OM617 Lacking top end/ gets hot in 5th ~ '85 CJ7
 

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

Sorry for the crappy cellphone shots...

Are you certain the radiator and/or block aren't plugged with gunk? Another thing that comes to mind is water pump. As for power, is the ALDA adjusted all the way out? Also, there's a check valve in the return circuit on the pump that controls lift pump pressure and if it wears out it can result in power loss. Those are about the only things I can think of, except for maybe filters and make sure there's no fuel restrictions

Also dumb question but there isn't a chance the thermostat went in upside down is there?

Also valve adjustment and injection timing could have some affect also

Sell the 33" tires and get something significantly smaller to give a lower gear ratio. You want to be running at least 3000 rpm in top gear for decent cruising. And perhaps the radiator will not be big enough.

The Alda is completely gone. All valves have been adjusted and are within spec. Thermostat is in the correct way. The filters are new, but the tank is significantly worse than we thought. When the weather warms up we are going to drop the tank and clean it.

However, I have not been able to time the IP yet. Its on the list of things to do.

You're talking about the check valve that is on the return side of the IP, correct? I bought a new one this week but haven't had time to install it yet.

The rad could stand to have a shock treatment, but I don't think there are any major restrictions.

We have it geared for 3000 at 70mph and 3200 at 75mph. So our math seems to be close. And front rough measurements, the jeep rad actually seems to be close to the same size.

Edit:We have it geared for 3000 at 70mph and 3200 at 75mph. So our math seems to be close. And front rough measurements, the jeep rad actually seems to be close to the same size.

Edit: CJ7 radiator core size = 15.56 x 23.25 x 1.25 in
300D radiator core size = 16.69 x 21.13 x 1.25 in

So the jeep's is slightly larger.

You've definitely got a low power issue and also an overheating issue.

ALDA totally removed, hmmm... Too much boost from the turbo and too much fuel from the IP and you could be in piston melting territory, but I don't think so given the lack of power.

Low power: I think you need to go over just about every aspect of the set-up to ensure you are missing something.
- As already mentioned, adjust valves, fuel filters, fuel flow/volume, IP timing.
- How much boost is the turbo providing? I think you want to aim for around 12 lbs.
- EGR still in place? If failed open, that will rob some power.
- Exhaust restriction?

Start simple/easy/cheap and work your way toward complex/expensive.

I'd start with adjusting the valves and setting the IP timing, then check compression, then put a clear fuel line in the fuel return line and watch for bubbles.

And I can live with the low power and just keep it in 4th, but it is the overheating issue that really bothers me. But I feel like they are connected.

The way that I understand the Alda is that it only restricts pre boost levels of fuel. After it registers boost, it no longer limits fuel. Correct? So there would be no additional fueling in the higher RPM range.

I am running 11psi floored, cruises closer to 9psi.

EGR is still in place, but not connected to any vacuum. Hadn't thought about it being an issue... Had plans to block it off later on anyways. Move that up on the list of things to do.

Exhaust.... Is practically non existent. The flex pipe was broken when we got the engine, so that is where it dumps at.

We have clear fuel lines for the injectors and the return. We were sucking air through a pin hole leak, but that is now fixed. Slight change but nothing earth shattering.

I feel the timing is retarded some, because we have great low end at the moment. I should shoot for 24* TDC? Most people seem to like 25-27 range for their cars from what I've read.

I just advanced my timing as far as it would go because that was the closest I could get it to being correct via the drip method, and I don't think you need to worry about melting anything as long a you have an exhaust temp gauge

Neat swap. Love how it all fits under the hood and looks stock from the outside.

When you say "gets hot," how hot do you mean? My temp sits at 190F rock solid, except when I'm loaded and pulling a hill with my foot flat on the floor for minutes at a time, then the temp will creep up to 210 or so. Well within acceptable range. Goes back down when I get back to the flats. I'm running 31x10.50's and stock gearing on my swap. Engine has a new water pump, new thermostat, and the stock MBZ radiator.

4.88 with 33's is pretty low for 70 mph. It's what you want, but if it's going down the road a lot I would put in 4.10.

Kid, did you just bump it over tad and call it good? That's what I'm understanding. Also, NO exhaust temp gauge.

Thanks Yota, its a total blast to drive around town. They only way to tell from the outside that we changed anything is the oil cooler lines we had to cut holes for in order to get the cooler to fit between the rad and the front slats.

I was wondering how long it was going to take for some to ask about specific temps. The gauge is way off. So I'm not sure. "250*" is where it stays at around town and at idle. Anything below that and the thermostat doesn't even warm up or have the system start to build pressure. When it gets "hot" it will move up past the 280 mark. Its an electric universal temp gauge. How did you get yours set up? I want to put analog gauge in, but the probe was too long.

I thought long and hard about going to 4.10 or 4.56, but I wanted to have more power throughout the range and top out around 80-85mph. And if I can't hit 70mph with 4.88s, 4.10s wouldn't be doing me any favors.

I'd recommend getting an accurate coolant temperature gauge so you know where you're at and what you're dealing with. It would also be good to have an EGT gauge and boost gauge to assist with troubleshooting.

I'm kind of a gauge-aholic though, with temp sensors for intake, oil, trans, engine bay and EGT, pressure sensors for vacuum, boost and fuel as well as a voltage sensor.