Oil Temperature Gauge DIY

[Jeremy5848]

In part because of the discussion in this thread, I decided to install an oil temperature gauge in my 1987 300D Turbo (W124, OM603). The other reason was that as an engineer, I like to measure things, whether I really need to or not. The surprising result was not so much the temperatures (engine oil 200ºF or 93ºC, transmission fluid a little less) but the time it took to get the engine and transmission warmed up.

This DIY is applicable to most engines, Mercedes or not. There will be differences in the way the senders mount and gauge placement is pretty much a matter of personal taste. YMMV. Caution: This DIY involves working under the car. Safety first! Never work under a car supported only by a jack. Always put the car in gear (or in Park), set the parking brake, and chock the wheels that are on the ground.

I purchased a VDO oil temperature gauge (model 310-106, range 120-300ºF). I would have preferred a Celsius model and they are probably available but I didn't search very hard. Since this is an electric gauge, I was able to add a switch and monitor not only the engine oil temperature but also the transmission fluid temperature.

Since I already had replaced the ashtray in my 300D with a 3-gauge panel and the panel was full, I had to make room. I decided that the voltmeter was not something I needed to look at all the time so I moved it to the glove box. The voltmeter is mounted in a little metal bracket (VDO 701-2142) and is wired to the light for the glove box. When the glove box door is opened, the voltmeter and its internal illumination come on with the glove box light.



Placement of temperature senders is controversial. Should you put the sender where the fluid is hottest, coolest, or what? Since I was looking for relative changes in temperature that might indicate a problem, it didn't really matter where the sender was placed. Put it somewhere convenient, get to know what the gauge reads under normal circumstances, and then watch for "abnormal" readings.

For the engine oil sender, the location was easy: I removed the drain plug in the oil pan and replaced it with VDO sender 323-055 that had the same threads (M14x1.5). With a cold engine, I didn't drain the oil, just quickly swapped sender for plug and caught the spill in a waste pan.



The transmission fluid sender was a little more work. The drain plug (M10x1) in the transmission pan points down and there isn't a lot of room between the plug and the belly panel ("sound encapsulation panel," as Mercedes calls it). I decided to remove the pan and drill a hole in the side for the sender. Since I could use any one of the many available senders, I chose VDO number 323-057 with 1/8-27 threads because it was inexpensive.

After draining the transmission fluid from the pan (about 2-1/2 quarts), I removed the pan and looked for a place where the sender could go without hitting anything. A place on the left (driver's) side near the back turned out to be best. The sender protrudes into the pan 1/2 inch and easily clears the filter, which lives back there.



A 3/8 inch hole, slightly enlarged with a reamer, provided the correct size hole. To be on the safe side, I used a nut and a crush washer on both sides of the pan and also used a little Loctite® 518 sealant to make sure I had a good seal. Note that 1/8-27 is a taper pipe thread, not a straight thread. I don't remember where I got the nuts but I think they were originally electric lamp hardware. This Rube Goldberg method is rather unprofessional but since there's no pressure in the transmission pan I suspected I could get away with it.



On the advice of Sixto (Hi there ) I ran the wires from the senders up through the floor of the car, using the same grommet as the neutral safety switch (NSS) and reverse light wiring. From there, the wires went into the console to the gauge panel. The switch is a miniature SPDT toggle, very non-Mercedes in appearance but also very small and, with its black handle, hard to see. I'll just have to hope that the concours judges miss it.

All wiring to the gauge panel is done with connectors so that I can take the panel out of the car and work on it at my bench. The oil temperature gauge occupied the middle hole vacated by the voltmeter. Because three gauges is a tight fit in the ashtray space, I secured the gauges with hot melt glue — there isn't enough room for the usual mechanical hardware. The gauge panel is homemade, a sandwich of zebrano veneer over birch plywood over aluminum. The panel is trapped between the radio and the shift console so it doesn't need to be additionally secured. This also makes it easy to install and remove.





Having finished the installation, I refilled the transmission. The fluid, filter, and pan gasket were changed only a year ago so I reused everything. I left the belly panels off so I could check for leaks and, after removing the chocks, started the engine and took the car down off of the ramps.

Today I took the car for a drive to see how the new gauge worked. As I mentioned in the first paragraph, it seemed to take forever for the engine oil and transmission fluid to warm up enough to show on the gauge. The coolant had long since reached its usual 80ºC reading when the oil temperature needle finally budged off of its stop. Part of this was probably because the car had been sitting overnight in the cool of the garage (65ºF) before I backed it out into a blazing 95ºF California afternoon.

