When I bought my 300D, the PO had a 617 from a wagon in his backyard that he threw in to sweeten the pot (aka reclaim his backyard from rotting Mercedes junk). We had a CJ7 with half an engine that had been sitting in the garage for the last 8 years, so we decided to try our luck and improve on the anemic performance and low single digit MPG that the old 258 was providing before it dropped a cylinder.

Long story short, we mated to the jeep's stock T5 transmission and resurrected the engine (3rd one, starting to get pretty quick at it!) and we now have it road legal and insured.

However..... Top speed is 60-65 mph and the temp starts to creep in 5th gear (which is WOT to maintain speed). We're in deep South Texas, so its all flat. No hills to mess with.

While I understand that drag and everything play a large part into top speed, seems that other people's experiences with this swap is that they are at least able to maintain highway speeds and some of the even tow trailers!

Specs:

1983 OM617 from 300TD (150k claimed miles, but who really knows)
4.88 ring and pinion
Alda removed
11lbs of boost from a Garret turbo
33x12.50x15 tires
5 inch rough country lift
Overdrive ratio is 0.86
Brand new MB thermostat installed in December
Tarus dual electric fans, jeep radiator

According to the gear ratio calculators, 4.88s and my tire size should put me close to 3200rpms @ 75mph. Which is right at why my 300D does at the same speed.

My main concern is the heat issue, as it holds temp until you shift into 5th or pin it fighting a headwind in 4th. And this is all in 50 degrees or cooler temperatures!

What can u do to keep my temps down?

Am I correctly thinking that my egts are increasing at wot and that make my engine heat up? I don't have a pyrometer installed so I have no idea on how things are on that front.

Y'all have been a huge help with my other Mercedes, hope there is some direction available now. Thanks!

P.s. threads are worthless without pics

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