300SE - Low heat. SOLVED!!
 

It turned out to be the monovalve solenoid after all. Put the new one in and the result was dramatic.


Thanks for all your help!!!






I have a '90 300SE. The interior heat works a little, but not very well. It takes a very long time to get the heat, and the air just blows warm, never hot. If I park the car for a few minutes and get back in, the air coming out is significantly hotter, but then it cools back down to lukewarm very quickly.

I've replaced the thermostat with a brand new one from the dealer, so that's not the issue.

Also, the air mainly comes through the defroster and very little through the main vents.

Any ideas?


Thanks,


tinypanzer

Have you checked the monovalve solenoid's diaphragm?

To answer your question, no I haven't checked that.


Where is it located and how difficult is it to check? Any special tools needed like a hand pump or anything?



Thanks!!

A flat head screwdriver and a beer would be fine. :)

Look just to the right of the wiper fluid tank, there's a small deal (monovalve itself) with a dual pin plug. Unscrew the four screws and pull the electronic solenoid out. Check the rubber on the flip side.

I'll go do that in a minute! Thanks for the help.


Should I expect coolant to gush out when I pull out this solenoid?


Thanks,

tp

Nope, maybe a few drops only. :)

You were right, only a tiny amount of coolant was lost. The reason I asked was because I'm at work and didn't feel like stranding myself here if the coolant decided to dump out everywhere.

I noticed two things - The seal between the inner smaller pintle and the larger outer one was deteriorating pretty bad. The seal at the end appeared ok, but definitely old. The wire screen was badly clogged up with scale. Somebody must have put undistilled water in there.

I checked the coil and it seemed strong.

So, I'm going to replace the thing, but I'm wondering if the clogged screen wasn't partly to blame. I cleaned it out pretty good. We'll see. But probably best to just replace it anyway, since the seals aren't great.


Thanks for your help!!


-tp

The diaphragm like item is the one you don't want to go bad (tear/rip) in the summer.
The screen being clean now, ought to make an improvement.

There ya have it. Price is $50 or less, just gotta shop around. FL prolly sells them too.

The dead diaphragm is the big issue, I think the build up you're seeing is just lack of maintenance over the years.

You're not on green coolant are you?

Yes,

I am on green coolant. Without starting a coolant thread, is there a good reason not to be? My experience with the red stuff from my '96 impala SS has left me with the impression that the red stuff is overrated and potentially even damaging. But that was a while ago, the stuff may have changes since then.


What should I be running?


thanks- tp

Dexcool is okay in GM, but don't believe the 100k mileage claims. I drain/flush every other year.

Xerex G05 or the OE MB stuff. Light yellow color, like when you have one too many beers after a night. ;)

M103 is super easy to flush. Block drain is around the No 5 cylinder exhaust port. Check all your hoses, there's quite a few behind the main firewall. Good simple maintenance to keep you on the road and not stuck somewhere.



Verify your coolant temp senders are good in the head, usually the aux fan one is bad. Also, the M103 seems to run slightly higher coolant temps than a Diesel or V8, probably due to the smaller radiator which made no sense to me either.

Anyway, I have a new cooling system in mine and I see 82-97°C depending on the season, nothing higher than that while operating. I also dropped to the 79°C thermo from the 87°C and didn't notice much aside from the fan clutch not coming on all the damned time in the summer...

I have driven the car a few times since it cooled off and in the low 40°F temps the motor got up to 80°C+ easily, so the thermo is fine. Also my Turbo BMWs use the 79°C from the factory.



Probably more than you wanted to know. :)

Actually, that information is useful. Thanks!


At the moment, I am tracking down issues with temp sensors. I will shout back at ya if I get stumped.


Thanks!