Strange shift behaviour in arctic conditions 300D - PeachParts Mercedes-Benz Forum

evranch · #1 12-20-2024, 10:57 AM

OK, no vehicle likes the cold, but this one had me wondering if maybe there's too much transmission cooling at highways speeds when it's really cold. Is the auxiliary rad under the bumper an oil cooler or transmission cooler?

The car has been working great, but I was driving home from the city on an arctic day (-25C) and after 3 hours cruising at highway speed came up to a T intersection. I pulled the shift lever back to 3rd, but nothing happened. I used the brakes to stop, made the turn, put it back to D and then the transmission was reluctant to upshift through all the gears, hanging on to the gears longer than it should.

Since I was now driving only 80kph on icy roads, it was reluctant to shift to 4th, forcing me to take it to about 3500 RPM and pull my foot off the pedal to finally get a shift.

It's perfectly fine now that it's warmer and on shorter trips. Fluid levels are normal. Is it possible the transmission cooler sucks all the heat out of the transmission under these conditions?

Diseasel300 · #2 12-20-2024, 11:53 AM

Transmission cooler is in the radiator tank. The transmission oil should be at the same temp as the coolant in the radiator. If you have a stuck open thermostat, perhaps your coolant temps are way too low. The aux radiator under the bumper is an oil cooler, not transmission.

evranch · #3 12-20-2024, 11:59 AM

Thanks, coolant temps were rock steady at 80C so that setup should have been warming the transmission oil.

However if the thermostat rarely opens, then the radiator itself is going to be pretty cold under those freezing wind conditions. So maybe I should put on the winter front to keep it warm.

I cut a piece of bubble foil to make a winter front last year and keep it in the trunk, but I haven't been using it this year as it's annoying on warm days (around freezing) to have to pull over and remove it. If I didn't pay attention and the aux fans kicked on, they would not like it at all.

Diseasel300 · #4 12-20-2024, 12:43 PM

If the thermostat isn't opening because the ambient temp is just too cold, or if it's rarely opening and not enough to flow much coolant through the radiator, it kinda stands to reason that the coolant in the radiator is gonna be pretty frosty too. Glad it's you in those conditions, I'm allergic to the cold

Sugar Bear · #5 12-21-2024, 01:51 PM

Isn't the TStat opening supposed to be 87°C vs. 80. I'm not sure with the 300D but my M272 in an E350 gas is 87°, 7°C is a difference.

vstech · #6 12-21-2024, 03:58 PM

Quote:

Originally Posted by Diseasel300

Transmission cooler is in the radiator tank. The transmission oil should be at the same temp as the coolant in the radiator. If you have a stuck open thermostat, perhaps your coolant temps are way too low. The aux radiator under the bumper is an oil cooler, not transmission.

I thought the oil cooler was in the fenderwell, and the trans cooler was under the bumper.

Hmmm.

evranch · #7 01-11-2025, 09:53 AM

Just an update for any other unfortunate arctic dwellers, this problem has been 100% resolved by using a winter front. Just a piece of reflectix bubble foil tucked in front of the aux fans, I've taken it out for several long and cold drives with no recurrence of the issue.

Temps with the winter front never exceed 80C unless ambient gets above -5C, and when it does there is plenty of time to pull over and remove it before the aux fans kick in.

The only issue I'm seeing now is excessive consumption of my light winter oil (10W-30 synthetic blend) as it appears to be getting slurped through the breather when the block is not being chilled by the arctic blast. I'm steady draining it out of the catch can. Maybe time to go back to 15W-40 as I run a pan heater anyways.

Sugar Bear · #8 01-11-2025, 03:07 PM

What temps does the engine reach in the summer? I'm wondering if the coolant thermostat is operating, it shouldn't open until 87C. How cold is it in your region?

hercules · #9 01-11-2025, 03:58 PM

On the 126 body, I used some card board in front of the radiator ,leaving a gap up top
of 2 inches ,stayed there all winter.

evranch · #10 01-11-2025, 07:20 PM

The stat is definitely working as the gauge always comes up to and sits bang on 80 regardless of season. When I lost my fan clutch last spring it would rapidly rise above 90 when climbing hills, but would come back to 80 with highway airflow.

The gauge or sender could easily be off by a few degrees, I've never checked the coolant with a thermocouple. Or, someone could have installed a cooler stat I suppose.

Right now it is -18C and will be around -28C by morning. Then in a couple days it will be +1C during the day. It creates a lot of ice and makes it really hard to choose a winter oil - in our farm equipment we always have run fluids with wide viscosity ranges. Otherwise we would be swapping hydraulic fluid steady.

Sugar Bear · #11 01-11-2025, 08:07 PM

That's cold...what blend of fuel or # fuel do you run at those temps? I put synthetic oil in the freezer overnight and it was amazing to see how well it flowed.

dieselbenz1 · #12 01-11-2025, 08:39 PM

I've driven my old 92 300d without any protection using 0 40 weight oil when it would regularly be -40 without any issues

Sugar Bear · #13 01-11-2025, 08:47 PM

They must blend the fuel well locally for winter use. I've had fuel in the NY/NJ area gel at 5 F.

evranch · #14 01-12-2025, 06:16 PM

For fuel we just run commercially available "winter diesel" that becomes available in October every year. Good all the way down to -40 but has about 30% less energy content than "summer diesel". Here on the farm I keep a large tank of summer diesel and a small tank of winter diesel at hand. That way I can take delivery of whichever is available.

Mixing the two fuels results in blends of uncertain performance and is not recommended. I try to run the car down to at least 1/4 tank before filling with winter. Tractors often get siphoned out and refilled depending on how much fuel is left.

Summer diesel will gel at around that same point you mention, -15C (5F) but can cause filter plugging all the way up to -10C in fuel systems with no active heating. I've had my chore tractor come to a halt while plowing October snow before, resulting in the better part of the day spent siphoning and bleeding filters and pumps. That's why I remove summer fuel from my equipment in October now.