Low oil presure when hot

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chris-the-gerbil

Well-Known Member
Posts
994
Location
Leeds
So after a trip back from the Carpathians I have an oil pressure issue....

Car is a 96 300tdi Auto D1. New radiator fitted, cleaned out the autobox rad (not sure that's relevant but...) and has the original pressure sender as far as I know. Engine has 160,000 on it, bottom end never touched and as far as I know it's had a reasonably hard life.

Oil pressure goes out more or less instantly on engine start (within a second). Sounds good, no problems or nasty knocks.

Running 10W40 semi synth oil which by the time this happened had been in perhaps 5000 miles for the roadtrip.

So..... climbing up a steep and I mean steep 20% mountain pass near the top the oil light is on at idle. Flickeringly so, to more or less all the time. This is after hauling it's fat backside, 3 people and a full load of camping kit all the way up a 2km high mountain - we topped out at about 2200m and the last 5km was more or less constant switchbacks. Rad temperature never moved from it's normal halfway position, as far as I can tell the viscous clutch didn't grab the fan so it was just idling round.

Soon as you give it a whiff of throttle the oil light goes out. after five minutes of standing, it's cooled down and the light is out at idle.

So... what to do? I'm tending towards dropping the sump at next service which is basically now and swapping all the big end shells. Is this worth doing? Is it worth trying to swap the mains too (and is that possible with the crank in situ - one of the end ones looks impossible to access unless the box is off..)

Or could it just be a old tired pressure switch? Checked the wire for chafing it's not that....

Assuming I drop the sump off, what else is there to look at? Pressure relief switch on the oil pump a good idea to service? There is a temperature sensor on the oil gallery as well I presume to send oil through that cooler on the right side of the rad? Don't know much about that.... comments would be welcomes....
 
I would check the oil pressure first.

I have had an oil pressure switch fail, but it failed 100%. Which is why I got a pressure gauge kit to check the state of the engine.

Cheers
 
Well that's the next question - I don't have a pressure gauge. Anyone recommend a decent electric sender one that can be plumbed into the cabin so I can see a decent number rather than an light telling me I've already wrecked the engine?
 
chris-the-gerbil said:
So after a trip back from the Carpathians I have an oil pressure issue....

Car is a 96 300tdi Auto D1. New radiator fitted, cleaned out the autobox rad (not sure that's relevant but...) and has the original pressure sender as far as I know. Engine has 160,000 on it, bottom end never touched and as far as I know it's had a reasonably hard life.

Oil pressure goes out more or less instantly on engine start (within a second). Sounds good, no problems or nasty knocks.

Running 10W40 semi synth oil which by the time this happened had been in perhaps 5000 miles for the roadtrip.

So..... climbing up a steep and I mean steep 20% mountain pass near the top the oil light is on at idle. Flickeringly so, to more or less all the time. This is after hauling it's fat backside, 3 people and a full load of camping kit all the way up a 2km high mountain - we topped out at about 2200m and the last 5km was more or less constant switchbacks. Rad temperature never moved from it's normal halfway position, as far as I can tell the viscous clutch didn't grab the fan so it was just idling round.

Soon as you give it a whiff of throttle the oil light goes out. after five minutes of standing, it's cooled down and the light is out at idle.

So... what to do? I'm tending towards dropping the sump at next service which is basically now and swapping all the big end shells. Is this worth doing? Is it worth trying to swap the mains too (and is that possible with the crank in situ - one of the end ones looks impossible to access unless the box is off..)

Or could it just be a old tired pressure switch? Checked the wire for chafing it's not that....

Assuming I drop the sump off, what else is there to look at? Pressure relief switch on the oil pump a good idea to service? There is a temperature sensor on the oil gallery as well I presume to send oil through that cooler on the right side of the rad? Don't know much about that.... comments would be welcomes....
Click to expand...

I would have thought, after that climb with a canny bit of weight, the engine and oil would be as hot as they are going to get. Unless you go pulling a 2tonne trailer through soft desert sand at 40 degrees C. I'm surprised the fan wasn't kicking in and would presume it was if the temp needle didn't go up. It's quite a height too, but because of liquids being difficult to compress I would think the change is pressure would have very little affect on the viscosity of the oil. If after 5 mins of just standing it's back to normal (no flickering light) then it would indicate a temperature issue. There might have been parts reaching temps that they have never reached before. Or, soaked at those temps for a length of time they've never been exposed to before.
I would go the gauge route too first. If the engine is running well, then you are going to a lot of trouble to replace the bearings when you may not need to. In reference to your question, the big end shells will be relatively easy to change in the car. The crank journals would be a nightmare and almost impossible (someone might come on and say they have done it) because the gearbox end of the crank is bolted to the flywheel and is then connected to the gear box input shaft via the clutch. The seal on the front journal is a nightmare to replace on it's own, even with the engine upside down on an engine stand in the middle of the garage floor and your looking down on it. I wouldn't even contemplate it lying on my back or even looking up from a pit. You'd need arms like Popeye. IMHO
If you decide to drop the sump, check the gauze filter/screen on the oil pick up to see if it is clogged with cr@p. Mine was fine at 180K, but then I reckon it'll dpend on how it has been serviced and anything can happen over that period of time. You can change the oil pressure relief valve from there, but then you were have low pressure problems.
 
