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Old 09-16-2004, 11:54 PM
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Join Date: Sep 2004
Posts: 2
300D conversion to 300 Turbo Diesel

My father is attempting to install a remanufactured 84 300 Turbo Diesel engine and transmission in his old ’81 300D. It’s a grand undertaking to be sure, but he has some questions, so I thought I’d post them here to see if there are any experts that can give him some advice. He believes the swap will be pretty straightforward, except for the following four items:

1. If you examine the first picture attached, you’ll see a “Turbo Pressure Switch”, labeled as item number 12. Since there is obviously no wiring for this setup in the 81, my father would like to know how to properly wire and fuse this item.

2. If you examine picture number 2, item number 7 is called a “Switch Over Valve”. There was no such animal on the ’81, so how exactly it will be hooked up properly on the ’81 is a mystery. It can’t be seen in the scanned picture, but the connections on the valve show the left connection heading “To Manifold” and the right one “To Aneroid Compensator”. I have no idea what an Aneroid Compensator is. Maybe you kind folks can help.

3. Looking at picture 3, you can see that the “Transmission Inhibitor Switch” is round. On my father’s 81, it is rectangular. The problem is this; on the reman 84 tranny the switch is round. Can the wires be simply spliced from the old switch and hooked to the new round one?

4. On the older 81, apparently there is a vent pipe that runs from the air cleaner to the oil pan, On the newer engine, it is eliminated. Is it necessary to hook this up? Does he need an air cleaner system specifically for the 84, or will the 81 work by simply closing of the air cleaner’s connection to the vent pipe?

Lots of questions, I know, but I hope you can help. If not, can you point me to any other MB forums which might be able to be of assistance? Thanks again.

PS Any other tips on this conversion would be gladly appreciated.

Attached Thumbnails
300D conversion to 300 Turbo Diesel-pressureswitch.jpg   300D conversion to 300 Turbo Diesel-switchovervalve.jpg   300D conversion to 300 Turbo Diesel-transwtch.jpg  
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Old 09-17-2004, 12:16 AM
Stressed Member
Join Date: May 2004
Location: Florida Big Bend region
Posts: 721
There's an entire "Diesel Discussion" subforum. I suggest posting your questions there for best response.

Also, welcome to the ShopForum! I think there are folks here who will be able to provide you with (or direct you to) all the information your father requires for this project.

-- eskimo

Last edited by Eskimo; 09-17-2004 at 12:24 AM.
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Old 09-17-2004, 10:50 AM
Hatterasguy's Avatar
Join Date: Nov 2002
Location: Milford, CT
Posts: 19,318
Post this in the diesel forum, they would be able to help you a lot more.
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Old 09-17-2004, 12:22 PM
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Join Date: Jun 2001
Location: Northern Calif. (Fairfield Area)
Posts: 2,225

Since we are both already here I will try to answer your questions. The boost pressure switch is an over boost protection. If the boost gets to 15 lbs, the boost to the inj pump is dumped so fuel is reduced. I'd have to dig up a wiring diagram for you, but I'd be inclined to bypass the circuit.

Who ever built the 84 engine installed the wrong oil pan. I hope you didn't get the engine from ATK. They are the worst rebuilders in the business. That tube is part of an oil separater built into the air cleaner. The system is designed to drain blowby oil back to the pan. The early turbo engines in the 116 chassis didn't have this feature. I've seen rebuilders screw this one up before.

Youd dad is going to have to salvage an exhaust system from a bone yard, because, because the turbo exhaust is much larger.

He may have to get a new glow relay, or take the harness off the old engine. I'm not sure on this one.

He will also be cranking up some high ripums on the highway until he changes the differential.

Good luck,

Auto Zentral Ltd.
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