Squeeze the upper radiator hose after the car has cooled down over night. It should not be holding pressure. Have you cleaned the outside of the condenser? The air has to flow through it to reach the radiator.

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

The cap does not release due to heat, it releases due to pressure.
The pressure could be due to heat.
The pressure could be a failed head gasket.

__________________
Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

The highest temperature with the infrared gun is 94C. The dash gauge is reading 110C.

Clearly, either the sending unit (most likely) or the gauge is in error by a serious amount.

Sure, it's "that hot" being 94C. But, it's nowhere near 110C.

You don't have any head gasket issues.

For the cost it would certainly be worth trying a new temperature sender.

Is it possible for a temperature sender to work correctly up to a certain temperature 80°C for example and then send an inaccurate signal as the temperature of the engine rises?

Hooverfull can you repeat the scans with the IR gun when the gauge in the car reads 80-85°C or whatever the gauge reads during normal conditions?

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

OK, sorry for being out of touch for so long, but this, by no means is the problem solved.

To recap.

The car overheats on hills. Used to be it got hot on long freeway hills, but now it would just overheat just driving uphill on any load.

I have replaced:

Thermostat
Radiator Cap
Radiator
Coolant 50/50 mix
Fan Clutch
Fan
Shrouding
Water pump

I have not replaced the temp sender, but it seems to work since it seems to know when the car is going uphill. I do think the needle on the guage is a little jumpy. Also, the car has actually overheated, blown out of the cap when the temp was high.

Other than the overheating issue, the car runs very well.

People have mentioned the head, and I am starting to believe them.

Any ideas?

Did you read posts #23 and #24?

Did you understand them?

Without any more data, we have no confirmation that you even have an overheating problem.

The highest posted temperature with the IR gun is 94C.

There is no problem with anything other than the driver, and, possibly the sending unit.

Ignore these "people". They are usually factually incorrect.

check the resistance of the temp sender when the engine is at 100, and the surrounding area besides the sensor actually reads 100C on the infrared, There is a spec of it on this forum and they can go out of sync, and our temp gauges are nearly "actual" temp gauges unlike new japanese cars whose temp gauge serves purpose of an idiot light.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Heating to nearly-dangerous temperatures only during long uphill grades was one of the only two behaviors my 300SDL exhibited when the head was cracked.

The other was that the system held pressure overnight. You'd drive for a while, get everything hot and pressurized, park in the evening, and the next morning when it should have been stone cold, the hoses were still hard and when you opened the pressure cap, you got a very noticeable hiss as the pressure escaped.

That's an easy test to do. If it happens, head gasket and/or head is a more likely suspect.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

You're not alone. AFAIK Steve/swogee is on year 8 of the same problem - 1987 300TDT Overheats on long hills

Sixto
87 300D^2

Do you have a 1.4 bar (140 marking) cap on the reservoir? How would you see it overflow? A hose goes from the neck to a bottle in the fender.

The aux fan trigger switch on the 124.133 is rated for 105*C. It's the 3-pin switch atop the turret to which the upper radiator hose attaches. I forget which pin pair to jump to test the aux fan. It won't hurt to jump pin pairs to test the fan. One pair triggers the fan (105*C), another pair cuts the compressor (IIRC 127*C in a 124.133, say what???), the third pair does nothing. An 86-87 switch has a lower AC cutout (120*C?), an early 300E switch has a lower still AC cutout (115*C) and a 190D (red top) switch is the lowest I've found rated at something like 95/110*C. Yes, the 190D switch has a lower aux fan trigger which helps cabin cooling on hot days. And when the temp gauge reads 110*C, I won't need AC since I'm not going to drive the car further.

Sixto
87 300D^2

This may be a little off the topic - all MB's in that era came with belly encapsulation panels. With the encapsulation panels on, the main air exit in the engine compartment is through the big air dam in the panel right below the cooling fan. Which way the engine compartment cools better - with the encapsulation panels on or without?

Tan

'91 300D 2.5t
'87 300TDT

I'm also having the same issue. My system does hold pressure overnight, however there is no water in the oil or exhaust in the water, no white smoke during startup or missing coolant. I took it to my mechanic and he tested for the presence of hydrocarbons in the coolant and there was none.

Hey, OP have you bypassed the EGR valve?