PontiacBonnevilleClub.com

OK, a couple of weeks back I swapped out the thermostat and drained as much of the Dexcool as I could. Topped everything back off and have been driving it everyday for the last two weeks with no incidents other than the day after I did the thermostat I got the low coolant light. I topped the surge tank off again, and then decided to order a new sensor (havent installed it yet) in case it did it again. Today went to the parts house to pick up a part for another vehicle in the GXP. When I left the parts house the temp needle pegged after about a mile or so. I pulled over and checked it, surge tank still had fluid, figured it was just glitching as the fans werent running as if it was hot. Restarted and got back on the road and a few minutes later I got the low coolant light. Needle pegged again. There wasnt anywhere I could stop right away so I decided to stop at my brother's house on the way home. Then it shut the HVAC system down. Right before I got there, the "Change Oil Now" light started coming on between the low coolant flashes. As I pulled into his driveway, the engine started missing and I figured it had kicked into 4 cyl mode. Shut her down and the fans ran on for about 10 minutes before shutting off. Coolant had been blowing out of the surge tank overflow. I'm thinking great, the new thermostat stuck or the water pump is gone at 30k miles.

Let it cool for about an hour, refilled the surge tank with Dexcool, started it up and drove home with no problems, engine stayed at 200F the whole way. Pulled into my drive and let it idle for about 10 minutes, no more problems, it never ran hot again, but the fans werent running even though it showed a steady 200 degrees, what temp do they kick on at?
It threw a code and I checked it with my scanner and I think it was a dealer svc code P1258 which shows it went into protection mode code, I cleared it and started it and let it run for about another 10 minutes with no further issues.

Could it be air in the system, would that cause it to overheat this much? I noticed on the way to the parts store that I could hear it gurgling, like it was coming from the heater core area, today was the first kind of cold day we have had (40's) since I changed the T stat. I remember when I changed it that I couldnt find a bleeder valve on it but figured it would eventually burp the air out. Hence refilling the surge tank....

Thought it may be the head gasket, but no smell of coolant in the exhaust. Havent pulled the plugs yet.

Any ideas or tests I can run before I start throwing parts at it?

Drove it to work this morning, no issues. Stayed at 200F the whole 30 miles. Pick up some brewski's this afternoon and pull it into my shop, gonna clean all the purge lines and throttle body, see if there is an obstruction somewhere. This is crazy.

Sounds like there was just air trapped in it. Are you still having overtemps? 200 degrees sounds about right for the temps. I am not familiar with the N*, but others will chime in eventually.

The temp gauge is actually funny in these, it will read 200 degrees from an actual temp of around 195 up to around 225 or so, Jerry found the same thing with his GXP confirmed with his scanner. These engines do run warm so even 220 isn't a big deal and pretty normal so I would guess that's why they are set up like that.

I would also check the purge line for any blockage. If this random overheating continues though I would really recommend a coolant sniffer test (can't recall the exact name) it checks the coolant for traces of exhaust gasses and is about the most reliable method to confirm or eliminate head gasket issues.

Also, there is no 4 cyl mode on these engines, FWIW...

00Beast wrote:Also, there is no 4 cyl mode on these engines, FWIW...

Yes there is. When they overheat up to a certain temperature they go into a limp mode only running on four cylinders.

There is indeed, but I wouldn't count on it to save the day: http://hollywoodbix.tripod.com/NorthstarEngine.htm

In addition the Northstar Engine features a "limp-home" mode that keeps the engine operating without engine coolant. "Limp-home" allows the engine to continue running by alternately delivering fuel to only four of the eight cylinders. The four remaining cylinders do not fire, but continue to pump air, cooling the engine and allowing you to safely drive at 50 mph up to 50 miles for help.

Northstar normal operating temp is usually anywhere between 200 and 220F. Mine seems to find home right around 210.

repinS wrote:There is indeed, but I wouldn't count on it to save the day: http://hollywoodbix.tripod.com/NorthstarEngine.htm

In addition the Northstar Engine features a "limp-home" mode that keeps the engine operating without engine coolant. "Limp-home" allows the engine to continue running by alternately delivering fuel to only four of the eight cylinders. The four remaining cylinders do not fire, but continue to pump air, cooling the engine and allowing you to safely drive at 50 mph up to 50 miles for help.

Northstar normal operating temp is usually anywhere between 200 and 220F. Mine seems to find home right around 210.

