Pontiac Repair: 99 Pontiac Bonneville, pontiac bonneville, water temp

Question
QUESTION: I have a 99 Pontiac Bonneville too and it is doing weird things like a previous person wrote about.

The dealer replaced the alternator, starter, I have gone through two batteries.

Another mechanic has had it and done a bunch of different things and when I get it back it seems to be fine for about a year then it starts all over again.

Right now the water temp red lines and then it runs rough for a few min

and either dies causing me to put it in neutral and coast for a while then restart and hobble to my next destination (possibly doing this several times)

or all the sudden the thermostat works (or something else) and the temp dives back to a normal range then starts creeping back up to red line again.

This cycle seems to be one or the other.

I suspect the thermostat but this isn’t the first year I have had this problem and the thermostat was replaced at least one time.

Most of my driving is around town so the thermostat doesn’t get much of a work out.

I do the other thing that is supposed to help also which is putting on the heat full blast and I get no heat at all out of the vents and it does nothing to the red lined water temp so that is useless.  
When it red lines then dives (after the thermostat kicks on I geuss) I do get heat while it is diving.




ANSWER: Hi Steve:

was this car origianlly low on coolant? if so does it leak it out on the ground? If not take out the engine oil dip stick and look at the oil it should not look white or milkey.. If so the coolant is either being burnt in the combustion chamer or is leaking internally in to the engine. These engines have issues with the upper intake manifolds warping and leaking coolant inot the engine. On the non supercharged engine. As for the thermostat It could be that it's not working. It does get a work out driving around town or on the highway thye don't juts open and close they constantly are regulating the water temp/flow between the engine and radaitor. as for the no heat I'm sure there is an air pocket in the system right now and it's stuck in the heater core. I would have the engine cooling system pressure tested. both cold and again hot. It may not leak when cold but will hot. other than the intake leaking coolant the rest of that engine is pretty much bullet proof not much goes bad on them ocassioanlly a lower intake will leak but really rare and I think I have only had 1 with a blown head gasket. Hope that helps some.... Good luck :}


---------- FOLLOW-UP ----------

QUESTION: The oil fill cap and dipstick not milky - looks good.
It did have a new manafold put on 2 years ago because it warped and let a bunch of water in the engine making it undrivable.  Surprisingly I found out 1 year later that they did not replace the lower intake manafold gasket when the manafold was replaced the reason I found this out was that it was running crappy again and now leaking water oil mixture and milky dipstick and oil cap.  I thought I was doomed but my mechanic replaced the oil presure switch and recomended the lower manafold gasket be done too. He said the upper manafold gasket was replaced but not the lower. Anyway finances (or lack there of) forced me to hold off on the gasket.  It ran great till now and I do not have milky oil.
Could a heater core blockage by air or scale cause this red lining?
I saw some other answer simular to my question where using a garden hose (at very low pressure) barely on back flushing then forward flushing the coolant system - I could try that.  The cycle where it redlines then dives to normal then creeps back up to redline is puzzling me and in the last two days it won't dive back to normal.
Or is the redlining more likely to be the thermostat or some other thing?


Answer
Try a new thermostat. They are cheap enough.you can try it with back flushing the heater core. you can also fill the cooling system with the heater hoses off when the coolant comes out of the heater hoses fitting put the hoses back on. that will push out the air in the block. then start the engine up and fill the radaitor up when it's full and hot put the cap on and top off the overflow bottle take it for a drive and see what happens. if it still overheats then you have to take it to somewhere to get it looked at. It may have another issue... good luck :}