So for the past month or two my 95 Bonne SSE has been running at a very high temperature. Sometimes 250 or so which is pushing the red zone badly. I replaced the thermo with a 195 and just yesterday replaced the water pump and temperature sending unit because my fans weren't coming on by themselves.

After all this it'* still doing the same thing and I don't know what else there is.. It didn't do this the first month or so I had it. I bought it about 3 months ago.

The engine has been replaced with another just like the stock. V6 3800 etc..

Any thoughts? Has this happened to anyone else?

Seems like you need to burp her.

Remove the upper radiator hose from the elbow.
Remove the elbow from the lower intake manifold.
Remove the thermostat
Put the elbow and upper hose back on and top off while the engine is running.
Leave the radiator cap off. It won't hurt anything even if its hot. It'* the removal of the cap while its hot is the bad part.
Watch the coolant level in the radiator while its running. Add as necessary.

Allow to cool off, remove upper elbow(can be done with hose on) Reinstall thermostat, and restart engine.

Let us know how it goes.

You don't necessarily tell us when it'* getting hot, but you hint at the fans not working. Have you checked the relays and or made sure the fuses supplying them are good?

If the engine is over heating, the thermostat is most likely not the problem. I would check to ensure the coolant is moving. I would suspect a clogged radiator. But first make sure like stated above, your not vapor locked.

At the moment my computer is being checked into, because my good friend and the current mechanic working on my car thinks the engine may be a '97 or something like that. He tried to retrieve codes as well since my check engine light is on and couldn't do it. It'* thought that I may have a faulty computer or I have a computer for a 95 and a 97 engine etc..

So my engine serial number is being checked into and a manual thermostat will be inserted into the engine to make sure that the engine is actually getting as hot as the gauge says it is..

The fans are working, but it'* also suspected that the high speed isn't working and when it gets up to say 230 or so when the high speed is supposed to kick in, it'* still running on low speed.

I'll mention vapor lock and see what is thought. I really appreciate the help guys... seriously


And to answer Bill'* comment, it'* getting hot during normal driving. All the time. It takes maybe 2 or so miles to get up to 240 degrees

A faulty thermostat would not let coolant enter the engine block

My coolant is also pretty clear so I thought a clogged radiator isn't likely. But I'll also mention that.

Is your A/C working? If it is, this should help you diagnose the issue. With the A/C compressor engaged, the computer commands the fans to power on high . I am sure you can see where I am going with this.

Also, does your friend have the equipment to scan the codes from GM'* lovely OBD 1.5 system? Bear in mind this system has an OBD II plug, but shoots out OBD I codes. If the scanner is not equipped for this, the scanner will not connect to the computer.

The engine compatibility issue is not really a concern either. There may be some different sensors used, however if this is the issue, and the appropriate sensors not swapped over, the computer will either report it as a trouble code, or run the engine badly, as it is getting data it doesn't know what to do with, but it will still connect to a scanner regardless. The engine itself is exactly the same.

They may be right, the computer may be bad, but replacing the computer is generally regarded as a last resort. I will admit however that PCM'* from the 94-95 work great, when they work, and have been known to expire a little more readily than some hope they would.

Eh, kind of. Though the 95'* have the OBDII plug, it'* more like OBD1.5. The system does have OBDII codes, but not as expanded as the current OBD2 system. 95 was the testing year to graduate to the OBDII system. Only 1 or 2 scan tools that I know of will scan a 95 system. Besided the high end dealer equipment.

Your car could have an engine from any platform from any year between 1995 and 1999? As long as its a Series II and the donor engine got ALL the 1995 sensors.

If your engine was replaced recently, even with a different year, and if all the sensors were swapped from the 95, it'* unlikely the engine is the culprit.

I'm now beginning to wonder if something wasn't connected properly during the swap. Check and verify ALL connections in the engine bay. You shouldn't find a single connector not connected except for the fuel pump test port next to the battery.

As I have already mentioned, try removing the thermostat, reinstall the upper hose and let it run while watching/filling the radiator. Then we can move onto the codes.

I'm totally with Mike on the reason for code retrieval issues. It'* because you have a 95 and likely the scanner isn't cross system, goofy 95 friendly.

Sounds like either your rad is clogged or you have an air bubble. Sometimes it'* necessary to pull the thermostat housing and fill up tot he bottom of the hole before putting the stat in. Maybe jack up the front of the car etc.

As for fans etc. The other thing that is possible is the pcm. Darn 94/95'* can do anything and you'll pull all your hair out before replacing a pcm to find it'* messed up.

Well this guy has worked for pontiac for years and I didn't even have to mention the funny 95 OBD 1.5 system, since he already knew about it, and still couldn't retrieve codes he thought it could be a faulty computer.

I have some random electrical problem too, and the transmission will randomly bog down when its coldish (when I push the gas the engine revs to 3k rpm or so and I won't be moving at the appropriate speed) and sometimes when I switch from reverse to drive the car almost stalls.

I thought the same thing, that maybe something like the chassis ground didn't get hooked up properly.. but I'm sure you all know how troublesome it can be to have to check ALL connections.. I've done an engine swap myself before but it was on a 92 camaro.. this 95 bonne is a bit more complicated.


The A/C works great and the fans do run when its on.. and when the A/C is on it still does get hot. Though if the sending unit for the high speed was faulty, don't you think it could still be the high speed fans?

Also, Mike the water pump was just replaced a couple days ago and everything was flowing nicely.


It'* hard to know if the PCM is the problem when I can't retrieve codes..

I've got a buddy that worked for a Pontiac dealer at the time of these cars as well. These guys saw so many faulty pcm'* that they are commonly whipping that out there as the reason for anything. Which is bad, because yeah it'* a flaky pcm....but it wouldn't cause low tire pressure...lol Just kidding around there.