Thread: oil light flickering

Hi Guy,

As per the similar thread currently doing the rounds on this Forum, you would be well advised to get your 200Tdi to a mechanic quick-smart and have an oil pressure gauge temporarily fitted to see what the actual pressure is.

At 300K km, things must be expected to be wearing out. Might be just an on-the-way-out pressure switch but it might be a well-worn oil pump or failing pressure relief valve. If it's the latter, it won't get any better and will eventually kill the engine if the pressure continues to fall.

About I week ago I witnessed a famous spanner-wielder (initials JC) who frequents this forum check out a Td5 with similar symptoms. The workshop gauge confirmed the switch was telling the truth - very low pressure at idle.

First suspect was the infamous oil pump bolt but after the sump was off the bolt was found to be firm (just, and no sign of Locktite). Next the relief valve was checked. The spring was intact but The Guru thought he could see something wedged in the valve plunger. When it was pulled out, a fragment of die-cast metal fell out - presumably a tiny part of the original pump body casting that had been waiting to cause mayhem since the vehicle left the factory. If the owner had ignored the oil lamp flickering on at idle, his very expensive Td5 engine may well have expired prematurely.

Ian

The immediate cause is that the oil pressure is below the switch-off pressure of the sender - but I don't imagine that this is the answer you are looking for.

There are a number of factors that will give this result, and the answer is probably a combination of them.

1. hot oil with reduced viscosity
2. Clearances have increased with engine wear so for a given oil viscosity pressure is less at a given rpm - both effect of wear on the pump and on the bearings
3. Pressure drop across the filter increases as the mileage increases since the filter change.
4. Some of the oil molecules break up, reducing oil viscosity for a given temperature
5. Oil temperature is higher because of scale on the oil cooler and reduced cooling efficiency due to other components ageing.
6. Idling speed slightly down from spec perhaps
7. Switch-off pressure of sender is likely to have increased slightly due to wear on contacts.

Probably a few others I can't think of. Items 3&4 are reset at each oil change, which is why it takes a few thousand kilometres to start doing it again. My view would be that there is nothing to worry about, just an indication that the engine is showing some signs of wear and age.

John

Just reviving this thread (after searching) -

We don't know how the original poster got on, but my 300tdi at 220000km is doing the same thing - oil light flickering at idle when hot (but not overheated). JD's points in post#3 are logical and I'm wondering what steps other tdi users have taken to rectify the problem.

The oil pump is a bugger to get at and as I've replaced the timing belt recently I'm reluctant to go straight to the oil pump if something as simple as an oil light sender/switch replacement can settle the issue.

Views, experiences and thoughts welcome......

The first thing I would check is the oil pressure switch. It is cheap, quick and easy to determine if that is the problem.

Three times on three different vehicles in the last 50 years I have had an oil light flicker on idle when the engine warmed up. In each case it was just the switch that was failing. The most recent incident was the Defender, about a year ago.

pull the lead off the switch, if its oily the switch is stuffed.

Originally Posted by Blknight.aus

pull the lead off the switch, if its oily the switch is stuffed.

Thanks Dave, I had looked at that and there's no oil seeping through...

I'll have a replacement sender tomorrow and I'll try it.

Most of my experience with diesels and oil lights flickering on tick over. Which I happen to add my new 200tdi disco does too. I that it is crank case pressure

I am taking it that mine is crank case pressure. Caused by worn values, rings or something along those lines.

To check this start the engine and take of the oil filler. If is chugging like Thomas the tank engine then there your problem. The other way is when it is running take out the dipstick. If it covers you in oil then you have crank case pressure.

This will also cause oil leaks as there pressure in the engine is finding ways to get out of the engine. A defender I had a few years or so ago did this and ended up blowing oil out the rear main oil seal.
BTW all the time through this is did not blow blue smoke or show any other signs of bracketed rings or values hence why I do not look here first.

Ali

or check the crankcase breather gear for blockage.