Remedying a warm 300D Before Atlanta Summer
 

Hey all,

I've been daily driving my '85 300D for a few months now after a bunch of work done.

Lately, I've been noticing the engine temp creeping up over 100* when sitting in Atlanta traffic. When the car is moving, temps stay right where they should around 80-90*.

I have deleted the monovalve and aux pump with the Klima Design Works kit (highly recommended, I'll do a review later), replaced the coolant reservoir, replaced the thermostat. I did not 'burp' the coolant after the most recent drain and refill, not sure if air in the system can work its way out or if that would be a factor here.

When the temps creep up, blasting the cabin heat does in fact help keep the temps from climbing much higher. Unfortunately, this is a terrible option when the outside temps are hitting 90-100*F+

I did notice a tiny tiny pin hole at the upper hose neck of the original radiator. I have a replacement BEHR to go in but hadn't swapped yet as there hadn't been a need. Guess I'll be doing that now.

I am unable to get out of the car to check if the AUX fan is spinning when the engine temps are climbing and have yet to reproduce it in my driveway. I'm an idiot when it comes to testing electricals but I do have a multi-meter. Any thoughts as to how I can test my fan or its connections? I'm thinking I'll oven/hot water test the new(installed) thermostat when I drain the coolant and swap the rad. Any other thoughts?

Update:

I have tested my thermostat in a pot of boiling water and confirmed that it does open and close properly. Now, if only I can remember whether or not I had it in the housing backwards to start :rolleyes:

I pulled the OEM radiator and went to drop in the new Behr (made in South Africa, fyi) only to find that it's the wrong damn part. In my garage for nearly a year and I'm just now realizing. Has a spot for a radiator cap and no expansion tank/reservoir. Not sure if it's for an N/A model but it does have a W123 PN. Anyone have a correct unit they'd like to trade??

For the time being I flushed the original rad and tried my best to clean out the fins. I'll score the plastic around the upper hose neck and try to patch it with some liquid steel for the time being.

Old: https://www.dropbox.com/s/duh3914alrl6l34/20180317_182432_HDR.jpg?dl=0

New: https://www.dropbox.com/s/vqmfiav2dd0mird/20180317_182439_HDR.jpg?dl=0

Unless the '85 model is different than previous year models, the aux fan runs on the basis of A/C refrigerant temperature.

Probably a dumb question, but would that mean that it would only turn on if the AC compressor is engaged?


Another dumb question: I flushed the original radiator out of the car and stupidly left the nipples for the trans cooler uncovered allowing water in. I just had the trans rebuilt, definitely not willing to risk that $3k job over a $200 rad. Could I flush the trans cooler with some DEXIII before hooking the part back up while I wait for the new unit?

My money’s on a tired fan clutch.

Sixto
98 E329s sedan and wagon

This isn't a bad idea. My fan does turn with ease by hand, what would I be looking for to tell if that's the case?

Fan clutches are cheap and easy, and with 300k+ on the car I think I'll go ahead and just do it anyway since I haven't in the 50k I've owned the car.

''''I did notice a tiny tiny pin hole at the upper hose neck of the original radiator. I have a replacement BEHR to go in but hadn't swapped yet as there hadn't been a need. Guess I'll be doing that now.''''
Did you do that ?
if you have a leak then your water is boiling at 212 F.
it has to be actually under pressure to not do that..
I assume you did do that...

The problem with buying a new fan clutch.... as pointed out in the FSM
is that they are supposed to always be stored IN THEIR WORKING POSITION...
at the parts house, etc...
so it is sure possible to get a new one which is not performing as it should..

The compressor would have to be on long enough for the refrigerant temp to reach the point needed to trigger the fan switch. (The fan will continue to operate if the compressor is switched off, provided the refrigerant is hot enough.)

I'll answer your question then ask my own to make sure I'm following:

I went to replace the radiator this afternoon, only to find out that the new unit I've had sitting on my shelf is the incorrect part. Not compatible with my car.

For the time being, I scoured the surface around the pinhole and covered around the neck with some JB Weld. I have no idea if this is even a worthwhile patch as I have not installed the radiator back because I was stupid and got water into the trans cooler on bottom. So, it's draining as best it can now but I'm not too keen on putting it back in at all. Like I said, $200 radiator and an hour to R&R is not worth skimping on compared to a pricey trans rebuild (which I just had done).

I've already contacted the vendor about getting another new unit, hopefully they're friendly.

Now, to make sure I'm following you: The coolant should or should not be boiling here? There's definitely a vacuum in place as even after 30 minutes sitting cold there is a pretty moderate pressure release when I open the reservoir cap (carefully, of course!) and the coolant level rises in the tank. The pin hole was only noticed today and I have not been leaking a noticeable amount of coolant, so I'm not sure if that's an issue there or not.

Your point on the fan clutches is interesting... There really aren't any moving parts on it uninstalled from the fan, are there? Just the one bearing? (I don't have mine in front of me so I'm looking in my head for it)

The compressor would have to be on long enough for the refrigerant temp to reach the point needed to trigger the fan switch. (The fan will continue to operate if the compressor is switched off, provided the refrigerant is hot enough.)

That's no major issue. I would stand the radiator on end and let it drain overnight, then blow some low pressure air through to dry out the cooler.

I see. So assuming the ambient temp isn't requisite of using the AC (just cool air blowing has been sufficient so far this year) then the engine shouldn't have any need to use the aux fan... Am I thinking this correctly? Furthermore, there would be no signal for the fan to ever turn on without the AC compressor engaging, right? Does anyone ever bypass and add in a manual on/off switch for it?

If that's the case, then I'd definitely have something wrong as I can't imagine I should be dealing with escalating temps when we're still in windows-down weather.

BTW, tangofox, leathermang, and sixto: you guys are always super helpful when I come into brain farts and have dumb questions here. Thanks a ton for being around the site and willing to share your knowledge. Makes me feel not too terrible to work on my own vehicles.

It's clear to me that the aux fan was intended to benefit the A/C condenser, not the radiator.

I drive an '82 300D in Augusta. I haven't seen a coolant temp over 85º C since last August. Under the most adverse summer conditions, I never see much over 95º. A serious uphill grade on a 102ºF humid day might approach 100º C.

Textbook failing fan clutch.