Finally tested compression on my 300D
 

I was worried that this car might have skeletons in the trunk. Only 135K when I got it, near cherry in and out but a wee bit gutless. Not bad for longer trips, will cruise at 65 to 70 but that's about top speed. Also had trouble cold starting in Dec. in Oregon - about 32° and later in WA at about 38°. Lengthy grinding, was getting worried about draining the battery. Or damaging the starter. Would rest about 2 minutes between 10 second spells of grinding.

I had read that poor compression could be a cause of poor cold starting.

The compression test news was surprisingly good: 1 through 4 - 380psi, 5 - 360. I'm thinking to do it again starting with #5. But I'm guessing this means that trying to get it running well is doable w/o breaking the bank. My '81 300SD was much peppier and that model weighs 300 lbs more.

I haven't yet done a lot with it. I feel stupid in admitting it, but I didn't get the title when I bought it. My SDL had blown a radiator the day before, I wanted to buy the 300D at the indie lot I'd been towed to, stayed overnight, got the cash together, basically jumped through hoops to make it happen. I hand him the money and hold out my hand for the title. He said that the garage owner keeps all the titles at his house for safekeeping and he was 20 miles away taking care of his wife at a hospital and they'd mail it to me. I didn't like the sound of it but I needed to be on my way to make a deadline, I wanted the car, and this wasn't just some guy with a sign in the window. The garage had numerous good Yelp reviews.

Long story short, after two stalling episodes by phone over the next two weeks he said the wife was back home and couldn't find the title. He said he would get a replacement, after a few weeks I discovered this was blowing smoke. The lady who sold the car to the garage has been amazingly helpful, we completed the application for new title Dec. 21st. DMV called a few days ago, it all looks good, I might have it by Feb 1. Bought it in mid Oct., purchased two 21 day 'light vehicle trip permits,' you only get two.

So I haven't put a lot into yet. Was reluctant to invest more until I knew I could get it off the 'paperweight' square and actually legally license it.

I'll next take off the intake manifold, inspect and clean. Perhaps trying to weld up the EGR so it looks functional but is actually deleted.

I saw an old post from Diesel911 about things to check/overhaul before rebuilding the turbo but I can't find it. Thought I bookmarked it.

Check fuel injectors. Sounds like my car - got it with 133K. It would barely hit 60. With new injectors, it does 90 with far less oil burn.

Does it smoke? Does it knock after it's warmed up? Those are both indicators. Also check throttle linkage (unrelated to injectors). Make sure you can really open it up when you're on the pedal. It's possible that the hard start is caused from myriad issues - injectors, valve adjustment, and glow plugs.

Henry C.

looking at you compression numbers I would do this:

- rebuild the injectors
- change glow plugs and ream the carbon out
- valve adjustment

do that and it should improve your cold stating

check your overboost protection system.
check the boost pressure at the ALDA and intake (could be a plugged line)

not easy on a om617 because the intake and exhaust manifolds and the turbo/all the drains are on one side of the engine

As suggested by Cleeves, check your throttle linkage goes all the way to the stop on the IP when the accelerator pedal is pressed to the floor. If the rods are out of adjustment or the pivot on the firewall is wasted, you won't have full travel on the IP. If it seems to accelerate ok, it's unlikely to be a turbo issue, steady-state cruising only generates a small PSI boost state anyway, so you should be able to do in excess of 70 even if the turbo were fully non-functional - it would just take a while to get there.

Cold starting is most likely to be glow plug issues as mentioned above. It could be one or more of the plugs or it could be the strip fuse has a crack in it. The compression numbers aren't terrible, but certainly lower than I'd expect for so low of mileage. Definitely adjust valves. My SDL had compression of 360 on one cylinder and 380 on the rest. It still started fine even if sat outside in below freezing temps overnight.

Proper Maintenance
 

Copy post # 3 and follow it, don't touch the intake manifold just yet ~ there are myriad things you need to do first and in the proper order or you'll just be chasing your tail in circles .

Assuming the odometer works (unusual) you prolly have a very good car there once you get it fettled .

If the valves were not adjusted on a cold engine, prior to the compression test, those numbers have basically set the low end but do not really tell you the true compression values. RTFM, which says adjust valves immediately before compression test.

Great advice. I was worried that the manifold job would be tricky and likely difficult. I bought the gasket, that's when I learned that both manifolds were done at the same time.

During my second trip permit - legal driving on street - I needed to go to WA state for family issues, was making major money on a large job - more loose money than time - so I took it to my Vietnamese mechanic buddy's garage. He owns two 350SD , cut his teeth on Mercedes diesels in Vietnam, prevalent there. I know the guy is good, he found the stalling gremlin in my Chev van - I had searched for two years.

