Club 80-90 Forums

I've got an intermittent issue on my normally aspirated diesel 1.9 1Y engine from a golf, where suddenly it will start running unevenly at higher revs and will be down on power (often ending up having to limp along at 30 mph) If I floor it, the speed doesn't increase, but I get a cloud of white smoke until I decrease the revs. If I switch the engine off and leave it for 20 minutes or so, it often starts back up and runs completely normally for a while - including a 100 mile motorway run cruising at 55 -60, with steep inclines etc., fully loaded camper, 3 bikes, food, gas, water tank and family through the pyrenees from france to spain, without this cropping up at all.

OK, a confession, which may be a coincidence, or related: I usually use 15/40 diesel mineral oil, but have been topping it up with 20/50 mineral oil, as the engine has been using a lot of oil (although usually no smoke at all, and no visible leaks), so I figured as it is probably a fairly worn engine and the 20/50 might slow down the oil consumption. I've now topped it up with about 3 litres over the period of a few weeks and a few hundred miles, so the mix is probably mostly 20/50 now. The "episodes" seem to occur after i've topped it up. Could this be the cause? - some oil flow restriction or something that the more viscous oil is making worse? Shouldn't have mixed the oils? I'm planning on doing an oil change in the next couple of days back to 15/40 to help rule it out.

Any other suggestions of mechanical issues that may have these symptoms welcome, as I may have to be speaking to french mechanics in the coming days!

Crikey, that sounds a tough one to nail down.

My only suggestion is it could possibly be fuel starvation related? Have you ran the tank down to empty recently? Have you drained the fuel filter of water (or whatever it's called)?

Could be dirt in the lines or you could just need to change the filter.

I suspect the oil is a red herring.

Good luck,

Ringo

It may not be a red herring, it could be a pink one!
As it is coinciding with topping up could it be overfilling? Are the dipstick marks correct? Overfilling can lead to all sorts of weird things happening.

As Ringo said...the oil sounds like a red herring although I'm wondering whether you may have a breather issue and crankcase compression is throwing some of that oil up into the air filter, hmmm. Blocked air filter? but then it's not permanent.
Massive amounts of oil being drawn into the engine (valve stem seals) although not as obvious as worn rings/bores.
Either way...you do have a oil consumption issue. 3Litres in a few hundred miles is mad!!.

Martin

Overfilling can lead to excessive consumption. Aeration of the oil can lead to lack of lubrication leading to seizure of moving parts. It will also slow down the crank as it will now be running in the oil. You will also reach a point where the aerated oil is now being compressed by the descending piston which will slow the engine more. The statement that the engine then runs normally again after having been rested also supports an excess of oil theory.

Thanks for your replies guys - I have a custom dipstick which was calibrated during an oil change at 3.5 litres for low level, 4.5 for high level, but I have to say that I never get the same reading twice! Possibly as the dipstick goes over vertical as you draw it out so i've seen oil run up the dipstick just before i've read it.

I will check for overfilling, and may let some out, to help rule that out.

Other factors - I filled up with diesel at a spanish petrol station the day before it first happened. The last time it happened the fuel was pretty low (my fuel gauge is too random to truly work out how low). I've stuck in 30 litres of french diesel yesterday, so if it was dirty fuel, that will hopefully dilute it. Or make it dirtier

I can't see any dirt running through the fuel line, but there are air(?) bubbles going through, is that normal? I'll read up on draining the fuel filter - haven't done that before.

I checked the air filter yesterday, a few dead flies, but that was about it.

On the top of the fuel filter is a bolt that appears to do nothing - loosen this (this allows air in) and then loosen the drain at the bottom of the filter. Any water that has settled in the filter will then drip out. (this may or may not happen if there is a blockage in either orifice) Don't forget to re-tighten them both.
May be worth you checking the dipstick calibration as you are planning on an oil change anyway. 4.3 litres with a filter change on a 1Y according to Haynes.

Thanks, will try this now..

OK, an update. This isn't an intermittent problem anymore

Struggling to drive it anywhere, so we are currently stranded on a campsite (there are worse places to be stranded) in the Aquitaine region.

My neighbour on the campsite just happens to be a syncro owner with a bit of english and we have tried a few things - he seems concerned about the air bubbles running through the fuel line - there is a tiny split in the fuel line where it attaches the fuel pump - no fuel leaking out, but we've gaffer taped it anyway. Checked the air filter again and ran the engine without the air filter out to see it made any difference. There are still air bubbles running into the pump when running, and back again when the engine is stopped.

I bled the fuel filter yesterday, bit of water then clean diesel flowing out. Also let out about a litre of oil, which puts it at the low oil mark on the self-calibrated dipstick, where I would expect it to be. I'm sure i'm not overfilling it - the excessive oil consumption is a mystery and may be related, or unrelated, but i'm only keeping it within the acceptable range we calibrated on the dipstick. Painful 5 mile drive to the beach and back at 20mph.

I'll be putting in a breakdown call today, but one last description of the symptoms, in case any more ideas:-

From cold, starts and idles fine - out of gear if you put the throttle down it will reach high revs but after a couple of seconds, misfires and lots of white smoke. I took it for a test run this morning after the gaffer tape experiment - ran well for about a minute (oh the false hope!), got up to about 40mph, then sudden loss of power, juddering and gradually losing speed, pulled over and the idling was lumpy and it stalled. Restarted OK and juddered back to the campsite at 20mph using low revs.

It seems to me that this is a fuel or air starvation issue - the fact that it starts and idles smoothly encourages me that nothing is seized..

Because I can't drive it far, I haven't risked trying to find a garage to pick up a new fuel filter, oil etc. so fingers crossed the breakdown guy has some ideas.

I would certainly replace that fuel line - air getting in would cause your symptoms. Fuel wouldn't leak out - it is on the suction side of things but air can be sucked in. After replacing the fuel line I would bleed through to the injectors to remove the air that seems to be causing the problem. Gaffer tape is only a possible get you home remedy - replace the fuel line.

Breakdown guy was clueless, although there were communication issues with me knowing virtually no french, and him knowing no English. I pointed out the fuel line and wrote some stuff up using google translate for him to pass on to the local garage where it has just been towed. I fear we might not see it again - sleeping in a tent tonight if it doesn't come back, which is highly likely...

So after a night sleeping through a thunderstorm in a tent with no groundsheet above an ants nest (wife and son luckily tucked away in a decent 2 man tent loaned by our dutch syncro-owning campsite neighbours), I was reunited with my bus - a section of fuel line has been replaced (or possibly just wrapped with a larger diameter pipe), and the system "refilled" and runs fine again, 20 miles if test run later.

Thanks for the help and suggestions guys! The holiday continues, and the wife doesn't force me to sell the van!

i'll replace the line when back in the uk, once I've learned how to bleed/ refill the system. I'll be keeping that replacement bit of line in my spares kit...

If one section of fuel hose has failed the rest cannot be far behind - I would replace all of the fuel lines then you know that you are good for a few more years.
Now you can sit back and relax again!

There are two types of fuel filters for diesel engined T25s early&late .The late has a thermostat valve for the fuel return into the filter often they leak air into the filter.I replaced mine for a early one which has no valve.Often the cause of bubbles in the fuel pump supply hose is due to this faulty valve.

I can see air in my fuel line from filter to pump, I get a surging when going up steep hills at low speeds 2nd/3rd gear.
I`m thinking this could be my problem also. I was thinking of replacing the whole fuel line but if it could be the fuel filter I`ll replace that with an early type. Mine has the spin off filter on an `86 Jx.
BTW is the Fuel Line *mm internal dia all along from tank to pump or does it change?