I just got a 1981 380SE. It has an overheating problem. Temperature climbs all the way to 120. There is no thermostat fitted. Could that lead to overheating?

Also, how to test that the water pump is doing its job without removing it?

Please help!!
Adam

Ignore the thing about missing thermostat - I was looking in the wrong place. I have the version where it's on the side of the pump housing

If you're not low on coolant and the temp gauge can be trusted, I think it's safe to say that if you reach 120C then the pump is not doing its job and you don't need to test it! Replace it before your engine melts!

(I'd use a 2nd thermometer, after it's shut off put it in between some rad fins, to make sure the gauge is right, if it isn't showing any symptoms of overheating such as boiling over)

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

I am not low on cooland and the temp gauge *can* be trusted. When I reach 120 it sounds like under dash relay starts to click. Also there are other sign which make it sound like it's pretty hot. However, I have never had the engine boil over through the expansion tank cap. Or from anywhere else for that matter.

With the top rad hose removed and the engine cold I can see that the waterpump is pumping water around, so it's not as if the water is not flowing.

When the engine is at operating temperature I tried to feel the radiator and the bottom rad hose. Both are quite hot.

I removed the thermostat and tested it (not the first time I've done this operation on an MB). It seems to be working fine too. By the time the water is boiling in a pan the thermostat is fully open.

Why would the waterpump be less efficient than when new? Although I can't think of any other reason right now why the engine isn't being cooled enough.

Incorrect coolant to water ratio will cause it to run hot too. 50/50 is always a good starting point. When I got my 560 the PO was running what appeared to be 100% coolant and had drilled a number of holes in the thermostat rim to help bring the temp down. A new T-stat and 45/55 mix did the trick.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Also - inferior coolant, adding poor quality water, or just never changing it can lead to a ton of rust and deposits in the system.

If the coolant is rusty at all, flush the system really well with MB Citric Acid flush! You can do this with the thermostat out too, and even take it on a little drive while doing it. Make sure to drain the block too though.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

If the thermostat only opens when the water is near boiling, it's bad.

You need to check the temp -- probably should start to open at 80 or 82C, and be fully open by 85C.

A badly clogged radiator will cause the engine to overheat even if the thermostat is good.

I'd use a thermometer and check the temp of the coolant with the radiator cap off to verify the temp -- guages and senders have been known to be wrong!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Following up, the overheating problem was being
caused by the radiator. After I put the flush in, the radiator started
leaking water. So I had to remove it to fix the leak. In the process of
removing it I sheared off the bottom oil cooler nut, ouch!

Once I removed the radiator I found out the reason it was not cooling
properly. The radiator was totally blocked. No air could pass through as
pretty much most of the front had become a gooey mess. It wasn't so much a
question of finding and patching up the leak as replacing the entire core.
However, I needed a new oil cooler too.

So I went to Mercman breakers in Southampton and for £140 got a "new"
radiator and oil cooler. Apparently they are rair. This one has a thicker
core which was a bonus. The main dealer wanted £290+VAT for the radiator
alone. Recoring may not have been possible with this rad as not all Behr
rads can be recored and would have cost £85+VAT.

The car is now running perfectly. Around 80-90 in most conditions.

Thank you all for advice.

Don't you hate the feeling you get when you do something like this.

__________________
Jim