2005 Pontiac Grand Prix Heater Core/Warped Heads


Asked by Feb 05, 2017 at 07:45 PM about the 2005 Pontiac Grand Prix Base

Question type: Maintenance & Repair

My car was overheating (to the point once
or twice that the car shut itself off).  I
continued to drive it until I absolutely
couldn't anymore.
I finally took it to a mechanic.  The
mechanic said the heads are warped, the
heater core is not working, and the water
pump is bad, and there was a line
connector issue in the transmission.
I let the mechanic charge me $500 for the
tests and to fix the transmission issue.  He
wanted to send the cylinder heads in to be
remanufactured ($1700), and I couldn't see
myself letting that happen.  I paid $60 for a
water pump and heater core, and $350 for
new cylinder heads (these prices include
tax and shipping costs).  I've gotten to the
point where I'm starting to question
whether or not the mechanic was right or
I bought the car used from one owner last
April.  The car hasn't had heat since I
bought it, but the A/C will freeze penguins
out of Antarctica.  The car started
overheating after sitting for 2 months in an
impound lot (July-early September).  I
moved to a new state, drove the 350 miles
with no over heating issues, no leaking
issues, nothing.  In October, the
overheating started.   I changed the
thermostat - that didn't fix the problem.  I
switched the type of 50/50 I was using -
that didn't fix the problem (yes, I flushed it
first).  I changed the water pump - that
didn't fix the problem.  I'm working on
changing the heater core this week, then
the cylinder heads.  I'm just going to take
out the old ones and put new ones in,
instead of sending them to a machine
shop(I assume this won't hurt anything in
the engine?)
I guess what I want to know is: will warped
heads, even if the water pump and heater
core are new and working properly, cause
the car to continue to overheat?  Also, how
do I know for sure the heater core is bad?
The mechanic said he wasn't sure if that
was going to fix the problem, but he would
try it just to be sure.  There is no fog on the
windows, there are no puddles on my
floorboards and I haven't had heat since I
bought the car, but the car hasn't always
overheated.   I moved to a state where
Winter actually happens, so I need the
defroster to work for winter weather and
rain.   I need advice on this before I go
ripping my glove box out and the inside of
my car apart.  I have a 2005 Pontiac Grand
Prix, base model, no mods or anything like
that.  It is a V6 with a 3800 engine.  

5 Answers


The mechanic I took it to did a CO test, and said the heads are warped. When I start the car, there is heavy white smoke coming out of the exhaust pipe, but only while the car is sitting. While driving, the smoke goes away almost entirely. The car has to be driven at least 10 miles before it even decides to start warming up at all, but once it's warm, it goes from warm to red zone hot. Will the warped heads cause the car to continue to overheat, even after all the repairs I've already done?

1 of 1 people found this helpful.

Ah, okay. Thanks a lot. I asked the mechanic for details, but he just kind of beat around the bush. Also... one more thing since I've got you... The mechanic said the heads are leaking into the camshaft (I believe he said camshaft or crankshaft). Does that mean I will also need to replace that part, or...?


I'm going out on a limb here since I haven't seen your Grand Prix. But the 3800 V6 is a real workhorse. Block and heads are cast iron. I honestly doubt that you warped the heads. I'd be more inclined to suspect that the upper and lower intake manifolds are warped from the overheating. They're aluminium. If you pull the oil dipstick and see white milky "goop" on the dipstick it's most likely the intake manifold gaskets leaking coolant into the crankcase. Not a blown head gasket. The 3800s rarely, if ever, blow head gaskets. It's also very hard to warp a cast iron head! If the intake manifold gaskets are leaking it's probably because of the overheating and the manifolds are aluminium. Do a cooling system pressure test. The cooling system should hold pressure for a minimum of 15 minutes. If no evidence of leaking can be found you probably have air trapped in the cooling system. This will also cause the no heat issue. I've found the best way to refill the 3800's cooling system after a service or repair is to pull the cooling system down into a vacuum. Again, the vacuum should hold for a minimum of 15 minutes. There's a tool for this that a reputable shop should have and know how to use. On the other hand a clogged heater core is also a possibility on a 12 year old car. But I'd try the pressure test and vacuum refill procedure first. I'd also get another mechanic. It doesn't seem like he's real familiar with these engines. One final thought. The computer system in these vehicles has a safety feature to prevent engine damage when overheating. The air conditioning is turned off and the computer begins firing alternate cylinders to help keep the engine cool enough to get you home or to the nearest service facility. GM boasts you can drive about 50 miles, at reduced speeds, this way and the engine won't be damaged. The non firing cylinders act as an air pump to push excess heat out the exhaust during the overheating condition. HTH. -Jim


There is no white, milky goop on the dipstick or in the oil. I've drained the oil, did an engine flush - no white milky stuff. I flushed the heater core - no heat still. I didn't think the heads were warped because I got the new ones and just no. Haha My car does do that when it overheats - it shuts the A/C off and all that good stuff. I don't know at this point.

1 of 1 people found this helpful.

Then definitely pull the cooling system down into a vacuum and refill that way. Sounds like you have air trapped in the cooling system. HTH. -Jim

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