Although I dont see it helping appreciably, in your summer climate i would consider at least 10/40wt oil and personally would go 15/50.

You have WAY more 100+ degree days in one summer than most board members on the east coast expirience in a lifetime.

If I lived where you did I'd be "anal" about my AC too......

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Here's an update.

I installed a new aux fan switch yesterday. There didn't seem to be any changes in my temperature.

Recall, I had two "clean bills of cooling system health" from two radiator shops, based on their letting the car run for about 20 min and feeling for fan airflow and squeezing hoses (i.e. they didn't do any tests). It may be my system is fine. Unfortunately, in my memory I was idling hot at a cooler temp. Word to the wise: if your system seems to be doing fine, WRITE DOWN some temp readings under various conditions (heavy traffic, AC on; freeway, etc.). I frankly cannot recall for certain WHAT my system was doing "before."

I have new plugs, so will be taking them out and inspecting. I will do a compression test at that time. I haven't done a block test yet as I've been loathe to spend $50 bucks on a tester. I would like to verify that I don't have any kind of head gasket leaks. Other than that, I may need to go on a 50 mile + drive to see if I'm okay. The car seems to handle 15 plus mile drives in Palm Springs 105F plus heat okay at this point.

TMAllison,

I currently have 10/30. I'll go ahead and put in 10/40 at my next oil change, which aint too far away.

__________________
Love driving my '77 450 SEL!
124,000 miles

couple things you may not have thought of.why should you believe the temp gauge?you spoke of the crusty stuff in the radiator what if this is deposited on the temp sensor for the gauge and also on the 212 switch?did changing the thermostat help any?i have seen those old stats only partially open.the only things that water pumps do wrong is to leak i have never seen one that did not pump.if the fan clutch is not locking up it will have an idle issue not high speed.it is possible that the aux fan is running backwards and cancelling the airflow accross the radiator.the aux fan has two sensors [1]at the drier for low speed brought on by the a/c [2] 212 switch as emergency cooling [high speed].the relays for this are in the fuse box and the low speed[a/c] sends the power thru a large resistor to drop the voltage and so the speed.when i owned a 77 450sel in texas it was normal to run 3/4 of temp gauge with a/c on.good luck david poole european performance dallas tx.

David,

Nice little post; some nuggets of good info in there.

Why should I believe my temp gauge? Because its never lied to me before? Actually, I have a non-contact thermometer, but don't know where to "stick it" to accurately measure the temp for comparison purposes.

The "crusty stuff" I mentioned - according to a source I accepted - was hard water mineral deposits from tap water (I now have distilled water along w/ my coolant). I suppose it could have prevented a good connection somewhere else.

Unfortunately, I don't know where the temp sensor for the gauge is, actually. At this point, I would clean grandpa's butt if it would solve my problems!

Did changing my thermostat help any? Sadly, I'm not really sure. I replaced it, but still seemed to run hot. BUT... I did not let the car get over 212F before shutting down. It's possible that the thermostat DID help, but I hadn't properly burped the system. (I've never had a car that gave me a problem over "burping" until this one). I CAN tell you that the car has not gotten hot the way it did that first night. The system has never boiled over; and that night - when the gauge read close to redline - I was able to open the cap w/o so much as a hiss after waiting half an hour.

I will have to try to see the fan come on to know if it is spinning the appropriate direction (I presume it should spin in the same direction as the engine fan?). Until the last several days, I was not using my air at all, and was not the night the car ran hot to start my problems. Generally, the climate control system (believe it or not) keeps the car cool enough that I don't need to turn on the compressor - even in Palm Springs. The air blows cold when I DO turn on the compressor.

At this point, my problem may basically be fixed, and I'm just being paranoid (they ARE out to get me, after all! ). But it seems to me like the car is running about 15 degrees F hotter across the board than it was before this happened.

__________________
Love driving my '77 450 SEL!
124,000 miles

I don't have specific exerience with that gasser, but, my opinion is that such temperatures are normal. The diesels, with the older radiators, will reach 212°F. at idle, after a freeway run, with ambient temperatures in the '90s. I'd be chasing an overheat for sure if I had to suffer 110°F. ambients.

I'll also suggest that the replacement of the thermostat, hoses, and pressure cap had no bearing on the results. I'm guessing that you previously had air in the top of the head and you were successful in removing same on the last cooling system repair.

I don't see any issue with running that engine at 212°F., indefinitely, provided that the system pressure holds and you are running proper coolant.

have similar problem before and its the auxiliary fan,

if its a 2 speed fan, with a/c on, the low speed should run and with high engine temp about 87c the high speed should run.

another source could be the circulation to the heater with leaking condenser, this could be tested by temporarily plugging heater circulation