Hello All-

After adjusting the valves to spec (1977 300d non-turbo) and doing a compression test, I received the following results:

1- 260
2- 260
3- zero
4- zero
5- 220

I was pretty disappointed in the results. I did this compression test cold, as the car would not start. The last time the car ran was about 3 months ago. During this time, I experienced a significant decrease in power. The next day, the glow plugs did not work, and I have been diagnosing problems since. I decided that the go/no go decision on fixing this car would be the results of the compression test. I know people usually do this test with a warm engine, but I did not have the luxury.

I am thinking that it may be:
1. Rings going bad, and thus losing compression.
2. Stuck Valves.
3. Bad head gasket (I would like to put my money on this, as the performance issue was more abrupt, and there are two cylinders affected, and not just one.

Is there anything else that may have caused this?

To fixing any one of these problems, I am obligated to pull the head off correct?

BTW, I used a compression tester from Harbor Freight. This was done through the injector holes, with head shields removed. (Injectors, BTW, overall, are covered with carbon, however the cleanest of the five were from the cylinders with zero compression...) I would love any input you might have.

Clean injectors on two adjacent cylinders with no compression is a strong indication of coolant getting into those cylinders and cleaning out the carbon hence a bad head gasket. Now many revolutions of the engine were you using to get those numbers?

How many miles on the engine?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

totally stuck closed rings would have significant low compression, but not zero... a blown head gasket would have significant low compression, but not zero... missing valve heads/broken valves would have zero compression... a hole in the pistons could show zero compression... although, the diesel compression tester, has a schrader valve that opens above a certain psi on the HF tester... possibly it needs higher pressure to reveal any pressure on the gauge... not sure...

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1987 190D 2.5Turbo
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1987 300TD
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I cranked the engine about 6-8 revolutions for each cylinder. There is only 150,000 miles on the car. It is older (77') but I have. Hanged the oil regularly since I have owned it. The HF tester may not register at low c

I did about 6-8 revolutions per cylinder. The car has about 150,000 on it which isn't a lot and I have changed the oil regularly since I took ownership. I am really not sure about the HF gauge but I suspect it could only open at a higher psi. It sounds like either way I am looking at removIng the head. The coolant sounds like it would make sense as there was a noticeable difference in the appearance of the injectors on the cylinders with no cOmpression.

There is another test but not really required. The head has to come off in my opinion. Gasket may have just corroded or deteriorated with age.

Head may still be flat. Not the worse senario in your situation as rather than being somewhat labour intensive it should not be expensive hopefully.

I'd throw out the schrader valve not opening below a certain psi theory. The should open with very low psi. On the cylinders with zero psi, crank with your finnger over the glow plug holes. You should feel zero pressure, otherwise you had a leak in your compression tester.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

If the zero compression is being caused from a head gasket leak into a cooling water jacket you MAY see some bubbles in the radiator while cranking the engine. A leakdown test though would tell you for sure what's what.

A head gasket leak into the cooling system big enough to cause zero compression would blow the cooling system to bits.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Ill link some ideas.
http://www.youtube.com/watch?v=tFcKOYXaTWM

So maybe a stuck valve then? I gues I could try and soak the cyl

In brake fluid or that Mystery oil to see if it changes anything re the rings, but I feel that is definitely not it.

If you were really measuring a true zero then you should not be able to feel anything sucking / flowing past your finger / hand whilst pressed up against the glow plug hole. (Er with all the glow plugs removed from the engine to help the starter and battery along)

I'd do this simple test first before zipping off for a leak down tester or pulling stuff to bits.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

What sort of fuel has it been run on?
Was there a lot of blow by?
As you have 2 low results next to each other it is most likely a blown head gasket.
Head removal is the only option.

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1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
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With zero compression the one thing that jumps out at me is did you adjust the valves correctly. It is free to check so maybe do this first. Loosen the valve adjusters on the low cylinders by quite a bit then re check for that matter loosen them all. if the results go up then they were too tight. I have been bit by this before. If the valves never close you will get no compression. Also Harbor Freight guages are crap I have one here that did not last through the first test , crapped out after 2 cylinders. Also you can get a bit of heat in the engine by plugging the block heater in for at least an hour , it won't be hot but it will be warm. Cheers Dan

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