NegevLandRover Posted April 24, 2009 Share Posted April 24, 2009 LR Defender 300 TDI. Did a 40'000 KM service - all oils and filters etc. Nothing out of the ordinary happened. Also put in a brand new Ali radiator, second hand intercooler, brake servo and pump and rear brake pads - all went well here too. Took the LR out for a whizz to see all was OK - no problems at all. Then started a longer drive - 20 kms down the road - engine temp fine, lotsa power (old intercooler was in a mess) and suddenly oil pressure light starts to glow dimly. Clutch in, free wheel down the highway and light becomes brighter, next exit just down the road so gently does it and light dims abit but stays there. Pressure unit is a after market one that is more sensative than orignal and comes on at 5 instead of 15 PSI so when the engine is hot if you are in neutral the light will come on - this way even during a long days work with engine on the whole time you get indications through out the day that the unit is working and if the pipes burst you get an earlier warning than you would with the original so the fact that the light came on was a heads up but still not a sign that all was lost. Crawl under LR and checked the unit was properly conected, no oil leaks, oil level correct, change the oil pressure unit. Get back in LR and start her up - all looks fine - open ignition light comes on, start up and in tick over light is on (as I said above this is normal with the unit I have), turn revs up and the light goes out. Back onto highway and a few kms down the road repaly of the whole scenario but much sooner than the first time (engine was warmer to begin with). Open the oil rad pipes and there seems to be very little oil in the rad but pipes are clear as is rad. Take out oil thermostat and it is jammed in the extended position (open - right ??) Put everything but the oil thermostst back in and re-start - everything is back to normal. Drive 180 kms and everything is fine. So what the hell was wrong ??? I presume that the oil thermostat works like the coolant one and when open allows the oil to course through the oil rad ?? Or is it one of these "normally open" systems - when the thermostat opens it actually closes one of the paths and sends the oil around the rad ?? OPTIONS Oil thermostat was the problem ? Air blockage in the oil rad/pipes ? (never heard of this before) GREMLINS ?? Opinions please. TIA Adam Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 24, 2009 Share Posted April 24, 2009 Pressure unit is a after market one that is more sensative than orignal and comes on at 5 instead of 15 PSI That's less sensitive - if it comes on at a higher pressure it is being more sensitive to any drop from normal pressure, rather than only coming on when the pressure drops to almost nothing. Quote Link to comment Share on other sites More sharing options...
NegevLandRover Posted April 24, 2009 Author Share Posted April 24, 2009 That's less sensitive - if it comes on at a higher pressure it is being more sensitive to any drop from normal pressure, rather than only coming on when the pressure drops to almost nothing. Silly me - I got it the wrong way round - LR standard comes on at 5 or less mine comes on at 15 or less. Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 24, 2009 Share Posted April 24, 2009 Theres something a bit wrong with your engine if your seeing less than 15psi at idle... I'd expect 5 bar when cold (75psi) and 2bar (30psi) when hot as a minimum... Quote Link to comment Share on other sites More sharing options...
western Posted April 24, 2009 Share Posted April 24, 2009 300Tdi manual says oil pressure with engine at normal operating temperature 1.76 to 3.87 kgfcm3 or 25 to 55 psi. Quote Link to comment Share on other sites More sharing options...
NegevLandRover Posted April 24, 2009 Author Share Posted April 24, 2009 Soory guys - should have written BAR and not PSI - so pressures are correct. Can some one explain to me what happens when the oil thermostat opens/closes and if this migh have been the problem. Taking it out solved the problem - or circumstance did. Adam Quote Link to comment Share on other sites More sharing options...
western Posted April 24, 2009 Share Posted April 24, 2009 IIRC when it opens it allows oil to flow from the oil cooler back into the engine/oil pump. Quote Link to comment Share on other sites More sharing options...
Rich_P Posted April 24, 2009 Share Posted April 24, 2009 IIRC when it opens it allows oil to flow from the oil cooler back into the engine/oil pump. To prevent overcooling of the oil, allowing to keep the engine at operating temp? Quote Link to comment Share on other sites More sharing options...
NegevLandRover Posted April 25, 2009 Author Share Posted April 25, 2009 Yeah - I know what it is there for but I don't know the system well enough to know whether the system is "normally open" or "normally closed". I am trying to figure out why if it was stuck in "open" it caused the problem ?? Quote Link to comment Share on other sites More sharing options...
steve_d Posted April 25, 2009 Share Posted April 25, 2009 Open or closed it should not change the oil pressure. Is the cooler and stat something that has been added? They should be plumbed so that oil (under pressure) comes from the pump into the stat, out to the cooler, back to the stat, and then into the oil galleries still under pressure. If it has been wrongly plumbed it may be taking oil (under pressure) from the pump and passing it through the stat and cooler and back to the sump. This would be why you loose pressure when the stat opens. Steve Quote Link to comment Share on other sites More sharing options...
NegevLandRover Posted April 25, 2009 Author Share Posted April 25, 2009 Open or closed it should not change the oil pressure.Is the cooler and stat something that has been added? They should be plumbed so that oil (under pressure) comes from the pump into the stat, out to the cooler, back to the stat, and then into the oil galleries still under pressure. If it has been wrongly plumbed it may be taking oil (under pressure) from the pump and passing it through the stat and cooler and back to the sump. This would be why you loose pressure when the stat opens. Steve Nothing added - the 300 TDI comes with the oil rad as standard. The plumbing was not touched save for the swapping out the oil rad along with the coolant rad and there were no mistakes made in the process. Adam Quote Link to comment Share on other sites More sharing options...
western Posted April 25, 2009 Share Posted April 25, 2009 probably a faulty oil pressure sender. Quote Link to comment Share on other sites More sharing options...
