Hi all. I need some help. I am in a predicament that is to long to explain so I will just say what is happening with my bonne. I have a 1990 Bonneville sse that is over heating. I have checked what I know. The thermotat is not sticking, water pump is working proper, fan is working proper, no vapor lock, circulation is fine, coolant is not even 1 yr old, no obstructions in rad, basically nothing that would first come to mind is a problem. Still there must be something. Ideas would be greatly appreciated. I am a new member, sorry that I didn't do a personal info or anything. Need to get this problem fixed tonight. Or I will have to take the chance and drive an uninsured charger tomorrow (feeling sick in my stomach over that thought). Thank you.

I know this may sound silly but do you have heat? When did this problem start? Have you tried running it without the thermostat? Sorry, I have more questions than answers at this time.

Sounds like all is well, is the engine getting hotter then hell and locking up? That happened to my Bonneville when I lost my block heater frost plug.

HOWEVER, it could be the gage or the coolant temp sensor.

Any error codes? (ie SES light)

Thank you for replying. Yes I have heat. At first when I started the car, it ran for 10 minutes before I got in it (leaving work) and there was no heat. It usually blows heat after about 5 min. Heat tonight however started after I got going. Then I noticed the overheating problem while driving home. My first thought was vapor lock, but I only added about 1 liter of coolant to the system and still to hot. Yes I even dared to touch the rad hose. Scalding. Didn't burn myself though. When the thermostat, fan kicks in, it does cool down but not enough for safe oporating temps. And yes my check engine light went on over the weekend. But the code is reading tune up. So I suspect just new plugs and wires. Really, I thought of what I posted and all checks out. Now I'm thinking maybe an obstruction within the engine? But if I have good circulation, what gives?

You need to get your codes read to properly diagnose what the problem is. There is a way to do the OBD1 ECM check yourself and you can refer to TechInfo on this site for that info.

But I'm thinking based on what you have written that its a sensor problem. The ECM will shut the car down if it gets to hot, since the cooling system in general is fine, it most probably is the sensor...the Coolant temp sensor can be wonky

Get those codes read and get back to us.

Thanks. Will do. Just came back from a little drive to crappy tire. It must of been a gremlin, but I think that maybe it is the sensor because everything is running fine. Temp was running normal. Picked up a new thermostat and rad cap in case. But now it seems that what has happened was just a warning about the sensor starting to go. Thank you for your help. It looks like this year, instead of putting my dollars into my resto project '74 charger se 400 4bbl stock' I will be wisely investing it in my bonne.

Normally a 3800 is a very cool running engine. What I would do is to leave the radiator cap off from a cold idle and see if the coolant starts moving as the thermostat opens - is very visible.

That said, self healing problems are generally electrical though it might also be a sticking thermostat even if new. Have seen a bad ground foul up a lot of things, does the reading change if you turn the headlamps or turn signal on ?

BTW if the sensor is bad and is telling the ECM the engine is a lot hooter than it is, it will change a number of parameters. Scan tool to see what is really going on helps here