OK, I maybe over stressing about this....here is my situation:

I live in a rural area... I'm just not going to find Mercedes Benz brand antifreeze. I gather that there is some contention about which other types are going to be alright to use... I've tried the search function and found what I guess to be abreviations for other brands. If someone would post the full name/type of a brand that I would be likely to find in an Auto Zone type store, I would greatly appreciate it< major newbie here....please type slow so I can understand >

Also, I took the car to a "foreign car garage" when I first got it last month... an hour and a half away was the nearest I could find The shop was suppost to check everything over including flushing radiator/ changing the thermostat.... The guy said he didn't want to use the none MB brand thermostate I had picked up...he'd order a genuine MB part. when I picked the car up he said he had been too busy to get to that.... peak of the tourist season here in the mountains and all
So I'm hoping that I'll still gain some cooling effectiveness with just a flush and coolant change.
I understand that on steep grades it's normal for the temp to go up. Most times the car is running mid 80s to low 90s, but on a long steep grade coming home last night it got close to the 115/120 mark.... it still goes back down quickly after the crest of a hill... but I was.... well, stressed out last night

Thanks,
John

Xerex G-05.

Use Zerex G-05 coolant mixed with distilled water, available at AutoZone.

Coolant flush and change should be done every few years.

You probably won't gain much on a flush and a coolant change unless the system is full of rust and scale. In that situation, the change will do some good, but it would really need a citric acid treatment to effect any real benefits.

115C. is way too hot for that engine. You've probably got serious radiator issues. Pull the radiator, get some commercial condenser cleaner (phosphoric acid) and go to town with some compressed air. Take a couple of hours and get those passages pristine clean. They probably have never been done since the vehicle was new.

While some folks change the thermostat in a valiant attempt to cure the problem, it's very rarely the culprit.

The second critical item for low speed operation is the clutch fan. The clutches tend to lose the capability to engage and the cooling at low speeds is compromised. But, if it's running above 115C. on the highway, you've definitely got to address the radiator..........now........before you crack the head.

Brian,

My recent struggles to get my car running cooler have led me to develop some theories on coolant system troubleshooting, by analyzing the cooling system in terms of its two components, water and air.

The water side describes the circulation of coolant and encompasses alot of things: e.g. restricted radiator passages, restricted engine passages, inadequate opening of thermostat, etc.

The air side is much simpler, it is limited to the ability of the radiator to adequately dump the heat given to it by the engine. There are only two components involved in the air side of the cooling system (both of which you've implicated), the fan clutch and clean radiator fins. The air side is also easier to troubleshoot, since you simply need to observe the temperature of the lower radiator hose (coolant return line) to know if its working. Or more appropriately, you should measure the difference between the upper and lower radiator hoses. As you have mentioned in the past, the thermostat is fully open at 94 C. The coolant return line should be well below that. Quite simply, if the lower radiator hose is "cool" to the touch (less than 80 C) when the car if running hot the air flow is adequate.

That's valuable info. If we could establish that 80C. would be a good benchmark number for the return coolant temp, it would go a long way to help troubleshoot these systems.

But, I seriously question the number of 80C. It's hardly cool to the touch. Do you not actually mean 80F?

I'd also question the ability of the radiator to drop the return coolant to 80F. in 80F. ambients. In fact, I'll tell you that it's basically impossible.

My guess is that the return coolant should be somewhere around 40C. if the radiator is doing a decent job.

Even these numbers are a WAG, because they depend on coolant volume and airflow through the radiator. Increase airflow (drive the vehicle) and the return coolant temperature goes down. Increase coolant flow (increase rpm's) and the return coolant temperature goes up. Sometimes these two variables offset each other.

I agree with your evaluation, but 40C sounds a little low to me. If the engine is running at 80C, a 40C return temperature would mean the radiator would be reducing the coolant temperature by about 70F, my best guess would be closer to a 60C return temperature, a 20C (36F) difference.

I actually did measure the return coolant on the SD when I was trying to find out why it runs at 95C. depending on how it feels that day.

IIRC, the return coolant was about 120F...........or somewhere near 50C.

And, I suspect that the radiator is not all that efficient on the SD.

I'd surely hope that they would do better than 60C. at idle.

OK, I've never measured it myself. I'm just surprised it was that low, a 45C temperature drop is quite a bit for a single pass water/air heat exchanger (50C is only about 20 to 30C above ambient), but it is what it is.

I expect very few of us here buy our Mercedes anti-freeze from a retail store or dealer. We buy mail order from Mercedes Shop (this site) or some other on-line outlet. Typically you can combine enough maintenance parts to get the order total above the "free shipping" level and that makes the bulkiness of the gallon containers irrelevant.

You will do OK with the proper substitute, but your engine is particularly sensitive to having the proper coolant (with the aluminum head) and so I would strongly recommend MB coolant.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I'd probably suggest the opposite. The local availability of G-05 isn't that bad and, usually, you need it for the forthcoming weekend.........precluding an online order.

Can you get G-05 online at a reasonable price (with shipping)? I'd doubt it.........you're talking 16 lbs. to ship them.

I have had luck finding iG05 at the local NAPA stores.

I would try the citric acid flush making sure that you drain the block as well. You can get the citric acid on ebay. When I flushed it, I screwed in a 1/4 inch galvanized pipe into the block drain and attached a garden hose to the pipe. This way I could back flush with clean water and have the crud come out the radiator hoses. If that does not work, go to radiator.com and get a new improved version with a stronger neck. The part number is 473PL.

20 plus year old radiators can be beyond help

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Wow, thanks for all the replies! Got 2 jugs of Xerex G-05 and 2 gallons of distilled water... it says to use a 50/50 mix....any idea of the total volume inside the system.... ie: how much G-05 do I add before starting with the water?
I'll try my luck with another search for "citric acid treatment"... but a simplified explaination would be a wounderful thing....
I also have some very cool news.... I just met an older gentelman working at the Autozone....he retired up here recently, after having worked on Mercedes and Porsches for the past 50 years... He also said it could be the fan not working properly. He came right out to the parking lot and started poking around under the hood. Commented on how clean the engine has been kept on this car... he also sorta lamented that he doesn't really have any space at his retirement home where he can work on a car....
I told him that I could help him out with that problem I think I've made a new friend!

You need 5.5 quarts of G-05. Unless you're draining the block.........better add it straight.........or you won't get the required amount into the engine.

I'd strongly recommend removing the radiator and cleaning it with condenser cleaner. If you don't..........we'll be doing the "I told you so".........in a couple of weeks.

That sounds about right based on my experience. I haven't actually measured the lower rad hose temp, but I have done it by feel.

My basis of comparison is daily handling of bottles of molten agarose fresh from a 55 C water bath (55 C is just a little too hot to keep your hand there for more than a minute of two).

I put out the 80 C in my earlier post as a maximum temperature at which the return coolant would need to be for the thermostat to function as anything other than an "on/off switch". Agreed that 80 C is darned hot to the touch.

Basically I'd say that as a quick test if you can't hold on to the lower radiator hose without any discomfort, your radiator is not dissipating heat adequately (either debris in the fins or bad fan clutch).