Why do you say it the thread title "low oil pressure when hot " when obviously you haven't done an oil pressure test.
It seems you just relying on a £5.00 oil pressure switch to tell you, when u say that it the original oil pressure sender with a 160,000 on the clock.
The first thing is replace the switch, which quote old tired as they are known to fail

Why do we need all the waffle "20% mountain pass" etc etc? :rolleyes:
 
Al2O3 said:
I would have thought, after that climb with a canny bit of weight, the engine and oil would be as hot as they are going to get. Unless you go pulling a 2tonne trailer through soft desert sand at 40 degrees C. I'm surprised the fan wasn't kicking in and would presume it was if the temp needle didn't go up. It's quite a height too, but because of liquids being difficult to compress I would think the change is pressure would have very little affect on the viscosity of the oil. If after 5 mins of just standing it's back to normal (no flickering light) then it would indicate a temperature issue. There might have been parts reaching temps that they have never reached before. Or, soaked at those temps for a length of time they've never been exposed to before. .
Click to expand...

This is my suspicion - as I've not had issues with oil pressure before (sorry I mean I've not had issues with the binary indication from my old £5 sensor) I'm was tending towards the oil getting too hot and thinning too much rather than a bearing wear issue per se. But if I need to get the sump off to check relief valves etc (and possibly to tap in a sensor boss on the sump wall) I was thinking perhaps the bearings may be checked and replaced anyway for what they cost...

Any ideas on the temperature sensor - I'm told there is one that diverts the oil into the radiator cooler when it gets hot enough but I've not figured out where it is. I presume it's installed in the bracket for the filter but a quick look didn't show me much. I'll be getting a pressure gauge soon so I can check what the normal oil pressures are at hot idle and can assess from there...
 
I'm borrowing a mates set that he uses for autobox diagnosis - it has NPT connections but theres an adaptor to 10x1.0mm which is right I think and the gauges read 0-100 and 0-1500psi so that should be good I hope. If the pressure is over 100psi then the oil pump is doing epically well...... I presume RAVE or whatever will give be the correct values but I was assuming I should be seeing about 1-1.5bar at idle and 3 or more at cruising revs.
 
chris-the-gerbil said:
but theres an adaptor to 10x1.0mm which is right I think and the gauges read 0-100
Click to expand...

That sounds good,

Rave does have details of the pressure. Iirc the oil pressure relief cuts in at 55 PSI.

chris-the-gerbil said:
Any ideas on the temperature sensor - I'm told there is one that diverts the oil into the radiator cooler
Click to expand...

Iirc, Again, I came across it in rave when looking for details on mine a while ago. There is an oil thermostat , next to the oil pressure switch on the filter housing. Pipe then goes to the oil cooler.

Cheers
 
Changing the big end bearings without changing the mains is a waste of time. Worn mains are the main cause of oil pressure loss leading to big end failure. Unless you live in a cold climate use Land rovers recommendation of 15W 40.
 
Chief suspect IMHO is likely to be the oil pressure relief valve spring getting tired at that mileage .... or the oil pump...

I fitted an oil temp gauge to my auto cooler lines - just a cheapi off the bay - but after checking it with my IR thermometer, its not too far out - certainly close enough for the job at hand...

wammers said:
Unless you live in a cold climate use Land rovers recommendation of 15W 40.
Click to expand...

Agreed - the extra 5 points probably won't make that much of a difference - but make sure you're using the right oil for your ambient temps.

We run 10W 40 fully synthetic because our temps can drop to below -10 in the winter ( -17 is the lowest we've recorded, but this was inside the parlour, so it must have been bl**dy cold outside!!

OP:- If you've an "HGV direct" near you, they do a long drain 10W 40 synthetic for decent money. ( also 15W 40 )

wammers said:
Changing the big end bearings without changing the mains is a waste of time
Click to expand...

Agreed. Short term possible "fix" for a problem that needs more work. Thus, sadly, waste of time, and not even half the job, as I woudn't fancy polishing a crank in situ :eek:
 
At hot temperatures though both oils should be the same viscosity - the lower number is only for better flow when cold.

Should have an oil gauge to get some numbers tomorrow if my mate comes through so lets see what the numbers are first....
 
OK So I have numbers now...

Cold start, I get 3 bar (45psi) which if revved a bit to 1500rpm goes to about 3.75bar (55psi) and then doesn't climb. So I guess the pressure relief valve is working OK

After a short drive and the water temperature needle is just lifting off the bottom, I get about 1.5bar(22psi) at idle.

After it's up to temperature and I've done a few miles, I have 1.1bar (16psi) at idle, 2bar at 1500rpm and 3bar at 2200rpm etc.

Does that 1.1bar on hot tickover look a bit low? I've no idea what they should be I've not found any references to correct pressures for the engine in the overhaul manual.

Thanks.
 
upload_2017-6-15_14-26-28.png


From Rave.

Also, there are these videos

or this one.


Cheers
 
chris-the-gerbil said:
OK So I have numbers now...

Cold start, I get 3 bar (45psi) which if revved a bit to 1500rpm goes to about 3.75bar (55psi) and then doesn't climb. So I guess the pressure relief valve is working OK

After a short drive and the water temperature needle is just lifting off the bottom, I get about 1.5bar(22psi) at idle.

After it's up to temperature and I've done a few miles, I have 1.1bar (16psi) at idle, 2bar at 1500rpm and 3bar at 2200rpm etc.

Does that 1.1bar on hot tickover look a bit low? I've no idea what they should be I've not found any references to correct pressures for the engine in the overhaul manual.

Thanks.
Click to expand...
what type of oil and what weight of oil?
 
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