running. I checked it a couple weeks ago (just routine check on level) & it was low. It had not been running hot though. I filled it to cold-line and assumed it was fine. It ran a bit hot the other day (not on red, but higher temp. gauge than usual) and I checked it later in the day after engine cooled & coolant was gone/extremely low. I refilled it to line and my friend (who knows a bit about cars) checked radiator and said it was 'dry' and also poured coolant into it. It ran great on my way home & way to pick up my child. Temp gauge was low again and all seemed fine. But I checked the level this evening when it had cooled and nearly all coolant was gone again. There was no leak anywhere under car in any place it was parked today. What causes it to leak when running and is it safe to temporarily drive it (until I get it fixed) as long as I keep filling it w/coolant? Should I be putting water alone into it? Someone suggested I keep the radiator cap loose, is that right? Is this an expensive problem? The car has a lot of miles (around 187,000) but it has been running great (I've only had it a few months). The A/C doesn't work, but otherwise it runs good and has been fine.  


More Info:  I have been driving a lot more than usual this week & it has been very hot outside last couple days.  I don't know if that has anything to do with it, but maybe its relevant.  Also, my friend suggested that if the car did overheat (the other morning when it did run hotter though wasn't in the red zone) then maybe the temp. gauge isn't accurate anymore if it was damaged.  It wasn't smoking though and drove well after it was just keeps losing coolant.

hi, check the oil and if it is a milky brown or overfilled ,the coolant is leaking into the oil ,this is a upper intake issue ,if the oil is getting mixed with coolant ,replace the intake gasket ,these cars do have problems with the intakes (plastic) warping .,so that will also need to be replaced ...guy.....
Customer: replied 5 years ago.
A friend of mine looked at it today and said the coolant is getting into the oil. He could smell it. It did not, however, lose all its coolant today as it did yesterday. It was full when I left home (I had to go somewhere) and while it did lose a bit when I checked it later in the day, it did not lose much. Also, very strangely, when we checked the radiator this time instead of being dry like the day before the fluid in the radiator looked green. My coolant is bright red/orange. I have never seen anything green in the fluids before. The radiator was not dry at all like the other day and all the fluid looked green. The A/C does not work in this car & has not been working/used in a very long time. Could an A/C fluid cause the green color though? I don't know why it would be in there (if no one used A/C in years), but I heard that it could cause a green color.
The car is still not running hot. The temp seems okay and if I didn't know there was a problem it'd seem fine as it performs normally. The gasket fix would likely be very expensive right? What do you think could cause the green fluid in the radiator? Is there any better temporary fix other than what I've been doing (keeping an eye on coolant and gauges etc...)?
yeah ,if the oil smells like coolant ,more than likely the coolant is getting into the oil through the intake this being plastic does warp and over time will mix a lot of coolant if it is not fixed right away,NAPA has a replacement intake manifold (upper intake) ,it may run you around 149 or so for the part,I would think that this should be fixed before the oil gets contaminated and possibly hurts the bearings ,the reason it may have not used as much today is that it is getting corroded under the intake and possibly not leaking as much but it will turn the oil a light milky brown color soon ,as far as the coolant looking green,perhaps some of the green antifreeze was added or sometimes it will look green(like a lime green color)the ac is no way connected to the cooling system,although there is a green leak detector for the a/c to find hard to spot leaks ,,but no way is connected to the coolant ,there is no additive that will work to seal the intake gasket, although there are chemicals at the parts stores which will say that they do ,and in the long run may cause problems ,such as clogging up the heater core or radiator ,so I would suggest getting a replacement intake manifold and fixing this before you run into other problems ....guy...
Customer: replied 5 years ago.
How much do you think labor would cost on a job like this? A friend told me it'd probably be at least around 500 to get the whole thing replaced, and maybe it'd be a lot more than that, does that sound right to you? I can't really afford a big job. If I can't get it done right, what would be the best (or least damaging) short-term fix? As of now the car is still running well. I know its a problem, but I've talked to a couple people (not "real" mechanics though) who thought the car could still last me a while in this state as long as I keep an eye on everything & don't let it overheat. thanks.
p.s. It really did look green (the fluid in radiator) to me earlier yesterday, but last night when it was cold i dipped a handkerchief in a wee bit to check the color of the fluid & it was reddish/orange normal color. So I don't think its green after all. Maybe it was a reflection or something earlier that I saw.

ok, the price of the upper intake is around -$ 129.00 at auto zone ,it may be more at other auto parts stores ,139-169,and the labor calls for around 2.6 hours,,so if someone is charging $60 per hour it may be as little as $300 to fix ,it depends what someone would charge for labor and if they bought the part they may charge you list which could be as high as 250.00 or so ,you could get the part and then see what they would charge you to install it also ,

as far as driving it ,as long as you keep a very close eye on the coolant level and the oil and the teperature you could drive it ,but if it leaks a lot suddenly you may hurt the motor ,dont let it overheat and look at the oil before you drive it (everytime),oh yeah sometimes the coolant will look like a lt green in the right light ....guy...

Customer: replied 5 years ago.
Hi, just one last thing I was curious about. Thanks for your patience. I've been checking the oil & coolant each day and before each drive & for now everything is pretty much staying the same far as I can tell. It is not overheating at all. I noticed though that when I check the oil w/the dipstick it shows as being a bit above full (it isn't going up at all its pretty much stayed the same level & same 'normal' color for days now). However, the oil gage in the car is not showing full. It is showing about an average or halfway full amount. I trust the dipstick cause its actually in the tank, but can you think of a reason why the gage is so different than the level I see on the dipstick? If there is coolant in the oil would that distort the gage reading? thank you.
yeah, the gauge may show different as the viscosity of the oil may change due to moisture in it (coolant) so rely on the dip stick ,just keep checking ,as it may be a slow leak and wont show until onday it may overheat or the color of the oil will be milky...guy...
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