NegevLandRover Posted April 26, 2009 Author Share Posted April 26, 2009 probably a faulty oil pressure sender. No - as i said, we changed the oil pressure sender and the brand new one acted exactly the same. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted April 26, 2009 Share Posted April 26, 2009 Sorry, not being funny, but I'm not following the operating pressures here. You say the LR switch activates at 5 bar and yours at 15 bar, yet the operating pressures of the engine are 2 - 5 bar. To my knowledge, the TDi doesn't have an oil stat, just an oil cooler in the rad. Is this a version for hot climates? Can you post up a photo? Quote Link to comment Share on other sites More sharing options...
western Posted April 26, 2009 Share Posted April 26, 2009 all Tdi's have a oil stat [it lives wihin the oil filter head]& the oil cooler within the radiator side tank. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted April 26, 2009 Share Posted April 26, 2009 As usual I stand corrected. That isn't something I knew despite owning one for 4 years! Quote Link to comment Share on other sites More sharing options...
western Posted April 26, 2009 Share Posted April 26, 2009 As usual I stand corrected. That isn't something I knew despite owning one for 4 years! follow the oil cooler hoses back to the filter head, one connects to a top hat type part on the side of the fliter head the oil stat [called a waxstat] lives inside with a spring & washer, maybe Negev's spring is missing or tired & needs replacing. Quote Link to comment Share on other sites More sharing options...
steve_d Posted April 26, 2009 Share Posted April 26, 2009 follow the oil cooler hoses back to the filter head, one connects to a top hat type part on the side of the fliter head the oil stat [called a waxstat] lives inside with a spring & washer,maybe Negev's spring is missing or tired & needs replacing. OK we're all learning something here but I'm still confused. No matter whether the oil stat was open, closed or non existent it cannot produce a low oil pressure. The oil is either staying in the engine or going round the cooler but will still be under pressure no matter which. Steve Quote Link to comment Share on other sites More sharing options...
western Posted April 26, 2009 Share Posted April 26, 2009 only other thing to check/replace is the oil pump, it's only the pump that moves the oil around & pressurises it, OK the moving engine internal components also give it a good squeeze to. Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 26, 2009 Share Posted April 26, 2009 If you overcool the oil the viscosity increases, and thicker oil will generate higher oil pressure... This is why you usually see well over 5 bar at cold idle dropping to 2-3bar when its hot. This would indicate that cooling the oil (ie making it thicker) has increased the oil pressure, which makes me think there is an issue with the engine internals. Either the oil pump is worn, the pickup gauze is blocked, or some of the bearings/shells arent right, causing the pressure to drop. Your pressure sensor isnt going to be 15 bar. your original 5 and 15psi values sounded correct to me. Most cars seem to have a sensor in the region of 3-5psi (i've never understood this as it basically means if the light does come on your engines humped!), and 15psi seems like a common upgrade, although some cars such as our A4 come with a 15psi sensor from the factory. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted April 27, 2009 Share Posted April 27, 2009 This seems to be going round in circles but I'll throw in my experience. On my 2.5NAD (no thermostat, no oil cooler, different system) the standard oil pressure switch would make the oil light glow dimly after the engine had been worked very hard and then brought down to tickover. The engine had 150k miles; my understanding was that the oil got thinner at high temps and the pressure was lowest at tickover (when the oil pump was spinning slowest). The combination of a worn engine and worn pump conspired to bring the light on, but the light would go out as soon as the revs were lifted off tickover. It didn't seem to damage the engine - it ran for another few thousand miles (and then stopped quickly, in a river, full of water...) Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 27, 2009 Share Posted April 27, 2009 Turbo: Yep thats my point, thin (hot) oil gives lower oil pressure, however the engine is designed such that at idle the pressure is over 25psi from the numbers western posted. If its dropping below this when hot then there is something wrong with it. Running the oil colder (by removing the stat in the oil cooler) will appear to "cure" the issue, but this is simply because the oil is thicker at lower temperatures and naturally gives higher pressure as a result. Quote Link to comment Share on other sites More sharing options...
steve_d Posted April 27, 2009 Share Posted April 27, 2009 Turbo: Yep thats my point, thin (hot) oil gives lower oil pressure, however the engine is designed such that at idle the pressure is over 25psi from the numbers western posted. If its dropping below this when hot then there is something wrong with it. Running the oil colder (by removing the stat in the oil cooler) will appear to "cure" the issue, but this is simply because the oil is thicker at lower temperatures and naturally gives higher pressure as a result. Whilst I agree you will see a change in pressure from a cold engine to a hot one I doubt the change in temp from before the cooler to after the cooler will show much difference at all. It is cooling the oil not chilling it. Steve Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 27, 2009 Share Posted April 27, 2009 i dont expect to see a pressure difference across the cooler itself.... What i mean is that if with the thermostat fitted the engine oil is kept at 90c and without it its only getting to say 60c, then removing the stat will have made the oil thicker, and as a result raised the pressure. Quote Link to comment Share on other sites More sharing options...
steve_d Posted April 28, 2009 Share Posted April 28, 2009 i dont expect to see a pressure difference across the cooler itself....What i mean is that if with the thermostat fitted the engine oil is kept at 90c and without it its only getting to say 60c, then removing the stat will have made the oil thicker, and as a result raised the pressure. Sorry, not quite what I meant. I'm saying you will see a difference in pressure from a cold or hot engine but not see a difference between the cooled or not cooled oil. The cooler will reduce the oils temperature but not by a huge amount. Steve Quote Link to comment Share on other sites More sharing options...
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