'79 300D, 447,000 miles. Needs more power. Where to start?
 

As the title says, I own a 1979 300D non turbo with nearly 450,000 miles on it. I just bought this car about 3 months ago, and the previous owner had been running it on WVO for the last 50,000 miles. I'm currently running on mostly new veggie oil, and 5-10 gallons of diesel per fill-up. I understand it's a diesel, it's old, and it doesn't have a turbo, but I'm pretty sure it has much less power than it's supposed to. My main complaint is uphill. There are a few hills my car has to climb every day to get to work and back (yes, it's my daily driver), and it has a very hard time doing so. If I get a lot of momentum built up, I can usually make it over the hills at the speed limit, which is about 45mph. If the hills were any longer than they actually are, I'd eventually get down to about 35 or 40mph. I don't need to go any faster than that, but if I have to stop or slow down for signals or other cars, I basically can't get back up to the speed limit until I'm going downhill again. My assumption would be to start with fuel filters, and I just changed the air filter tonight. If anyone has any other ideas, please let me know what else I might be able to do. Thanks in advance. And please don't tell me to adjust the ALDA screw, the non turbo's don't have them.

how much blowby is present at operating temp?

I honestly don't know how to find out. I've been told what blowby is, but don't know how to check it out. I was trying to sell this car last month, but didn't have any luck. One potential buyer took it in for a compression test, and told me it came back good. I never saw any paperwork though, so who knows. A Mercedes specialist near my work told me if I wasn't losing any (or not too much) oil, my compression was probably fine, which I'm guessing is what you're getting at with the blowby question.

That is correct. I would suggest a compression test before you start dumping money on parts. There are cheap test kits available that will give you reasonably accurate readings - thats all you really need.

@ 450k, its the most likely culprit for consistently low power without other obvious signs of failure.

to do a rough test for blowby: remove oil filler cap with engine running and at full operating temperature. Determine the amount of 'shake' or 'dance' that the cap has. This is gas getting by your piston rings and blowing into the crankase causing positive crankcase pressure, which makes the cap dance.

Remove oil filler cap, or let it sit on the filler hose to see if it moves? Where would I get a kit to test compression myself? Would I possibly be better off just having this done by a mechanic, or is it pretty easy and obvious?

youtube has a video of the blowby test.

I got my comp tester at harbor freight. For the price, I am impressed with it.

What is most complicated task you have successfully completed mechanicaly?
The test is not hard, but unknowns will haunt you on an unfamiliar engine.

Most complicated task? I guess replacing spark plugs and c.o.p.'s on a 2003 F150. Pretty mild stuff, but I don't mind getting dirty and have plenty of time. On this car, I haven't done any work at all yet. I have had work done, like valve adjustment, but nothing myself.

This is an obvious tell-tale of my lack of w123 knowledge (or any car, for that matter), but what if the compression is bad? Motor needs a rebuild? I was told the motor had a "top end rebuild" sometime in the last 100,000 miles, but have no records of this. Thanks for all the help. I'm coming here from another Mercedes forum that didn't yield as much help, and gave constant replies such as "your first mistake was...", basically giving no help at all and talking only about the reasons alternative fuels should not be used. I know veggie oil isn't the intended fuel for my car, but with a small conversion and a motor with nearly half a million miles, I figure it would be the perfect car to save some cash and give the veggie oil a shot. It's nice to have answers that don't revolve around "all your problems are from using veggie oil...".

Use Diesel, get all your maintenance up to spec, use synthetic fluids and adjust the ADA 1/4 turn CCW.

Probably wouldn't hurt to get your injectors inspected/tested, given that the PO had used WVO of who-knows-what-quality or filtration for 50K miles.

Compression and Leakdown Test..
 

Hello,

I would first do a compression and leak down test. An engine with that many miles certainly will have some wear in the bores. If it's really worn-out, you will be able to make a decision on rebuilding, continue to drive as is, or if you really love the 123 chassis, finding a better example. The non-turbo didn't have the power (85hp?) that the turbo units have.

In my opinion (and after spending hundreds to rebuild a 77 240D), a car with that many miles is not worth an engine rebuild. On my 240D, I thought I could just do the liners, pistons, rings and slap it back together...but once you open it up, you'll have to make decisions on the rest of the "worn-out" parts...the valves, the valve guides, timing chain, timing chain guides, the camshaft...it never stops! You end up throwing money at a worn-out car.

There are many fine 300D Turbos in the 123 chassis out there. Find one of those and you'll never go back to the "normally aspirated" diesel again.

Just my 2¢ worth...

The Tenor Man

The funny thing is that I did find a turbo diesel that I bought and sold within a week. I think the trans was bad and one of the rear axles had problems, along with an exhaust leak I didn't feel like fixing. So, I sold it and kept my '79. People are scared of the mileage on my car, but I may try to sell it one more time and pick up a TD.

WIth that high mileage a motor rebuild would be in store. Do a compression test on it and see what it reads.

How much (on average) would a decent rebuild on my n/a motor cost? I know we're talking in ball park figures here...