Car is running hot , Hot, HOT(and it shouldn't).

Subject: 1990 Reatta with 76,000+ miles.

Along with changing the oil (and oil pan), a transmission service and flushing the brake fluid, I also just had a major service on the cooling system (radiator held pressure). Everything checked out OK. Today, running with the a/c on (its a freakin' 94 degrees in L.A.), I noticed the temperature level slowly increase until it got to one bar before red (I was driving a steady 70MPH on a mostly level freeway). I turned off the a/c and turned on the heater and the temperature level went back to 'normal' (high noon on the dial) after 10 minutes.

So...a few questions: Should I assume the next step to troubleshoot is the thermostat? Also, what should be the normal operating temperature? Does the Series I 3800 engine have temperature issues?? I put 62,000 miles on a 2000 Regal GS (Series II 3800) and never had any temperature issues (just headaches involving electrical problems centering around the ABS system).

Thanks for the help.

Depending on what water pump you have, it may be the issue. Some of the water pums I have seen have a plastic impeller. This sometimes breakes loose and causes poor circulation of cooland, with no noise or othe signs.

Did it run hot before the cooling system service was done? Generally they do not have overheating issues except for occasional thermostat, or cooling fan failures which show up in slow moving traffic, but shouldn't be an issue in the conditions you describe.

Bushwack

If circulation were the problem then turning on the heater would not cool it off. Take some simple green in a spray bottle to the coin car wash and clean the condenser and radiator with the soap and high pressure wash.

If you still have trouble and need a good mechanic I know of one not too far from you. He works on my cars all the time. Nothing is a problem. PM me if you need the name and number.

That sounds suspiciously like a bad thermostat (heater bypasses) but would check if really running that hot first. If so I would suggest a Stant Superstat in 180F. I use them in all my computer cars and normally run 179-181 at anything over 35 even at 95F.

Now if you are a Californian (or Texan or from a few other misguided states) you have a front license plate and it is probably blocking some of the grille opening (I had a bra briefly and it did the same thing) which is not a good. Many states will allow you to mount the plate on the passenger side instead. Just a thought.

However my experience over the last couple decades is that the 3800 is really a very cool running engine when in top shape and should not have that problem. IMNSHO it should never be over 1/2 way on a 90-91.

Flushing the cooling system every coupla years is a good thing also.

There has been mention that a service manual shows the thermostat installed backwards.

If it was replaced this could be the cause.

As for the water pump, a possibility (didn't think of that).

It was a 40 minute drive from where I bought the car to its first destination - my mechanic to change the fluids, etc. In those 40 minutes, the car didn't get hot.

I forgot to mention that the car was running very hot when I arrived at my first destination. About 30 minutes later when I turned the ignition back on, the LCD dial was nearing red and then within minutes went back to 'high noon'. With that much time having passed, I thought maybe I have a sensor problem???

But my first hunch is a thermostat. I have seen this scenario a couple times in the past with an 1981 Toyota Celica and an '84 Firebird.

Steve, once I figure out how to PM you, I'll take the name of your mechanic.

I may be completely under thinking this, but possibly the shop didn't purge all the air from the system.

Reading quite high after being stopped for a few minutes and then dropping rapidly when running is common and called a "hot soak". Withough the water pump turning the water in the block heats up quickly. Shouldn't be going that high though.

Seeming to take longer than normal to warm up initially but then just slowly going up past there is a classical sign of a stuck thermostat.