After running a couple of errands, I put the car on the freeway and ran it up to the next town (round trip about 50 miles). It took a good 10 miles to get the engine oil (Chevron Delo-400, 15W-40) up to 200ºF (93ºC) and even longer for the transmission fluid (NAPA house brand, I think) to get up to about 180ºF or 82ºC. Once these temperatures were reached, they stayed put, even when I returned to city traffic and slower speeds. Perhaps this is due to the large thermal mass of the engine and transmission. The outside air temperature most of the way was 100ºF so I ran the air conditioning continuously. The interior of the car stayed cool and the engine coolant temperature never went above 90ºC. Boost was 6 psi at 70 mph with the EGT at about 650ºF as usual.

Returning home, I parked the car and let it cool off before putting it back up on the ramps. Finding no leaks, I put the belly panels back on. Tomorrow I'll repeat this test to see if the panels make a difference and I'll update this thread at that time.

Jeremy

[Bio300TDTdriver]

The switch is a miniature SPDT toggle, very non-Mercedes in appearance but also very small and, with its black handle, hard to see. I'll just have to hope that the concours judges miss it.


Why don't you see if one of your spare rheostat switches or the odometer reset knob will slide on to it. At least it will be from Mercedes then.

[Jeremy5848]

Originally Posted by Bio300TDTdriver

The switch is a miniature SPDT toggle, very non-Mercedes in appearance but also very small and, with its black handle, hard to see. I'll just have to hope that the concours judges miss it.


Why don't you see if one of your spare rheostat switches or the odometer reset knob will slide on to it. At least it will be from Mercedes then.

An interesting suggestion, thanks. Let me see what I can find in my parts box.

Today I repeated yesterday's driving test with the belly pans back on the car. Everything else was the same except it was about 10 degrees cooler today. Even so, the engine oil got hotter (almost 220ºF or 105ºC) and the transmission fluid stayed a little cooler (about 150ºF or 65ºC).

Without the belly pans, the wind from the road would have blown onto the engine oil pan, cooling it, while the hot breeze would then have warmed the transmission. (That's just a guess.)

Jeremy

[scottmcphee]

What's the white handled rod in your glovebox - are you a orchestral conductor?

[vstech]

I love the retro cell phone can snugglie cricket rules.

[vstech]

oh, and I'm submitting this to the wikki for sure!

[Jeremy5848]

Originally Posted by scottmcphee

What's the white handled rod in your glovebox - are you a orchestral conductor?

Not by occupation but I like to listen to classical music and "conduct" as I drive. I suspect the highway patrol would not be amused but I haven't been caught yet. In any case, your sharp eyes have indeed seen my baton, purchased in a local music store.

Jeremy

[Jeremy5848]

Originally Posted by vstech

I love the retro cell phone can snugglie cricket rules.

Found that in a car at the local Pick and Pull and liked its compactness. It rarely gets used but you never know! Thanks for the Wiki nomination, perhaps it will help someone some day. I've gotten so much out of this forum that it's nice to be able to contribute occasionally.

[1980sd]

I like the aluminum wood laminate. That's a good idea.

How 'bout some installed pics?

[Marvelicious]

With your love of gauges, maybe you should consider some of those Westach dual gauges: Egt and boost on the same gauge, that kind of thing. I think they look pretty much the same as the VDO stuff, so it wouldn't be a mismatch.

[funola]

Originally Posted by scottmcphee

What's the white handled rod in your glovebox - are you a orchestral conductor?

I thought that was a magic wand which Jeremy uses to turn those who text while driving into turds.

[scottmcphee]

Boost was 6 psi at 70 mph with the EGT at about 650ºF as usual.

That's less than 1/2 way to piston melting point, I wonder with stock IP if you could ever get to danger zone on EGT's? Maybe only if a squirter failed.

[Jeremy5848]

Marvelicious, I looked at the Westach gauges several years ago but the color choices at that time weren't as good as perhaps they are now. I'll have to look again. I agree it's the only way to stuff more functions into the available space.

Scott, although I've read many posts of overheating 603s, my diesel seems to be very well cooled. My EGT probe is located at the point in the trap cat recall pipe (does it have a name?) where the EGR valve used to be connected. The location of the probe, just before the turbo, might affect the temperature. I've never had an opportunity to drive the car up a steep mountain so the EGT has never exceeded 850ºF.



1980SD, the laminate is similar to what Mercedes uses. The purpose of the aluminum (so I have read) is to prevent the wood from splintering in an accident. Here's a picture, taken from the back seat (don't try this while driving ). Pardon the cheapo radio, it's what came with the car. I have a factory Becker with CD changer from a 1994 E430 waiting to replace it.

[Marvelicious]

Originally Posted by Jeremy5848

1980SD, the laminate is similar to what Mercedes uses. The purpose of the aluminum (so I have read) is to prevent the wood from splintering in an accident.

Thats why they did that? I've been refinishing my trim one piece at a time, and the whole time I've been cussing them for taking a piece of wood that they wanted veneer on and putting aluminum in the middle. I guess it does make sense from a safety standpoint, but from a "frustrated guy sick of re-veneering aluminum" standpoint it blows.

[1980sd]

Wow, that looks really sharp installed!