1985 745t

Brickers:

Recently the weather has begin to warm up here in VT, and I've been having some trouble with my cooling system.

Under normal operating conditions the cooling system stays at around the 11 o'clock mark on the dash temp gauge. This includes flats, small hills, highways, etc. However, when I go to town I go down and up a 20-30 degree slope for app. 3 miles, and on the way up my brick begins to overheat. It doesn't go critical, but it will rise to as high as 1 o'clock on the temp gauge and I have been seeing overflow conditions when I get home and pop the hood (the exp. cap has release excess pressure, and there is coolant all over the tank).

About a week ago I swapped in a new Mann air filter. Could this be responsible? I seated it properly and was careful not to break or shake anything when I removed the filter hosing top, but could I have accidentally screwed something up? I also replaced the fuel filter... any connection?

I should also note something peculiar. This winter I would notice that my exhaust manifold was running red hot after driving this same trip to town. I had thought it was just a result of the boost needed to run the hill and that it wasn't anything to be concerned with. However, is it possible that my car is running lean and heating up, causing the cooling system to be overwhelmed?

If this is the case, why does it only happen on the big hill? I use boost in other situations and don't seem to have this problem, so is there a reason that abig hill would trigger a lean condition? I think I can rule out the knock sensor retarding the engine since it doesn't happen at other times. Could it be the oxygen sensor? Does the AMM play a factor in any of this?

Finally, I should also note that I have a black 75kpa cap on my expansion tank. The current one sold is double this (150kpa), but I'm not sure I want to change up and put that kind of pressure on my radiator (I might when I replace it). Is it possible this cap is too low on the kpa and releases fluid pre-maturely?

Over the past 5 months I have replaced the Catalytic converter, exhaust manifold, FPReg, FPRel, Fuel Filter, Fuel Sender, Fuel Pre-Pump, Air filter, ac and alt belts (couldn't deal with the other two at the time), volt. reg. I have also cleaned and gapped the plugs and run cleaner through the fuel system.

Needless to say, any help would be GREATLY appreciated.

Thanks in advance,
Rick