318ti doing its level best to overheat

Since last spring, my BMW 318ti with about 90,000 miles attempts to overheat on hot days and stuck in traffic. As I live in the Metro DC area, this means it occurs a lot. It has never ever made it to the red line - just pops over to about 3/4 of the way on the gauge. Once I start moving again, it does reset.

I have had a new thermostat, new water pump, new hose, and a the coolant drained and replace, and a new fan. Went all fall and winter with it running great, but the first warm day and the sucker tried it again. My mechanic is stumped. Any thoughts?

Is the cooling fan electric or direct drive? If electric, does it operate properly? Is your A/C operating when this problem occurs? That will force the cooling fan to operate. If these things check out, you may need a new radiator as after a while, they get plugged up with mineral deposits…

The only component left that can cause this kind of problem is a partially restricted radiator. If some of the radiator cores are restricted, the radiators capacity to remove heat is reduced. During cooler days, enough cold air passes through the radiator to compensate for this capacity reduction. When the temperature increases or when stuck in traffic, the air isn’t as cold and not enough is passing through the radiator to compensate for this capacity reduction. And the engine starts to overheat.

One way to check for this is, get the engine up to operating temperature. With the engine idling, take an infrared thermal gun and point it at the radiator cores. Those that are restricted will show up much cooler than those that have full coolant flow.


I am not sure. If I ponder it, I think it occurs more if the AC is not running, but will have to think about it.


CLEAN the engine. A coating of all the gradual time accumulated grease/oil/gunk over the outer surfaces of the block ,head and such acts as an insulating blanket. A clean engine can dissipate heat along with the coolant system .
CLEAN the fins of the radiator and a/c condenser for maximum aiflow. Again this is a gradual time issue that most of us overlook.

( a good cleaning was the hidden key factor of my 80 Bronco summer overheating. )

Does that require replacing the whole radiator or can it be cleaned out? And how much money am I looking at as I swear I drop way too much money into this car.


I think your radiator has plastic tanks and aluminum tubes/fins. Those require replacing. I found them for about $160 on the internet, check your local parts stores (not the dealer). That doesn’t include shipping and installing, of course. A radiator shop can flow test your radiator to confirm blockage, but I’ve heard it’s fairly common with older BMWs. What year is yours?

It’s a 1998. I love, love this car but am debating replacing it after 8 years due to the fact I am spending more on repairs then what it’s worth. But if the replacement of a radiator is pretty simple to do and fixes the problem, then it might be worth it.

Thanks for your assistance.

Of all the things to replace, the radiator is one of the simpler items. Just a few nuts, bolts, and clamps (with a drain bucket below), and it’s off.