Thermostat Replace for Overheating Cure? - PeachParts Mercedes-Benz Forum

jkoebel · #1 02-06-2008, 09:51 PM

I have an '83 240D, which is healthy in most regards. Not too much blow-by, valves adjusted, all that. Anyway.

It has recently developed the problem where at highway speed, 70 mph, I can literally see the temperature needle climb and climb and climb. This is a serious problem as I have a long trip to take tomorrow with bikes on the top of my car which only increase the temperature, because they make the engine work harder to maintain speed.

I have a new thermostat to put in. I was wondering if it is feasible to just run with no thermostat? It's 80F in Florida right now, "not getting up to temperature" isn't a problem at all. Or some way I can force the thermostat into "all-through-radiator" mode, all the time?

Ultimately I likely need a coolant exchange and radiator cleaning. I'm afraid to do a citrus flush because most examples I've read of that on here, end with a water-pump replacement, so I want to do a radiator-only cleaning but don't know where to take it for that. Thats another thread, though.

Post ideas I can do by myself in an afternoon to get my car temperature down.

JimmyL · #2 02-06-2008, 10:12 PM

Most common failure part is the thermostat. I would replace that. A working thermostat is going to cool as effectively as no thermostat, and it will be routing the fluid in all the correct directions {which I still don't fully understand}.
If it is your radiator you may not have a good trip.

Skippy · #3 02-06-2008, 10:30 PM

Start with thermostat. Also when you refill the cooling system make sure you end up with 50/50 or close to it. I helped take over a fleet of equipment where probably half of them were running straight coolant or close to it. Overheating was a common issue until we got the coolant mixtures straight.

I don't know if the cooling fan on an '83 240D has a clutch (my '77 does not), but if it does you might want to check it. I chased an overheating problem on a Lincoln Town Car for several weeks before I finally thought to check that, and it ended up being the problem (or most of the problem anyway). Also see if your electric fan comes on when it's supposed to.

If all that is good and it's still overheating, it's probably radiator time.

jkoebel · #4 02-06-2008, 10:32 PM

Does fan make much a difference at highway speed?

Electric fan does not come on ever because my A/C is not currently working for a variety of mysterious reasons.

Skippy · #5 02-06-2008, 10:36 PM

On the Town Car the fan didn't make much difference at highway speed, but the way it was geared the motor only turned 1500 rpm at 60. Since the 240D spins a lot faster at speed, it might make a significant difference.

t walgamuth · #6 02-07-2008, 12:05 AM

The 240s all had no clutch on the fans, AFIK. ( I have had close to a dozen 240s).

You don't wanna run any mercedes without the thermostat, they will overheat when you need them to be cool and run cold when you want them to be hot. Just a very bad idea. They will not cool anywhere near their capacity without the stat. At least half the coolant will circulate right back to the head without ever making it to the radiator.

Tom W

spugeddy · #7 02-07-2008, 08:40 AM

I say replace thermostat (cheap and easy) and some members have posted messages about drilling small holes in the t-stat to allow coolant to always run through wether open or closed position.....

do a search on drilling holes in it...

t walgamuth · #8 02-07-2008, 08:49 AM

Don't drill any holes.

Tom W

Jordan G · #9 02-07-2008, 08:53 AM

I agree...don't drill and just replace it. You said you already have the T-stat in hand, so start simple and go from there.

jkoebel · #10 02-07-2008, 09:05 AM

Will do. I imagine it takes what, an hour?

t walgamuth · #11 02-07-2008, 09:40 AM

Less.

Just be careful taking the little 10 mm bolts out. They may be pretty corroded into the aluminum housing but almost always come out if you are careflul and coax them.

Tom W

tangofox007 · #12 02-07-2008, 10:01 AM

Quote:

Originally Posted by jkoebel

I imagine it takes what, an hour?

Not unless you spend 50 minutes raising the hood.

jkoebel · #13 02-08-2008, 09:15 AM

I sheared off one of the bolts putting it back in, but its the top-right one. I screwed in the other 2 just fine, and went for a drive, and it held together okay.

The old t-stat had one of the two arms holding the spring disc in place, snapped in half and just hanging. No wonder it didn't activate right.

charmalu · #14 03-20-2008, 12:43 PM

I have been having an over heating problem some what. the 80 deg I have now has an arrow on it, and I read that it is to point up when installing. I am changing it to a 75 deg. but it does not have the arrow. It does have a hole in the edge with a fitting with a bee bee in it. Iam wondering if this to be placed with it in the up position?

Charlie ☺

Stevo · #15 03-20-2008, 01:02 PM

Quote:

Originally Posted by charmalu

I have been having an over heating problem some what. the 80 deg I have now has an arrow on it, and I read that it is to point up when installing. I am changing it to a 75 deg. but it does not have the arrow. It does have a hole in the edge with a fitting with a bee bee in it. Iam wondering if this to be placed with it in the up position?

Charlie ☺

I would stick with the proper OEM T stat (80degree) and figure out why your cooling system isn't working right.