He adjusted the valves, he said two were close to tight. Also smoothed out the occasional hard shake at idle, not sure how that was accomplished. He said he tested the injectors and they were good. I could ask him for more details on that. So the compression test was done about 1600 miles after the valve adjustment. I was thinking that would be good enough but I'm still fairly new to some of this.

Glow plugs sounds like a good idea, not an expensive one either.

I think the odo is accurate, the car exibits modest wear and tear. Oregon DMV gave me the PO's Eugene address, I was in the area so I took the bold step of going to the door. The young woman who answered said the names on the title were her grandparents, both deceased - her mother, now in Montana was the one who had signed it over to the garage, didn't sell it, they told her it would cost $6K to get it running, she gave it to them to cover the diagnostic work. Sounds a wee bit crooked. They did have the title at one time.

Anyway, it had been her father's car, he was a VW mechanic, in her words: from the factory in Germany. It was her car for 15 years. When I got it there was too much tranny fluid in it, maybe a pint or more too much. Made me worry that various fluid issues might not have been dealt with well, after all the dad was getting old, maybe long gone, though you'd think she'd had good tutoring.

The acceleration is not good. I hemmed and hawed about buying it, I only did so because it's a cherry with low mileage. I think I'll land on my feet. If it had been sub 300, would have been forehead smack action, so I'm pleased that it's at least what it is.

It was a cold test, so what, would warm be maybe 20 psi higher?

I'll check the throttle linkage and alda.

I saw a vid from Kent saying that bad injectors can lower life - damage compression. Said that if they squirt instead of spray, still runs, but will wash oil off the cylinder walls.

My thought is that low mileage doesn't necessarily mean all components are in great shape. I did the math, 10 miles a day, every day would yield about 135K. Every start up is going to give some wear and tear. Pretty sure that highway mileage will still make for wear and tear but of course the conventional wisdom is that highway miles are less wear and tear than city miles. I think it spent it's entire life in Eugene, not a huge town, no salted roads. So a 10 mile a day average is not unreasonable.

I've not checked comprssion on my SDL. It has 350K, we occasionally have early mornings around here in the high 30s, never any difficulty starting. Much better acceleration than the 300D. Better engine of course, but still. My 300SD was noticeably better than the 300D.

I think you've done very well, these are getting really hard to find in decent condition. Mechanicals can and will get sorted, it's the cosmetic stuff that will eat you alive if you want the car to really look nice.


I'm pretty sure the proper test is cold, done immediately after the valve adjustment, which must be done on a stone cold engine.



I recently fixed a sloppy throttle linkage on a '95 E300 I picked up last fall, added all sorts of power to the right foot. Still sorting other issues, like very poor power after cold start when temps are around freezing or lower.


My advice is always to start with simple / cheap attempts at fixes, and progress to expensive / complex. However, do not ignore what you know to be wrong, even if expensive / complex to fix.

No.

from the fsm: Measure compression pressure at 80C

link to it:
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/01-010.pdf


yes valve adjustment is done on a cold engine but why IMMEDIATELY ?

I'm tempted to do it again with the engine warm. Will need to move quickly. Not sure if there's a way around it but I had to partially dissasemble the throttle linkage mount to get the socket on the #3 injector, I think it was that one.

OTOH I read one account where a guy said he thought checking it cold had merit, as the engine is often cold when you start it. Certainly the starts you worry about with an aging diesel are when it's cold.

Not much point in checking the engine when it is warm if you are concerned with cold starts. It is a handy comparison aid when you are checking the over-all health of the engine regarding wear.

At 300+ PSI your problem isn't with compression. 275 is considered "minimal". I suggest you borrow another compression gauge to verify the results. I've had gauges lie to me before.

Thanks for that info, I stand corrected!


Compression values depend on proper operation of the valves. Loose valves can prevent a full charge of air (lower compression) and tight valves can allow some of the air charge to escape (lower compression). The test values in the FSM were established on the assumption that the valve clearances were properly set, so if the valve clearances are off, the test results are not valid. A stretched timing chain can also affect compression, that's why a good practice is to check the camshaft timing when the valve cover is off to perform the valve adjustment.



If there is carbon deposited on the valve face or seat, after an adjustment and some vigorous driving, those deposits will probably reduce or disappear, changing the valve clearance. Sometimes a neglected engine will need two or three valve adjustments in a shorter maintenance cycle, for instance 1000 miles between adjustments, until such deposits are gone and the clearances will stabilize a bit.

If the block heater is working, you can plug that in immediately after driving and before you check the compression, that will keep the engine temp up closer to 80 for a longer time.


The late Marshall Booth used to say the best compression test was cold start during winter. If the engine starts immediately and fires evenly on all cylinders, your compression is good. No need to spend time or money on a compression test which will only confirm that your engine is healthy.