1987 300TDT Oil Pressure Gauge
 

In addition our latest addition, I am trying to keep my daily driver as healthy as possible.

For the last month or two, the oil pressure gauge in the instrumentation panel has been...goofy. The gauge sits as 0 until the engine is started. Once started, it shoots to 3 and stays there until I turn off the car.

Prior to two months ago, the gauge would glide between 0 and 3 depending on the RPMs of the motor.

Any recommendations on where to start troubleshooting this one? :-)

Thanks To All!!!

glenn

I'd start by replacing the sending unit. It's inconveniently located on the side of the oil filter tank...best reached from below, if I remember correctly.

it shoots to 3 when the motor is started, or when the key is turned on?

Thanks for the replies!

The needle shoots to 3 as soon as I have the key in the "on" position. The engine is not started...

glenn

Yup. Typical failed sending unit. Likely it leaks oil anyway.

Please forgive me Gentlemen. Is the oil pressure switch another name for the "sending unit"? If so, do I go with the $25 or $50 part (1987 Mercedes-Benz 300TD Base Wagon - Oil Circulation - Page 2)

If these are not the part, can someone please point me in the proper direction?

Lastly, as I just picked up another 603 engine, should I replace the units in both just to be safe? :-)

Thanks for sharing the expertise!!!

glenn

In post 4 of this thread, I link to some other threads which helped me replace the oil pressure sender on my om603:
http://www.peachparts.com/shopforum/diesel-discussion/339275-87-300td-om603-960-oil-pressure-sensor-replacement.html

The sender is pretty buried in the engine compartment, and I didn't want to do it again any time soon. So I went with the VDO option in your link. It is (probably) the same item that MB would sell you with their star on it. And yes, what we refer to as the oil pressure sender or sensor, apparently Peachparts refers to it as a oil pressure switch. So yes, you found the right items. I am not familiar with the other brand, so I have no advice there. Their website is describes the company a little. I guess it is Spanish.
Introduction

Thanks for the reference posts Shortsguy1. One last question. You refer to a crush washer for the installation of the actual sending unit. Is this necessary? If so, do they have them on Peachparts?

Thanks for the pointers!

glenn

According to a competitor of PP, the crush washer is part 007603-012102. It costs only $.25, so buy one via PP when you order the pressure sender.

Yes, in my opinion, you want to use a new crush washer to ensure no oil leaks.

I have done this job it is not too bad.

First disconnect the battery, the + terminal on the starter is close to the sensor and you don't want to cause a short.

When I looked at it, I first thought about going up from the bottom but the starter is in the way.

I ended up going at it from above. You'll need to remove the intake manifold. So pick up a new intake manifold and cross over pipe gasket as well.

I would also check the condition of the injection line clips while you are removing the manifold. If any are loose or missing I would replace them all. The plastic gets brittle with age. If you don't secure the injection lines properly they will vibrate and then leak.

And of course you will find the manifold is plugged up with EGR deposits. That's another squirrel to chase.

Drain about a gallon of the coolant into a clean container (use the red drain plug under the radiator).

Disconnect the fuel preheater at the left rear corner of the block and move it out of the way. No need to disconnect the fuel lines but you will need to remove the heater hose connection. Get a new o-ring for this as well. It just pulls out of the block after you have removed the clip holding it on. Stuff a clean rubber glove into the port in the block to keep coolant from dripping and keep contaminants out of the hole.

Now you have clear access to the oil pressure sensor. It is a little silver can at the base of the oil filter. When you remove it you will lose maybe a teaspoon of oil so no need to drain the engine oil first. The electrical wire just pulls straight off the pin connection and the sensor unscrews from the oil filter base.

When you go to put the coolant back in, use a funnel with a coffee filter in it. Remove the upper radiator hose from the radiator and pour as much of the coolant as you can directly into the block, much faster than trying to put it back in through the tank. This also helps the trapped air pocket escape from the head.

Jay-Bob
Were you doing any other jobs at the same time? You removed a few of things which I was able to leave in place, so I was wondering if you perhaps did glow plugs at the same time or anything. Specifically the intake manifold and the coolant were aspects I didn't do, and I don't have small hands nor great mechanical abilities.

Clearly there is more than one way to skin a cat. Some people have good success working from below, but I could not get any of my tools onto the sender to remove the old one. As previously linked to, I followed post 10 of this thread. It was perfect. I didn't do step 1 though.

http://www.peachparts.com/shopforum/diesel-discussion/162412-603-oil-pressure-sending-unit.html

I had recently done glow plugs so my manifold was relatively easy to remove (i.e. bolts not seized). And I remembered the tricks for getting each of the manifold bolts out. I can pull a 603 manifold in under an hour. (606 in about 20 minutes).

Once I removed the manifold and the fuel heater it was child's play to change the sensor. I also had to change the 2 heater hoses down there because they had gotten oil soaked and soft.

I figured I could fight and struggle all afternoon trying to reach in there to change the little bugger or just move the stuff out of the way and reach right in.

I also don't have a huge assortment of tools so the wrenches I had at my disposal would not fit without that stuff out of the way. If I had crow foots or bent wrenches I probably could have reached right in and pulled it out.

While I had the left side of the engine exposed it gave me a chance to inspect and clean things down there as well. The oil had leaked all over everything.

Finally replaced the Oil Pressure Switch yesterday. Thank You all for pointing me toward instructions. They were VERY helpful! It was literally a 30 minute job. :-)

I was nervous after installation. Once I started the car with the new Switch, the dashboard gauge still shot to 3 and stayed there. Today, after a 15 minute highway drive, the gauge dropped back to 2. Another short drive and it dropped to around 1.5.

Very nice to have this working again! One last question. Should I put some type of conductive coating on the electrical connectors? If so, recommendations?

Also, I have pictures. I have not looked at them yet. Should I just attach them to this post?

Thanks Again!

Your gauge behavior sounds normal. Goes to 3 and stays there with a cold engine. As the engine warms up, the oil flows easier, and the pressure will drop down into the 1's or 2's at a red light. As soon as you accelerate the pressure should pin at the 3 and stay there as long as the engine is running above idle speed.

Manage the pics with an advanced post. That way they stay on the server, not a web host.