Thread: 3800 Normal Operating Temp

Originally Posted by 08 198 Champ

Does this sound normal for a 3800 or should I be concerned? BTW, the upper intake gasket was replaced about 20K miles ago but the LIM is the original from what the service records show. Let me know your thoughts.
I'm a first time poster on this site but have been reading it quite a bit lately. Thanks, Bob

Did the entire plenum get replaced or just the UIM gaskets?

Maybe you know, maybe you don't:
The upper intake manifold ("UIM" a.k.a. plastic plenum) sits on top of a plastic framed gasket. That gasket (the "UIM gasket") seals the plastic plenum against the aluminum lower intake manifold ("LIM"). The lower intake manifold sits on top of the "LIM gaskets". The LIM gaskets seal the aluminum lower intake manifold against the engine block and the side of both cylinder heads.

New UIM gaskets help, but the plastic plenum doesn't hold up well to dexcool that has had prolonged exposure to un-metered air. Un-metered air can be sucked into the intake through the brittle/cracked plastic. If the plenum cracks there are two coolant ports right next to the EGR stovepipe that could dump enough water into your engine to completely destroy it; quickly or very slowly. Depends upon the severity of the cracks in the plenum. The wise replacement for the plenum includes a reduced diameter EGR stovepipe that doesn't make contact with the plastic, so hot exhaust gases can be shot back into the intake without dumping all their heat into the plastic.

Significantly trashed LIM gaskets may allow un-metered air, coolant, and oil to enter the cylinders.

When un-metered air enters the engine it can rob the engine of gasoline, which lubricates the upper portions of the cylinder bores. Less lubrication means more heat. All of the above contributed to my modest engine over-heating problems.

Just take a look, I caught mine before any major damage was done.
http://www.grandprixforums.net/lim-g...tml#post588679

Originally Posted by 08 198 Champ

Hi,

I just bought an 03 GP GT with 109K on it with the non supercharged 3800. The previous owner has all service records and really took good care of the care. I see this past fall the coolant was flushed, a new T-stat was installed and the system was pressure checked. I question though the coolant temp as shown by the gage. It looks like the T-stat doesn't open until the gage shows anywhere between 220-230. The temp drops down to one tick above 210 which I assume is 215 and will stay there for a couple minutes then jump back up to 220-225. Then it comes back down to 215 and does this back and forth for 10-15 minutes.

I have a 25 mile commute to work and I notice when I come back into town at a stoplight the temp will drop down to 210 then go back to 220 or so. For the most part, it stays at 220. Keep in mind I'm in WI and the temp here was 5 degrees F this morning. It acts the same way when its 40 degrees to.

I've checked the coolant and it is full and clean, the oil has no trace of antifreeze in it, I see no leaks, and I tried to bleed the cooling system with the bleeder on t stat housing. When bleeding, the engine was at temp, the t stat was open and the rad. cap was on. I tried it twice but got no bubbles. I still think there could be air trapped somewhere. I've also replaced the rad. cap. The heater works awesome also.

I talked to a guy at work today with a Bonneville that acts pretty similar. Does this sound normal for a 3800 or should I be concerned? BTW, the upper intake gasket was replaced about 20K miles ago but the LIM is the original from what the service records show. Let me know your thoughts.

I'm a first time poster on this site but have been reading it quite a bit lately.

Thanks, Bob

Just wanted to give an update. A guy I work with was a mechanic for 14 years at a local GM dealer and replaced the upper, the lowers, the elbows and the orings for me for $300. He said we caught it in time but they were starting to seep coolant into the oil. Not enough for concern yet, but its a good thing we did it now. I've driven it about 100 miles now and everything is dry and it looks like he did a great job. Still have the issue though with it reading warm on the temp gage. The woman I bought it from has service records that say the coolant and the thermostat were replaced this past October - about 1500 miles ago. Also at that time, the temp sensor was replaced. Even though the T-stat is only a couple months old, I still might replace it just for peace of mind if nothing else. The guy who did the work has a scanner he'll let me use to verify if its a gage issue or not. If its not, I'm running out of ideas. This guy was well versed with how tough it is to remove all the air out of the coolant system but he assured me he bled it correctly. Still confused why the temp is still high. More digging to do. Anything else I should be checking?

How about the water circulating pump? I didn't see mention of this anywhere. that could cause higher than normal temps and a "bouncing" temp guage.

One more thing, Spark plugs, are you running colder than normal plugs/gap? Have they been replaced recently? Cold or inproperly gapped plugs can have an affect on engine temps.
A simple check for air entering the coolant system, open the radiator cap, start the motor, watch the coolant flow past, it should be a staedy flow with no air bubbles present.

I borrowed the scanner from the guy who replaced the intake gaskets for me and although the temp gage went up to 3 ticks above half and then settled down, the scanner read 204 degrees. This was at highway speed as I left work. After a couple miles, the gage settled down at 1 tick above 210 and the scanner read only 203. It stayed at 203 for my 25 mile commute. Once I got back into town and stop and go traffic, I did see a 208 on the scanner but the gage didn't move. After I got moving again, the scanner went down to 205 and stayed there. I'm happy (and relieved) to report the gage is inaccurate and the engine is cooling fine.

Now, is there a way to reprogram the stock gage or not? If not, no big deal just curious I guess.

Thanks, Bob