And in about 10 mins they start "clanging" and reach the point of no return shortly thereafter, take it from me I have had four Cadillac's with the Northstar. When the head gasket goes bad they will remain driveable at first and will even be able to take short trips up to about 30 mins, but once they reach full operating temp its all over and the change oil light comes on just because the viscosity monitor is telling it the oil has thinned. However I thought by 2004 the head gasket issue had been resolved (I could be wrong), as it is a different generation Northstar.

97ParkAve wrote:

repinS wrote:There is indeed, but I wouldn't count on it to save the day: http://hollywoodbix.tripod.com/NorthstarEngine.htm

In addition the Northstar Engine features a "limp-home" mode that keeps the engine operating without engine coolant. "Limp-home" allows the engine to continue running by alternately delivering fuel to only four of the eight cylinders. The four remaining cylinders do not fire, but continue to pump air, cooling the engine and allowing you to safely drive at 50 mph up to 50 miles for help.

Northstar normal operating temp is usually anywhere between 200 and 220F. Mine seems to find home right around 210.

And in about 10 mins they start "clanging" and reach the point of no return shortly thereafter, take it from me I have had four Cadillac's with the Northstar. When the head gasket goes bad they will remain driveable at first and will even be able to take short trips up to about 30 mins, but once they reach full operating temp its all over and the change oil light comes on just because the viscosity monitor is telling it the oil has thinned. However I thought by 2004 the head gasket issue had been resolved (I could be wrong), as it is a different generation Northstar.

It seems problems may have been reduced but I don't think the head gasket problem was ever "cured" from the factory. Stud kit seems the only way to repair once they fail.

Its terrible so many beautiful cars have been killed by this, I had a 1996 STS black on black with 60k that was absolutely beautiful that got taken by the Northstar bug, along with a 1998 + 2001 Deville. Thats why I stick to the 3800's now.

97ParkAve wrote:However I thought by 2004 the head gasket issue had been resolved (I could be wrong), as it is a different generation Northstar.

I think the issue was resolved for the most part. Ryan (crash93ssei) had a head gasket failure on his GXP during his brief stint of ownership. It lived a long hard life and had well over 220,000(?) miles on it with an unknown history of maintenance. My best guess on that one is that it likely wouldn't have been a failure from the traditional problem of head bolts stripping/pulling out of the block, but rather a pure gasket failure due to general old age and neglect by the previous owner.

My motor puked a valve spring on the original owner at 75,000 miles, but to date I have NOT heard of a single case where someone had one fail also. It appears to be an anomaly at best.

Its gets driven about 45 minutes one way to work each day down some twisting country roads with a lot of stopping and starting at intersections. The change oil light now has stopped coming on, I read somewhere that after so many normal drive cycles it would reset itself. I just changed the oil in it two weeks ago with Pennzoil synthetic and AC filter. Havent had a problem again since, it has done this twice in the two months I have owned it, the first time it went over 200 but I got to where I was going before it went any further, this last time I pushed it to the limit. I can smell antifreeze occasionally around the engine, but it puked so much out the drain tube it could be residue from the last episode. I am going to pull the plugs and check and see if any of them has signs of antifreeze, also ordered a sniffer test kit, should be here next week. If it is a head gasket dont know what I am gonna do. Stop leak and trade it in, but I doubt it. May do the stud job on it as I like everything else about the car. Just pisses me off that with 30K miles it has these problems.

Still have the initial rough idle when the engine is cold for about 30 seconds. It is not as bad since I started running a bottle of techron at each fill up and tightened up the intake manifold and cleaned the TB, but its still there, I think its a sensor, you can hear something click under the hood and then it runs smooth.

Havent been able to get it into the shop yet to further diagnose as one of my other hanger queens is in there on the operating table right now but will post back if I find anything. Why the crap didnt they put an LS1 into this thing!!!!??

ok, got the Lisle 75500 Combustion Leak Detector in and tested it. Says test it for two minutes letting it draw fumes from the tank. Didnt change color. let it sit on there for about 5 minutes with the engine running and it finally changed to a light green color. Not sure what this means as the directions say it should turn yellow if there is a leak. Also noticed some I had poured in a water bottle and left sitting also turned light green, atmosphere?

Dealer has it right now fixing the door, when it gets back I am gonna pull the plugs and see if there is any evidence there. Local mechanic told me it could be the intake manifold gasket leaking. My bolts were only finger tight before i tightened them down. He had just repaired a Northstar in a caddy where the waterpump and intake gasket had failed. But he did say it was running hot more often than not where mine has only run hot twice in the few months that Ive owned it.

Wow. I'm basically having the exact same problem as you are right now. It's at my mechanic as we speak and he's checking on some things, but his first call was leaning towards a head gasket.