I glance at my temp gauge quite a lot these days. Since I put in a new stat about a year ago it's been running at about 82 no matter what. Added bonus, I've been getting heat on demand from climate control. A buddy of mine sells OEM German and Italian parts and had a monovalve cartridge on the shelf, was not OEM but early after market and by God it worked.

A couple of days ago on the freeway, warmish day - 60 - I noticed I was a tad over 100. I pulled over with it running, nothing out of the ordinary. Slowing to below 60 kept it close to 100 but 70 or more and I was flirting with 105.

I know I've heard they do well running hot but much higher than this and seems like trouble would be had. I found this 2011 post from the long gone Brian Carlton saying the extra heat prolly not a problem.

But this is a bit sudden. Additionally climate control heat vanished at the same time. I want the old temps and the cabin heat back. Seems a large coincidence that climate control went south at the same time. Not sure what an OEM monovalve cartridge runs these days but I'm reluctant to replace spendy parts willy nilly.

Other suggestions on line are water pump and centrifigul fan. None of those explain the sudden cabin heat loss.

The big hope is, of course, someone has had this exact problem before.

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1986 300SDL, 362K
1984 300D, 138K

Did something happen to Brian Carlton?

I'm sorry, I meant long gone from the forum owe to untimely banning. We had dinner about a year and a half ago on a trip he made to the Bay Area. Went to a boisterous tavern and burger joint when they were still boisterous.

He's still doing well AFAIK.

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1986 300SDL, 362K
1984 300D, 138K

Thanks; did not mean to hijack your thread. I liked him and valued his advice.

Check your coolant level. Seems like a stupid suggestion, but if you have a leak and you're low, you can be running high temps. Low coolant level would also delete your cabin heat.

Check for pressurized cooling system. Cracked head or blown head gasket can dump combustion gas in the cooling system and cause high temps and poor water circulation.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I checked coolant levels, a tad low. Adding made no difference.

I looked at an ongoing drama with me. the uneven idler pulley on the serpentine belt. It had been leaning a bit, all of a sudden I saw on that day that it was leaning a lot and the belt looked like it was distorting going over the pulley. Only a small chance that it was the issue slipping on the water pump - but I thought finally I must address this thing just in case and on general principal. I really wanted an overhaul so I removed the radiator. The bolt on the rocker was way loose - dumb, doesn't help the outer threads any. I took it out, WD-40ed the hell out of in and out followed by brake cleaner and air. Put in a fair amount of blue loctite (no red on hand) and tightened that sucker good.

Not the problem. But good to get off my back. And coolant was added deluxe. Now I just need to get this other problem resolved or it was all in vain. This is a why I don't just like guessing and replacing parts.

No signs of head gasket or block issues but I'll investigate.

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1986 300SDL, 362K
1984 300D, 138K

Sounds like your heater core has lost circulation. A crack in the head can form an air bubble that impacts circulation. Just something to keep in mind.

If it seems to be nothing simple You might want to get a test kit for the presence of hydrocarbons in the coolant. Fortunatly there is an easier test. If the rad hose is hard next morning you have the probable answer. Seems to be a fairly reliable test if the coolant system is tight.

I agree. He could be imperious but so can I. His advice and knowledge was much valued. It was neat meeting him. He had a late model small Mercedes rental and was showing off the massive braking power. It also shuts off at stoplights and starts when you release the brake, or something like that. New one on me.

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1986 300SDL, 362K
1984 300D, 138K

Good tips. To add to the fun and games an hour ago I noticed an abundance of white smoke exiting the pipes. No overheating. Oil looks normal, level unchanged. Coolant likewise.

Who knows, at some point I might have to admit that this car won't live forever. I found this great thread from 2011 about an SDL smoking bad. Had some old the old names we don't see any more:

http://www.peachparts.com/shopforum/diesel-discussion/344243-please-any-help-tough-smoke-problem-300sdl.html

*EDIT*

Went out just now, several hours after driving, and the upper rad house sure does seem to have some pressure going on. Are you saying that might indicate either a cracked head or perhaps instead a blown head gasket? I can guess as to which would cost more to fix.

More edit, it just occurred to me that this cooling system will stay pressurized for a long time, just from normal driving.

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1986 300SDL, 362K
1984 300D, 138K

Definitely do the test, rent the block tester at autozone and purchase fluid at harbor freight.
Other test: pressure kit for cooling system from amazon, buy, test, return. It should keep about 11-12psi over 15min at the very least. You will also immediately see which hoses to tighten.

You can add an UV dye to your cooling system before the pressure test, then look at everything with the lamp.

I've done all of this, but my increase was from 82 to 90 after complete cooling system overhaul. And yes, 90 is well within spec, but I wanted to triple check my job.

Good luck

In all the searching on this, Bars Leak keeps telling me their product will do the trick.

I'm leaning towards head gasket more and more. The 'smoke' had no smell, didn't really have a smokey feel.

You have to wonder about Bars Leak. Selling a spendy product to desperate people that, who knows, has a 10 or 20% chance of getting you down the road a few more miles. This guy is not big on Bars Leak. Makes sense:

https://www.youtube.com/watch?v=FQMlOAiSql0

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1986 300SDL, 362K
1984 300D, 138K

You can just put compressed air into the cylinder when a piston is at tdc on compression stroke and watch the coolant reservoir.

That will clear up any doubts you have about the cylinder head or gasket

But wouldn't either one affect the coolant resorvoir?

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1986 300SDL, 362K
1984 300D, 138K

Yes either one will affect the coolant and in either case if the coolant rises or starts bubbling the head has to come off.

I'm not aware of a combustion-to-coolant test that will distinguish between a blown gasket or a cracked head.

There are good chances that both your cylinder head and head gasket are in good shape and that it's something much simpler and easier to fix.

That's why a proper diagnosis like pressurizing a cylinder is so important because it prevents unnecessary repairs.

Thanks, that all makes sense.

There's something you probably don't know, I did a thread about it about Oct. '19. This car blew out its radiator near Eugene, OR. I happened to see the coolant light wink on in time to catch it from major cookage. Engine bay full of steam when I pulled over. What's unknown is did I heat it enough to put a tiny crack in the #14 head.

But I like your advice. I hate fixing the wrong thing and I've done that before.

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1986 300SDL, 362K
1984 300D, 138K