Vibration increase, particularly at idle…any ideas?
 

Hi all,
I’ve noticed in the last few days that I’m feeling more vibration than usual at idle in my diesel 940.

Obviously the D24 isn’t the smoothest engine in the world anyway (as much as I love mine!) but it definitely feels a bit different to usual.

In the last couple of weeks I’ve done the following:

Changed from 10w40 semi synthetic to 5w40 fully synthetic

Fitted replacement rear box exhaust hanger rubbers (same size as the old disintegrating hoops, but the rectangular box style design)

Changed from 185/65/15 tyres to 195/65/15.

Obviously it’s unlikely that the tyres will have affected anything, but does anyone know if the oil change may have done? It was very happy on fully synth for the first week, and is still running well, just with the added vibrations.

Any advice most gratefully received!
Phil

I shouldn’t have thought the weight of the oil would make much difference. 5w-40 and 10w-40 are supposed to be the same weight once hot. The 5w oil should flow better when cold, but so long as it isn’t leaking out I shouldn’t have thought that would be a problem.

Were the old and new oils the same brand? Unless you somehow extracted all the 10w-40 you will now have a mixture of the two. They are probably, but not necessarily, compatible.

If it were me I’d check the exhaust first. Not only are they often the source of strange noises but it should be the easiest thing to examine.

I agree re the exhaust. It’s a long stainless system with just one box at the rear. As it’s only supported at the downpipe and the back box, it does tend to move a little, and I previously had issues with it rattling against the hoop style retainer that bolts to the bellhousing to support the downpipe. I sorted this by wrapping a length of exhaust webbing around the downpipe and clamping the retainer around that to damp the metal-on-metal vibration. It may be the case that the webbing has deteriorated and needs remaking…I’ll investigate!

Oil wise they weren’t the same brand but appear to be compatible. Both are specced to A3/B4 and VW 505-00. The car isn’t losing oil (it never seems to burn any, despite being just shy of 300k miles!) which was my primary concern with switching to 5w. Pressure comes up quickly and the car doesn’t appear to be down on power or ailing. I’ll likely do another change with the fully synthetic 2k in which should hopefully flush out the last of any remaining semi.

940tic auto 1995
 

hi phil
if the problem is not the exhaust put a post on the D24.com web site . they have some guys who specialise in this engine hopefully give you some pointers ,
there are guys on our 900 forum too so hope you get it sorted its really something i don't know about .

Early D24s had solid valve lifters and later cars had hydraulic lifters Phil, i'm not sure when they changed. My first thought would be one or more of the hydraulic lifters is "bleeding down" at idle due to the slightly thinner oil.

It's also possible the new oil has dislodged some dirt that was maintaining oil pressure in the suspect lifters and they are now a bit dirty and as such not operating fully at idle/lower oil pressures.

I'd be inclined to switch back to the 10W40 semi-synth and before you top up to the correct level, add ~0.5L synthetic ATF such as Carlube ATF-U, NAPA MVA or similar. This will help clean the hydraulic lifters if yours has them, clean the valves and piston rings to help prevent them sticking, revive the rubber seals in the engine etc. You could also have dirt in the fuel system causing a partial misfire at idle, try adding some of this, it's reputed to do a good job on diseasels :

https://www.halfords.com/motoring/en...ml-264671.html

Many moons ago i used some on my n/asp Ranger 2.5D (Ford-badged Mazda B2500) after an advisory on the MoT about it being smoky - cleaned the exhaust a treat, improved power and economy. Others on here have used it more recently in newer Volvos to geat effect as well.

Hydraulic lifters were introduced in 1993 with other service engine modifications ie different waterproof, added bet tensioner.egr,catalic converter.timing setup,different size cambelt ,plus few other changes

Could a sticking injector be the culprit?

Cracking injector pipes, looking for a change in "smoothness" may help. Revving it clears the problem.

When I had lorries, this was not uncommon. In the 940 diesel l had, the lovely engine always struck me as , a little truck engine!

Already suggested Andrew and the D24 was used by VW as a little truck engine. :thumbs_up:

Dave, we used to have an LT35 D24, back in the 80's. It was rubbish, we quickly replaced it with a lovely brand new Merc 307D!

Phil, why don't you post this in the diesel section of our forum, thats where I used to post when I had a D24Tic and thats the part of the forum where a lot of the knowledgeable D24T owners post

https://www.volvoforums.org.uk/forumdisplay.php?f=113

I never said they were any good Ellie! :tongwink: :laughing-smiley-018

As a truck engine, not much use but not so bad in cars.