Is there any way to get an accurate ATF temperature reading other than the pan? - PeachParts Mercedes-Benz Forum

shertex · #1 06-18-2015, 10:38 AM

Have the bottom panels off the the 98, cleaned things up, my only leak is a minor ATF leak from the torque converter area, which I will live with for the foreseeable future.

With my infrared thermometer, I can easily read the ATF temperature at the pan. Is there any way to do this once I put the panels back on, i.e. from the top of the engine compartment? I assume not, but thought I'd ask.

Incidentally, the attached graph is extremely helpful for measuring ATF level....since it isn't always easy to have temp at exactly 80C. Graph is fairly linear, though slope decreases slightly at higher temps. For every 10C, level changes by about by about 1 cm.

Kajtek1 · #2 06-18-2015, 11:26 AM

I drove my E300dt with visco fan and shrouds removed, so took me about 2 seconds to point the infra-red at the ATF tubing going into radiator.
The passenger side was the inlet, so was showing transmission temperature, while other side was going out and was colder.
Even with fan you still should see the tubings. Don't point the thermometer at the hose as rubber will fool the reading.

mach4 · #3 06-18-2015, 12:01 PM

I have a permanent temp probe mounted on the cooler line to the trans cooler. I believe this is reasonably accurate as the only temp drop should be radiation from the hardline itself and in the bracket the probe is mounted in. The bracket is aluminum to facilitate high heat transfer from the line, but I don't have it insulated on the other side so there is some presumably small temp drop.

Jeremy5848 · #4 06-18-2015, 02:39 PM

I put a temperature sensor in the transmission pan when I had an '87 300D Turbo. The gauge was one of the standard VDO electrical temperature gauges, mounted in a panel replacing the ashtray. (It's the center gauge in the picture. The little switch above the gauge allowed me to switch between engine oil and transmission fluid.) Probably more work that the OP wants to do just now.

The surprising thing (to me) was how long it took for the transmission to come up to temperature—a good 15-20 minutes at highway speeds. The engine coolant came up to temperature first, then the engine oil, and finally the transmission.

Jeremy

shertex · #5 06-18-2015, 02:42 PM

That's pretty clever, Jeremy.

jay_bob · #6 06-18-2015, 05:21 PM

The data is accessible via the diagnostic port as there is a sensor in the conductor plate. The FSM states to use either the HHT or STAR to read the temperature as part of the transmission service procedure. Not sure if you can pull it over OBDII with a ScanGauge or not.

Jeremy5848 · #7 06-19-2015, 01:53 AM

Quote:

Originally Posted by jay_bob

The data is accessible via the diagnostic port as there is a sensor in the conductor plate. The FSM states to use either the HHT or STAR to read the temperature as part of the transmission service procedure. Not sure if you can pull it over OBDII with a ScanGauge or not.

That sounds a lot easier. A feature that came along with the 5-speed 722.6 transmission?

jay_bob · #8 06-19-2015, 08:04 AM

Yes that is only on the .6 and later - earlier models have no electronics.

The .6 has a "conductor plate" in the valve body that holds and supplies the connections to solenoids and sensors.

Older transmissions determine their shift points by pressure acting on valves in the valve body.

The newer transmissions are "drive by wire", they take the speed data, both internally and from the engine, and command shifts by actuating the solenoids.

It's a two way street, the transmission can actually request the engine to momentarily drop power so the shift is smoother.

Also the transmission runs a sanity check between the input and output, if the input speed and output speed are not plausible based on what gear the computer thinks it is in, you get the "limp mode" to hopefully prevent damage.

Computer magic and CAN bus...

Diesel911 · #9 06-19-2015, 10:08 AM

The Pan temp sensor tells you what the temp of the Fluid is as it goes into the Transmission.

If you want to know the Highest Temp of the Trans Fluid as it comes out of the Transmission you need to get a temp probe on the Trans Oil Outlet Line going towards the Radiator.
To get they you have an issue of where to put the Probe.

For a temp check there is Digital Meat Thermometers that are made for sticking into a Turkey or something similar and they have a 3-4 foot cord that goes outside of the over and the Thermometer has Magnets on the back and that allows you to stick the Thermostat on the Oven.

The Probe is about 4-6 inches long and about 3/16 of an inch thick. You would strap the Probe to the Trans Fluid outlet tube and then cover the whole probe with insulation. Run the cored to the outside and the Magnets will hopefully hold the Thermostat to the Hood so you can see it while you drive.

like I said that is only good for a check; not good to monitor the temp all of the time.

Jeremy5848 · #10 06-19-2015, 10:37 AM

Point taken. The correct way isn't easy so few of us do it.

Since the OP is primarily interested in watching the fluid temperature increase as a function of a leak, measuring the temperature anywhere and watching for changes over time has value. Your meat thermometer suggestion, for example, would work.

mach4 · #11 06-19-2015, 11:04 AM

Quote:

Originally Posted by Jeremy5848

Since the OP is primarily interested in watching the fluid temperature increase as a function of a leak, measuring the temperature anywhere and watching for changes over time has value. Your meat thermometer suggestion, for example, would work.

As one who has a temperature gauge installed, I don't think that "changes over time" will be meaningful as the temperature changes fairly dramatically based on ambient temperature, load, hills, speed etc. it would be almost impossible to distinguish between "normal" changes and those due to level.

shertex · #12 06-19-2015, 11:41 AM

Once (if) I put the panels back on, I'll only have two options: measuring at 25C and measuring at 80C. The only way I can roughly ensure 80C is a straight highway run for 15 miles or so. It's amazing how quickly temp starts to drop, though. Makes for a lot of unnecessary driving just to get ATF level right.

Diesel911 · #13 06-19-2015, 12:26 PM

On mine the ATF Cooler is built into the Radiator. That means the ATF going back to the Transmission is not going to be much cooler then what the Engine Coolant Temp is.

Then hot ATF that leaks past Trans internal parts is going to mix with the cooler ATF from the ATF Cooler in the Pan.

biopete · #14 06-19-2015, 02:36 PM

Quote:

Originally Posted by shertex

Once (if) I put the panels back on, I'll only have two options: measuring at 25C and measuring at 80C. The only way I can roughly ensure 80C is a straight highway run for 15 miles or so. It's amazing how quickly temp starts to drop, though. Makes for a lot of unnecessary driving just to get ATF level right.

No you don't. Just add some data points yourself by driving and checking it every few minutes. You probably know what i mean but for example -- Once you know it is the exact right full level, like after you get home from a long drive and top it off if it needs it, then let it cool. Then start car and check it -- make a mark or take a picture. Drive for 5 miles / 5 min or whatever -- make a mark, drive 5 more min , make a mark, etc etc, until its up to 80C mark . Then you'll have a decent idea where it should be after X min of X type of driving in the Summer.

Honestly though, as long as there is some on the stick between between the hot and cold mark, you aren't going to do any damage to the transmission if you just wait til you get to a convenient place to top it off. There are 8 quarts in that thing and being 1 pint low for a day or two won't hurt it.

How bad is the leak though?

biopete · #15 06-19-2015, 02:37 PM

Why does the fluid level rise as it warms up again?