My 89 Bonneville has never overheated, in fact I felt that it was underheating since I had it (if that is a term). Lately the temperature gauge has been higher than normal and the past week it has hit the 260 line and fluctuates around that there. The temperature light goes on and off constantly.

1. I have checked to see about antifreeze and there is no problem there.
2. My personal thought is that I have always needed a thermostat. Could this be affecting the car?
3. I believe that the fan is running.
4. I have never changed the antifreeze. Could this be a problem?

Thanks for any help!

You could be right about your thermostat. It could be stuck closed.

And yes, you should have your coolant flushed regularly. It'* also possible that it has built up sludge over time and is restricting your coolant flow, therefore your overheating problem.

My personal recommendation is to get that coolant drained and flushed, and to put on a new thermostat while you're at it. A new thermostat and gasket is a pretty cheap and easy thing to do. I guarantee that it will do no harm and it is very likely to completely fix your problem.
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Coolant flush and thermostat change. They run hotter as they age.
Also a malfunctioning EGR valve could cause cylinder temps to rise as well as a lean 02 sensor. Do the easy stuff first and see if that solves it.

The radiator should be flushed every 2 years. New thermostats are like $10 and are pretty easy to swap in.

I'd do both of those and then go after the other things if your problem persists.

Yes. Though I'm betting the thermostat is stuck closed.

Also make sure that somebody didn't top it off at some point with Dex instead of plain old glycol. (Your car is old style, uses a 50/50 mix of distilled water and glycol for coolant....but there'* nothing stopping someone from sticking in the rotten "new" stuff and making a mess inside the water jacket.)

If it have never been changed, then it is way over due.

Having dealt with my 89 overcooling when i bought it (thermostat stuck open), and then finding when i replaced the thermostat, that the radiator was just not up to keeping it cool, and it would run at full operating temperature around 225*F. So I did a coolant flush and replaced the radiator. THEN I overheated it the day I put the radiator in because somehow, it all leaked out again, turned out the upper radiator hose went. Same day, nice timing huh?

My suggestion, new upper radiator hose, a LARGER, thicker radiator if you can, and a new thermostat, 180 if you live in a moderate climate.

I've never had a problem with overheating with the stock, base model radiator. It has more than enough surface area to shed the heat from the motor provided the coolant levels are full and everything else is working properly (i.e. thermostat opening, pump turning, and no leaks.)

One random thought... Check the obvious too: Take a look at the front of the radiator to make sure you haven't picked up some trash off the road that is blocking the radiator (I had that happen once, picked up a piece of "bubble" wrap off the road and it ended up plastered across the front of the radiator, blocking the airflow through it.)

Yes the stock rad is fine, I have a trans cooler added in front of it, With the stock trans cooler on the rad disabled and a 180 T-stat, and it never overheats. I would recommend a trans cooler though, help save the life of your tranny. 180 T-stat is also recommended,

Good Evening Everyone!

I wanted to give you all an update on the car!

1. Flushed the Radiator twice. So much ORANGE JUNK (YUK)! I will have to do it two to three more times to get it to original color.
2. Changed Thermostat with gasket!

The overheating has stayed consistent at 180-200(halfway marker). On the highway, it will shoot up to 240-250 range. I still feel that this is way too high since I am use to it regularly staying at the 140 range. I believe that it is partly to do with the thermostat and also that I put 1 part antifreeze and 3 parts water.

What is your assessment? Thanks for all your help! [/b]

Orange junk? That'* not right. Your 89 should have the green antifreeze, NOT dexcool (pink/orange antifreeze). It sounds like someone replaced it with the wrong stuff at one point. Good thinking flushing it twice Also, depending on what kind of antifreeze you got, it might already have been pre-mixed with water. I don't know if that would cause the higher temps, but it might... 240 is still way too high, especially on the highway. You should be around 200-205.