Topped up my oil yesterday as it was a little low. I've done around 100 miles since then.

As I was parking up this evening I noticed my oil pressure light flicking on an off every few seconds.

Parked up, let the oil settle and checked the dipstick.

It was right on the bottom marker. I topped it up again, around half a litre I guess.

I then pulled out the spark plugs to see if it's been burning it. They're all a light greyish colour with no visible erosion anywhere. As they were out I put my new ones in to see if my slight hiccup on LPG goes away. Once they were I started it up and had my assistant gently rev the engine while I checked the exhaust - all fine there.

So, I'm confident it's not burning it in large quantities bit there's no evidence of a major leak anywhere either!

Nothing dripping off the engine, rocker cover gaskets were nice and dry when I was changing the plugs. The coolant in the header tank is a nice red colour.

Any ideas on where that much oil could go that quickly?

Ok, so I've done around 25 miles and I'm getting the light coming on at idle again.

If I rev the engine it goes away and if I put it in neutral it goes away, as the revs rise slightly.

I checked the oil level at a petrol station and it's around the max line. The handle of the dipstick was wet though, I've never noticed it being wet before. The bit of kitchen roll I keep under the bonnet is also damp, which I've also never noticed before. That lives between the EAS box and AC pipes. I've no idea if this dampness is related to my oil pressure issue though.

Headed off to work as I wasn't far away and borrowed a rubber glove to tie around the header tank filler hole. Ran the engine and it doesn't seem to be pressurising.

Checked the oil again and the level seems to be OK and the oil doesn't seem to be mixing with coolant. I was wondering if the head gasket had gone, letting coolant in to the oil and thinning it out.

The guys at work think it's the oil pressure sensor/switch.

Does this seem reasonable in you experience(s)? I feel unconvinced but that might just be me being over-worried about it. I can really do without a serious engine issue!

Changing the pressure switch would be the simplest thing to try first I think - if it still flickers at idle... then its probably indicative of actual low pressure.... which can't be a good thing :(

Seen a couple of anecdotal posts on the facebook groups of others that have had a faulty pressure switch cause the flicker. Fingers crossed that's all it is!

So, before I order one - did they change the sensor when they went from GEMS to Thor?

Seems to be two part numbers. STC4104 and NUC100280L.

I think NUC100280L is the one I want.

Yes, NUC100280L is the correct part number - I just checked on my spreadsheet of engine parts that I made when I rebuilt a new Thor engine a few years ago.

If that doesn't sort it, then it could be oil pump gears - they are known to crack over time - one of the spare front covers I bought to recondition (again for the replacement engine) had a cracked outer gear when I took it apart.. made me thankful I was putting new parts in!

It isn't the worst job in the world to do it, as it doesn't require a total strip down of the engine - just the front cover to come off, but still probably a weekend's job to do.

Ah, the front cover. The front cover and I are great friends - I had that off a couple of weeks after buying the car.

The gasket split and spat all the coolant out of the top passenger side corner.

I'll price up a pump and a switch. I'm guessing the pump is one to not penny pinch on but is there any reason to avoid the cheaper pressure switches?

Called LR today and they £38 for one. It's not bank breaking but I can see others around for anywhere between £2.50 and £15!

I'm guessing it's the same switch that's been in use on these engines for decades and plenty of people have copied by now.

Sounds like a good excuse to get the timing chain swapped as well. It was looking a little slack when I was in there last and it's done another nearly 40k since then.

If I'm delving in there again might as well do the oil pump, timing chain and fit an oil pressure gauge in place of the standard switch. I have an empty space in my dash board where my factory radio used to be. I'm now thinking it's a great place to fit oil pressure and water temp gauges. I know I have a temp gauge on the dash but it doesn't actually tell me what the temperature is, only when it's too hot.

Does anyone know the thread of the oil pressure switch? Is it 1/2 UNF?

Did an oil change last night and went from 5W-30 to 10W-40 but it's still doing it.

Sounding like the oil pump?

I believe I bought mine from either Island 4x4 or LR Direct. I think the Island 4x4 one is Britpart - so I might have gone for the intermotor or allmakes one on LR Direct. They don't usually have a record of failing - the earlier version was known to blow the center out of the switch and piss oil everywhere (had that on one of mine back in NZ - scary stuff when you're miles from home!)

If it's still doing it after a change to thicker/heavier weight oil, then to me it sounds most likely to be the oil pump - I could be wrong, but even if you get in there and find it's something else - replacing the oil pump gears isn't going to hurt anything. It also gives you a chance to check the pressure relief valves and the likes.

I wouldn't skimp on oil pump gears, no - I think I got mine from V8 Tuner - though that was years ago. V8 Tuner Oil Pump Gears Though you may be able to get a decent set cheaper elsewhere - I'd avoid blue-box on these... Just had a look and Island 4x4 shows a UK Made OEM version at £45 + VAT, so not much in it.

I can't remember the thread on the oil pressure switch - but also from memory on the Thor font cover at least, there is an unused port which has a bung in it, which you might be able to use for the pressure gauge...

Alternatively do it how it used to be done in the old days, Fit a Tee into the hole with the pressure switch screwed into one leg and the capilliary tube for the gauge into the other.

I'll sit and price up parts tonight. Will do the pump gears, timing chain (do the sprockets on the cam/crank shafts wear out and need replacing too?) and the oil pressure sensor just to be sure.

I'll also get in touch with the place that fixed the gearbox in the Freelander and see what they'd quote for it. Bit tight on on time at the moment :(

As for fitting a pressure gauge, this looks like the t-piece you mentioned: http://www.mattlewisracing.co.uk/product.php/855/42/gauge_adaptor___matt_lewis_racing

Just need to confirm what size the thread on the Thor pressure sensor is.

Just knocking up a parts list using RAVE as a guide. It says I need to remove the gearbox oil cooler pipes and refit them with new O-Rings, presumably to improve access.

Would number 8 on this page be what I need? http://new.lrcat.com/#!/1234/91427/91612/7252/91708

The diagram looks to be different to the one in RAVE. In RAVE both pipes connect on the side edge of the cooler but in LRCat one is on the front.