I have a 1991 240SE wagon. While drive around town with the AC on I overheat. What is going on?
John

First do you have a temp comp board still in the car? If yes, do a search and seek and destroy. First thing you do when you start having sudden overheating issues.

2nd What Stick and V70 said, clean your coils and make sure your system is clean and flowing.

And since you are in FL you may just need look at getting a "SWAMP COOLER", AKA the Tropical Fan Clutch to help push some more air over those coils. That is a Swedish fan clutch in front of that red block and lets just say they did not have that Gulf Coast heat and humidity in mind when they stuck that in there. You can read up on them, I just installed one to help out the AC at slower speeds this year. You can feel a large difference in the amount of air being pushed out. Got the one for my 86 from Dave Barton for less than $100. For anyone south of I10 on the Gulf Coast this is a nice upgrade in over all cooling performance for both the water temp and the AC performance. I give it two greasy thumbs way up.

Good Luck,

Paul

Most likely, your radiator is in need of service. If it's the original rad, it's probably replacement time after 17 years. What you might try first, though, is to remove the radiator from the car and with nothing more powerful than a garden hose, blast out all the crud trapped in the cooling fins from back to forward. You really do have to take the rad out to do a good job of it - too much area is obscured if it's still in the car. You'll probably be surprised to see the amount of stuff that comes out. Take this opportunity to put in a fresh thermostat and gasket, and check the condition of all the hoses, including those little ones at the back of the engine that connect at the firewall.

When you reinstall the radiator, refill the system first with tap water (and make sure there's water in the block before you put the 'stat back in). Run it for a while and see if your overheating symptoms persist. If they do, then it really is new radiator time, and an OEM style is available for a reasonable price at fcpgroton. (I'm out in the AZ desert and that rad is just fine, even in the worst summer heat and in traffic.)




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No one ever went broke underestimating the taste of the American public - H.L. Mencken

Does the 91 have the auxillary fan in front of the condensor? Check to see if it's coming on. Back flush the radiator and the condensor from the engine side. The condensor is a heat exchanger, and it is adding preheated air to the radiator. Follow all the other suggestions as to the coolant and hoses. You may find the problem to be with several of the items.
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Those who beat their swords into plowshares will surely plow for those who did not.

This could be caused by several issues. Have you flushed the coolant and replaced with fresh antifreeze and distilled water? Any evidence the radiator is partly plugged? Are your hoses fresh and not collapsing? Thermostat opening at the right time (when did you last replace it?)? Smashed bugs and debris on the radiator? Radiator cap maintaining the right pressure? Good luck tracing the problem.