I drove my Defender (300TDI) 45 miles (90 miles total) for the first time on Friday and then Sunday for the first time in about 7 month. As always, it starts first time on the initial turn of the key. It drove lovely on both journeys averaging around 55/60 Mph on the motorway, though could go faster if needed. Whenever I got to an upward gradient, I appeared lose speed, for example, traveling at 60mph on flat road, as soon as I began to climb a gradient, for example 15/20% my speed would gradually reduce to around 50mph. However, it’s done this for years and I’ve often planned setting the valve clearance, but have never got around to it because of I’ll health. I have always managed any shortfall in speed by preempting a gear change down to reduce the accelerator depression. So pretty much all normal so far. However, on the return Journey, 2 mile from home in terribly wet conditions my oil light began to flicker and then fully illuminated. As soon as I got home, I turned the engine off and allowed it to cool for 10 minutes before checking the dipstick. The oil was obviously hot, thin and showing just below minimum. I checked the coolant and there was no water loss, no gunge and adequately pressurised. Again there was no water in the oil. The next morning when the lands was stone cold, I checked everything again. As expected the oil was showing more, infant it was spot on the max indicator on the dip stick. The oils was pretty dark, though not excessively. Again there was no oil in the water and no water in the oil. I started her up and the light went straight of and then began to fligcker again after about 2seconds. I lasted changed the oil and filter around 1200 miles ago (18 month), along with the fuel filter and lift pump. From what I can tell, there is no play in the turbo and no obvious sign of oil. I know I have a slight oil leak on the crank seal, though I’ve had this for years. It drives nicely with no excessive knocks, apart from a slight knock from the air filter housing where the bracket has snapped. There is plenty of torque and the old girl is responsive. I’ve never been one for driving it to her to her top speed, my bones couldn’t cope with the rattle lol. During the drive there was no sign of over heating with the gauge showing almost halfway between cold and the middle mark. Only briefly did it move uptowards the middle on longish run up a 30% gradient, but quickly came down afterwards.

Has anyone any suggestions for what the problem could be. I’m hoping it’s only the switch or sticky valve spring. I’m hoping it’s not the oil pump or a worn engine. There momentarily spiking at startup as expected, but quick disperses with a swift press of the accelerator. There is no smoke under load. It has approximately 120000 on the clock. The timing belt was changed about 7000 miles ago.

I was hoping it was a faulty switch and have ordered a new OME one along with a filter as they were leader expensive. But, my understanding of the switch is that if it was faulty, then it just wouldn’t illuminate, my issues is that it is illuminating!! ‍

I use Halfords 15/40 part synthetic oil. I don’t have an oil pressure tester.

Anybody got an idea what might be the problem!!! Seriously, why do we keep doing this‍‍

You can test the switch if you have a multimeter, that would be my first port of call. Test it with both engine off and engine running.

while it is a good idea to have a pressure tester, my other supect would be the oil thermosthat in your filter adapter.

http://new.lrcat.com/#!/1231/29584/30331/2327/30616 nº 2. it might also be full of gunk. then if that is not the culprit get into the dirty stuff and do your oil sprinklers

I might be way off the mark but is it sounding like its hunting fuel?

fuel wise I would’ve expected consistent poor performance. It’s always got more and appears responsive to accelerator input. The loss of speed I was thinking was maybe down to poor valve settings, well I was hoping so!!

Switch wise, I’ve ordered a new one, so I will test both. I must say though, I always assumed a faulty switch would’ve resulted in the warning light failing to illuminate.

Thermostat in filler adapters is a great call, I would never have thought of that. What would cause that to fail and what would the symptoms be?

As always, thanks guys.

Landyfox said:

Switch wise, I’ve ordered a new one, so I will test both. I must say though, I always assumed a faulty switch would’ve resulted in the warning light failing to illuminate.

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It wouldn't be much use if that were the case. It depends though, I would have thought this switch would be normally closed? If its starting to corrode and seize up inside it wont open correctly when the engine is started, or there wont be enough oil pressure to open it, but the first instance is easier to diagnose with just a multimeter. Saying that the correct way is to use controlled air pressure on the bench to operate the switch but if you can get something into the bottom of it to try and do it by hand you should be able to feel any undue resistance .

I hope you’re right, that would be a nice quick fix lol

SWMBO had the flickering oil light on her 300Tdi ..... and ignored it .... .....

Then it came on just as she was parking up in her works car park....

The flickering was, we assume an indication of the switch failing ..... the light coming on and staying on was definitely the switch failing .... I know this as when it failed ..... the little darling burst, & let a good quantity of oil out, spraying that side of the engine and bay with it - what a f'ing mess ( understatement).

Mr AA was very helpful, and used his entire stock of paper towels so we could see the engine again, and I fitted a gauge, topped the oil up, started it up, ..... and the oil pressure was fine ..... got a new switch and Bob is my mothers brother.... no problems since .... but ... if the switch had burst at any speed, I think the outcome might have been somewhat different

My 19J switch worked loose a few years ago at 30mph, BMW behind me had to put its wipers on!

I never realised that the switch could cause so much mess. Though it stands to reason when the engine is running and fully pressurised!

Well if it’s only a faulty switch I will be delighted

Oil lights have a habit of coming on when the damage is already done so if it's been driven with the light flickering then I'll do a +1 on poorly switch too

What’s A..?

I was rather hoping it would be the engine as there was no loss in performance.

Landyfox said:

What’s A..?

I was rather hoping it would be the engine as there was no loss in performance.

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Low oil pressure might not do any damage, no oil pressure however will. The old fronteras for instance, the petrol ones were rebound for it but they ran fine. The proper way to diagnose this is an oil pressure test but as you don't have the kit to do this just replace the switch and see, but drive it easy until you do.

nobber I ordered a pressure testing kit anyhow as I thought it would be a useful addition to my toolbox. The last thing I want is for the engine to bugger up. I’ve no means to remove the engine and strip it down. Everything I do on it, is done with the engine in situ.

Just a quick question, when testing the oil pressure, what’s the best method? I was planning to first record the pressure immediately after startup and the 10 minutes later once the engine has warmed up. When I remove the oil switch, I’m assuming I won’t loose too much oil as the engine will be turned off and no pressure.

Remove switch and put the test kit where the switch goes, run it cold, you can let it warm if you want but you will soon know if the pressure isn't within spec.

nobber said:

Remove switch and put the test kit where the switch goes, run it cold, you can let it warm if you want but you will soon know if the pressure isn't within spec.

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Thanks nobber

One thing sounds very strange to me.

Dipping your oil 10 mins after a run it was below min, then the next morning cold it was max. Have I missed something?

K14 said:

One thing sounds very strange to me.

Dipping your oil 10 mins after a run it was below min, then the next morning cold it was max. Have I missed something?

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No you are almost right. Approximately 5-10 mins after the run, it was solid just above the minimum mark, though the dip stick was splattered. I dipped it 3 times. Then later when the engine was completely cold, I dipped it two more times and it sat just under the max mark.

If you have no reason to believe you have a low oil pressure fault (oil level normal etc) then I would fit a new pressure switch and take it from there.
Oil pressure switches etc are all made and wired fail safe. So an oil light is either a low pressure fault, or a switch/ wiring fault.