Well, this is new. Over the past couple of days my 85' 400i over heats when driving in stop and go traffic. Around a month ago I flushed the cooling system. The oil temp stays at around 100 to 105 C with the water at the same temp. Then when I get stuck in traffic the water temp shoots up to 120+. The fans are running and all seems normal. Any thoughts? Is this 'normal'? Anybody have this problem?
Here are a few thoughts: Thermostat is not opening fully. Water pump impeller is warn and not pushing the coolant water as it should. Radiator has a few plugged veins so not getting the full cooling. Radiator is dirty, thus air flow is reduced. Radiator was not bled completely of air and it is not allowing water to flow correctly. I would start with making sure the radiator is clean and the fins are open. Next I would check to be sure the system was bled completely and there is no air. Check for proper fluid level (when cold). If the problem still remains, you may need to remove the thermostat and make sure it is opening fully when hot. You can do this by suspending the thermostat in a pan of water and heating on the stove. It should fully open before the water boils. You may want to put in a lower temperature thermostat as well.
My first guess is the thermostat not opening and closing properly. Perhaps a more appropriate temperature rating on your thermostat for your particular climate might help. My second guess is that when you flushed your system, you left some air in the system which left you with a smaller amount of water. Get the car warmed to operating temperature, and then open the appropriate bleed screws so to remove the trapped air. This is all assuming that your water pump is operating correctly. That is all I can come up with, so good luck!
If the car did not overheat before you flushed the system, the first thing that I would do is make sure that the air truly has been bled properly. Jack up the front end of the car when you're doing this and use the usual bleed points but also loosen the clamp on the top hose to get the very highest point in the system. Good luck John
Thanks for your suggestions. But before I start down the road of diagnostics, is this something that all 400s are prone to? These past two times were the first that I was stuck in traffic. I've heard people with 3xx cars complain about over heating in traffic.
Easy to check the thermostat. Grab the hose between the thermo and the radiator when its overheating. If the hose isn't good and hot...there you go, she isn't opening.
On my 412 there are no bleeding screws, you bleed by filling the radiator, run the car till the thermostat opens while the heater is fully open, shut her off, let her cool down, refill if necessary, and so on...
Thermostat is working. Fans are working. Pump is working. Nothing measured, just visuals. I've been topping it off the past couple of drives. We shall see, what we shall see.
