W123 running a bit hot - PeachParts Mercedes-Benz Forum

spdrun · #1 10-11-2014, 02:08 PM

I noticed my 240D was running a bit hot in summer, so I replaced the thermostat with one from NAPA. This was supposed to be rated at 80C, I believe.

What I'm getting:
Idling: about 95C to almost 100C.
Driving: about 90C
Driving over about 75mph: creeps up to 95C
Turning heater on: drops to 80-85C, then creeps back up to 90, guessing as the thermostat chokes down flow through the radiator.

Shutting down the car, then restarting after 5 min: about 105C, dropping to 90C after water starts circulating.

Fan is mechanical, so shouldn't be an issue. Did I just get a dud thermostat that opens too high, or should I be looking twice at the water pump or radiator?

leathermang · #2 10-11-2014, 02:26 PM

First be sure the fins on your radiator AND condenser are straight and clean....
they make ' combs' for straightening them... you can easily lose 10 to 20 percent of your air flow to bent fins....
Did you check to see if you have an air bubble after filling with coolant ?
Some report they need to park the car with the nose up and ' burp' it ....
Do you have new proper coolant in it ?
Do you have new radiator cap... with good sealing and checked for proper pressure opening ?

junqueyardjim · #3 10-11-2014, 02:44 PM

You didn't specify model but I think you have a 240D with a 4 speed. It should be the easiest car in the world to keep running cool, but over the years and miles, things get messed up. Off hand, I would suspect the radiator to be 100 percent of the problem. They can get plugged up both internally and externally. You know it is a pretty simple job to pull and replace that radiator. Simple but kind of messy and you need a place to do it. But that is what I would do, pull that radiator and just clean it out. With a good high pressure water stream really blast the crud out from both sides. If you have air pressure to assist in blowing, so much the better. Could be done in the car, but it's messy and not as effective. Then check the flow of the inside. Hold your hand over the bottom out let and fill the radiator up - release it and see how it comes out. Even with no pressure it should empty in just a second or two. If it doesn't empty fast either the tubes are plugged throughout their length or scale has built up over the top at the bottom of the top tank. Radiator shops can do a good job of boiling them clean in a pretty nasty solution. Sometimes nothing will clean them up and the radiator will need a new core. Sometimes an upper or lower hose will collapse on a bend, but that is pretty obvious. I would take it out, maybe fill it with that common product called CLR which is used to remove the calcium buildup in house hold plumbing, shower heads, ect. Lay the radiator down so that the outlet/inlet face up and fill it with CLR (sold in the household section of supermarket) and water and let it lay for a couple of hours. Then check the flow again and hope for the best. With the radiator out of the car, and all the coolant out, pick it up and view it under sunlight or a good light and you can see how much crud has built up over the years. Dead bugs, old grass, maybe some feathers, some road tar - hey it's a mess in there.

unkl300d · #4 10-11-2014, 03:45 PM

I cautiously submit that CLR may not be compatible with aluminum radiators.

CLR is a great product for its intended purposes, however.

Heavy duty prestone radiator cleaner soaking for a couple of days would be safe in general.

Its your call.

leathermang · #5 10-11-2014, 03:55 PM

For flush directions...
1987 300TDT Cooling System Flush Procedure

Rogviler · #6 10-11-2014, 05:46 PM

My wagon was doing the same thing. It was as simple as undoing the radiator, seeing that the space between it and the condenser was about half-full of leaves and dried mud, and cleaning all that out. Check the simple things first...

-Rog

rocky raccoon · #7 10-11-2014, 06:32 PM

Check your radiator/expansion tank cap. If the seal is old or gone, the system will not pressurize and it will run hotter. Replacing that cap cured my similar issue.

Any 13psi cap will work.

spdrun · #8 10-11-2014, 07:04 PM

Added a bit of coolant and pumped the upper rad hose on a hill -- it seems to be quite a bit better. BTW - is a 240D supposed not to have an expansion tank? It looks like there's just a rubber hose terminating at the bottom of the radiator, draining to the ground.

leathermang · #9 10-11-2014, 08:04 PM

You have a cheap car... it did not come with an expansion tank....

uberwasser · #10 10-11-2014, 08:31 PM

To be fair, none of the non-turbo W123's did. Even the more expensive 300D's

junqueyardjim · #11 10-12-2014, 05:27 PM

Quote:

Originally Posted by leathermang

You have a cheap car... it did not come with an expansion tank....

The above is a very erroneous statement. And no one appreaciates a remark like that. Regardless of the current value or worth of his car, when it was new it was not equipped with a coolant recovery system and it was not a "cheap car". When it was new it was probably more expensive then a well equipped Cadillac Sedan.

leathermang · #12 10-12-2014, 05:42 PM

Did you notice what I own ?

Skippy · #13 10-12-2014, 06:38 PM

Jim, there's this thing called "sarcasm".

Earl.Allen · #14 10-12-2014, 07:44 PM

Quote:

Originally Posted by junqueyardjim

The above is a very erroneous statement. And no one appreaciates a remark like that. Regardless of the current value or worth of his car, when it was new it was not equipped with a coolant recovery system and it was not a "cheap car". When it was new it was probably more expensive then a well equipped Cadillac Sedan.

I don't think it was meant that way. I think his reasoning is like mine - They are cheap cars, I've had several 240Ds and only paid $500 to $2,000 for them and my 300D was several thousand.

mistersooty · #15 10-12-2014, 08:29 PM

If you determine that the radiator is the issue, a radiator from a NA 300D fits nicely.

When I had working Ac it provided me a little bit of insurance especially at full throttle.