My 1988 560SEL is overheating. I have combed the past post trying to nail down the problem. Still no answer.

One day while driving for about 15 minutes the temp maxed out and the coolant poured from the over flow. I ran a test on the fan clutch and it failed. So, I put in a new one and it passed. However, it still breaks 120 in about 15 minutes; I pulled the temp sender to fill the engine back with water to insure there were no air pockets. Still it hit 120. I ran the inside heat and it works great especially at 120 engine temp. I checked the thermostat and could not find one. Maybe the previous owner removed it? I assumed it was in the housing that the temp sensor is screwed into??? All my secondary fans are working. When I drive the car it has plenty of power. Just before it reaches 120 I bring it back in to cool down.

What in the world is going on? Is it finally over between us?

Your comments are appreciated.

Engines need a thermostat. It provided resistance to the water flow, thereby creating pressure. This pressure increases the boiling point and also eliminates steam pockets inside the cooling passages.

Put in a thermostat.

http://mb.braingears.com/126_DISC2/program/matrix.htm

http://mb.braingears.com/126_DISC2/program/Engine/107/M117_56/20-110.pdf

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

You do NOT have a thermostat? You are looking in the right place?

Running without a thermostat will definitely and certainly cause the car to overheat in warmer temperatures in this engine. The thermostat (unlike many in US cars) actually performs two functions: the first and obvious is that it opens and allows water to flow through the radiator. However, the second function that happens along with this is that a "bypass" from the engine outlet to the water pump inlet is closed off. This is a "low resistance" path that if left open will "short-circuit" the longer, higher-pressure (resistance) path through the radiator. With no thermostat, you have no bypass function.

That you have heat is not surprising; it comes from the rear of the engine; the temperature sensor is near the outflow from the engine itself. I wonder if your radiator is actually warm.

__________________
86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

Everything is hot and percolating. Meaning the overflow is bubbling and the radiator (1 year old) is hot and all the hose look pretty tight. I am beginning to wonder if the thermostat is actually in the path of the lower radiator hose. It is getting too late to take a look. However, does anyone know where it is supposed to be on my model?

Look at the service manual link I provided earlier.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

That is a great link. Thank you.

It looks like it is on the side. I hope tomorrow I can get it tested and changed if needed. I going to feel pretty foolish if that is all it is. I have been trying to figure this out, waiting for a fan clutch, and getting rides to work for almost two weeks. I will just tell the wife it was the $$$ fan clutch.

Warren knows what he is talking about, looks like it will be sorted out now,
so the relationship with your wife, and with the Mercedes 560 are not over, and hopefully, that is a good thing

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

I found the thermostat on the side of the water pump on the lower radiator hose. I pulled it out and noticed some grains of something around the shaft. So, I boiled the crap out of it on the stove and it never opened. I guess they can fail open or closed. Mine failed closed. I had to order the part so I could not test a new one. However, I put it all back together without the thermostat and it runs at about 60* on an 80* day. Thanks for the help. I am sure all will be fine this summer with the new fan clutch and a thermostat.

Man, I love a Happy Ending!