So I got my handy Fluke infrared temperature gun. I ran the car on the freeway again and replicated the problem. When it was hot, about 110. I pulled the car over and took some temperature readings. Auxilary fan was not running. Here are the readings in Celcius.

Upper coolant hose: 72.222
Lower coolant hose: 58.8
Radiator reservoir cap: 62
Cylinder 1 head: 82.2
Cylinder 3 head: 94.4
On radiator: 84.4

So, any ideas? Is my temp gauge off? It is important to mention I saw some relief pressure coming from the overflow cap, indicating it is actually that hot.

Will investigate some more, and get the oil analysis before I start dumping money in it. I know this can be characteristic of the 603, but is a bit extreme.

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.

I do understand them. I thought it could be my own paranoia. However, it did blow the cap and all the coolant out last week. My paranoia was confirmed. This prompted me to change out the water pump.

The old water pump seemed ok, temp still goes high on hills, I don't want to test it too much. Any help is appreciated on this. I am stumped.

Hoping the problem is the water pump and the temp sender. I will order the sender tomorrow.

It is noteworthy to mention I use all genuine MB parts

This data is is diametrically opposite to the data that you posted with the IR gun. It cannot blow it's cap and lose coolant unless the coolant boils, and that doesn't occur until the engine reaches 120°C. if the coolant is proper.

Therefore, with conflicting data, nobody can really help you with precision. You'll just get a bunch of WAG's..................

Sorry.