2002 Grand Prix SE--Is my lower intake manifold gasket failing?

[Teraforce88]

Hello from Indianapolis!

I inherited my Grandmother's silver 2002 Pontiac Grand Prix SE in the summer of 2012 with just under 43k miles. It has the 3100 SFI V6, whose notoriety for blowing lower intake manifold (LIM) gaskets was unknown to me... until one very cold morning in December 2012, when the "Low Coolant" light came on for about 10 minutes. The engine temp was normal, and the light never came back on. The coolant was low, and it appeared to have DEX-COOL, based on the orange color. I topped it off with some green coolant about a week later, which I later discovered is a VERY BAD idea. Around the summer of 2013, I had Firestone Auto Care flush out the cooling system (since I had no idea if the coolant was ever changed in my car to begin with) and refill the system with the normal green stuff (because of all the bad things I read about DEX-COOL).

Fast forward to today. About a month ago, I removed the radiator cap for the first time, and discovered that it was covered in brown sludge, which may be a sign of a LIM gasket failure. I cleaned off as much sludge as I could, although a little bit of it is back on the cap. The underside of the oil cap does not appear to be milky, foamy, or covered in mayonnaise, however. The oil level seems to have gone up slightly since I last changed it (about 1 month/1500 miles ago). As for the coolant in the tank, I *THINK* it looks a bit grayish, but it's VERY difficult to see the color or the level of the coolant because the tank isn't very translucent to begin with.

Here are some pics:

3100 SFI V6 by Teraforce88, on Flickr


Radiator Cap Underside 2 by Teraforce88, on Flickr


Radiator Cap underside by Teraforce88, on Flickr


Radiator Cap side by Teraforce88, on Flickr


Radiator cap removed by Teraforce88, on Flickr


Enging oil cap underside by Teraforce88, on Flickr


Engine Oil Dipstick by Teraforce88, on Flickr

 

[02NavyBlue]

The brown sludge is simply a result of dex cool. Mixing the two will cause lots of sludge but it seems you had it flushed soon enough. Even dex cool alone over a decade will cause some sludge from being exposed to air. If that little bit is all you saw I wouldn't be worried. If it doesn't overheat, and if you add coolant and it doesn't drop I wouldn't be worried about the intake either.

 

[lewis1952]

I would keep an eye on those strut mounts. That's a lot of rust.

 

[02NavyBlue]

My old ones were a bit worse lol. I flaked nice sized chips off mine before replacing them

 

[BillBoost37]

Being a 3100, I would automatically say yes on the intake gaskets. They are maybe a bit more common than the 3800. Make sure you get the metal frame gaskets. And.. keep the pushrods in order, they are different sizes between exhaust and intake.

 

[Teraforce88]

The brown sludge is simply a result of dex cool. Mixing the two will cause lots of sludge but it seems you had it flushed soon enough. Even dex cool alone over a decade will cause some sludge from being exposed to air. If that little bit is all you saw I wouldn't be worried. If it doesn't overheat, and if you add coolant and it doesn't drop I wouldn't be worried about the intake either.

There was a lot more sludge when I first removed the radiator cap; the entire inner metal "cup" on the underside of the cap was filled with it, and then some. I do check the coolant level regularly, and it seems to be holding steady now--I did have to add more this past winter, but that was one of the longest, coldest, and most brutal winters we've had in a LONG time. My power steering was also leaking pretty badly then, but it's mostly fixed itself now (I think the PS cap is leaking) I'm sure having to start my car in sub-zero temperatures and letting it warm up for 15+ minutes on at least a half-dozen occasions didn't help, either (I park outside).

It's never overheated, but if I'm idling with the A/C off, the temp gauge will slowly drift from ~185F (1/4 mark; where it normally is) all the way to 210F (1/2 mark), and then go back down slightly. If I start moving again and/or I turn the A/C on, the temp gauge will go back to ~185F. I've noticed this ever since I got the car 2 years ago; is this normal?

I would keep an eye on those strut mounts. That's a lot of rust.

Not nearly as much rust as the underside of my car. One of my parking brake cables broke because of all the rust under there, and there's an actual rust hole under the left rear door (due to a salt truck going by me the other way last winter, and not being able to wash my car for 1-2 weeks afterwards). But compared to most of the other '97-03 Grand Prixs and Buick Centuregals I see around here, my car isn't that bad.

Being a 3100, I would automatically say yes on the intake gaskets. They are maybe a bit more common than the 3800. Make sure you get the metal frame gaskets. And.. keep the pushrods in order, they are different sizes between exhaust and intake.

If only I had the time and money... I'll probably wait until I notice things getting dramatically worse. I do check all the fluids regularly just in case.

Thanks for the quick replies!

 

[Bigjoe980]

Good god, I WISH mine would cool down when I turned the A/C on.

 

[Teraforce88]

When I turn the A/C on mine, the radiator fans automatically turn on and stay on until I shut the A/C off, which keeps it cool. With the A/C off, the radiator fans don't turn on until the 210F mark...

 

[02NavyBlue]

It's never overheated, but if I'm idling with the A/C off, the temp gauge will slowly drift from ~185F (1/4 mark; where it normally is) all the way to 210F (1/2 mark), and then go back down slightly. If I start moving again and/or I turn the A/C on, the temp gauge will go back to ~185F. I've noticed this ever since I got the car 2 years ago; is this normal?

Yes and no. It is normal because many will do this in traffic and 212 is where the fans come on. No because many systems in good shape won;t reach that temp. But that's still nothing to be worried about, 210 isn't that hot.