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What is good oil pressure ? Addverts read ( has good oil pressure) can some figures be put down.

 

On start up oil pressure wil read what **** Mine is about 80

When warm approx 15 minutes driving and at 2750 revs approx 70 mph what ***** Mine is about 60

When warm approx 15 minutes driving and at tick over what **** Mine is about 35+

 

I have a slight oil leak back of engine, possible crank float ( got this from other forum posts ) Other than that engine seams pritty sound or is it does it have good oil pressure ????

 

1972 TR6 PI

 

 

Regards Alan

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Hi Alan,

 

This topic is always subjective to some degree - and I'm no exception <_< . Your pressures are probably fine as they are, but I think they're low for a new engine.

 

For my part, I want to see 70 psi @ 70 mph in top/OD ( = 2700 rpm ) when the oil is as hot as it gets; i.e. after 40 minutes of operation. My driver's engine has 75000 miles on the bottom end and gives that pressure still, but I do have an oil cooler now ( without this it would be ~ 65 psi ). It will show ~ 20 psi @ 600 rpm when fully hot. I use Kendall 20W50, which gives about 5-7 psi more than Castrol or Pennzoil " equivalents ". I do suspect that oil viscosities have dropped a bit in recent years, among the major brands at least.

 

My show car with 600 miles on it gives 10-15 psi more across the range, without cooler, and cold it stays pegged on 100 psi when moving for the 1st 10 minutes or so. Very satisfying indication of bearing fit for my new engine ;)

 

The TR250 Owner's Manual says oil pressure should be between 45 and 65 psi @ 2000 rpm when hot. I have always wanted mine to be at the top of that range...

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Thankyou gents

I have a standard engine with no oil cooler or electric fan and plan to keep it that way if possible, the next question would be what is bad oil pressure or when should we start to question the quality of our engines ?

 

Alan

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  • 2 months later...

Ok, so this seems to be a topic continually revisited! There doesn't seem to be answer as to what constitutes good oil pressure, but there surely must be for bad?

 

I only drive mine locally on a regular basis and oil pressure's fairly stable at around 50psi, but can drop to 25psi at idle - which I'm quite comfortable with. On the rare occasions I drive longer than an hour (or 45mins in the summer), it'll start to idle at very low levels - to the point that the oil pressure warning light comes on. That's when I start worrying and revving constantly at lights (which just makes me look like a boy racer!) to keep the pressure up; it does put me off longer road trips.

 

I've read some of the considerable debate about oil coolers and the concensus seems to be avoid them if you're in temperate climes. Certainly on a day-to-day basis, it sounds like it would be a bad idea, given my short daily trips. So what's the alternative?

 

FYI, My TR had a recent injector service and an engine rebuild around 3 years ago. Otherwise it's also a standard engine and runs perfectly with stable water temperature and normal idling (~950rpm) when warm - it's just the oil that seems to get a bit hot after longer stints...

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I only drive mine locally on a regular basis and oil pressure's fairly stable at around 50psi, but can drop to 25psi at idle - which I'm quite comfortable with. On the rare occasions I drive longer than an hour (or 45mins in the summer), it'll start to idle at very low levels - to the point that the oil pressure warning light comes on. I've read some of the considerable debate about oil coolers and the concensus seems to be avoid them if you're in temperate climes. Certainly on a day-to-day basis, it sounds like it would be a bad idea, given my short daily trips. So what's the alternative?

You could fit a cooler provided you combine it with a stat. Although as you say it's not really necessary.

 

As you've found, it takes a long time for the oil to get up to temperature. Everything has to be heat-soaked, an hour, or 30/40 road miles at a decent speed?

I believe you do mainly local driving. Very short runs are death to an engine. Disproportionate time on rich mixture with bore washing, many cold startups each of which is more damaging than an hour's running, and oil that never gets hot enough to drive off water vapour and other contaminants.

Oil pressure collapses when those contaminants reach such a level as to dilute and degrade the oil, and this shows up initially at idle. I believe this is likely the cause of your problem.

 

I don't know why your idle would drop excessively after an hour - to what revs does it drop ? - but in a sense that is another issue.

My engine has 25/28 psi at idle, which is maintained down to 600rpm or so.

 

If you cannot avoid regular short hops I think you need to be changing oil and filter every 2,000 miles, perhaps even after 1,000.

With a good 20/50 such as Duckhams (other oils are available :P ) this should at least minimise the damage, and maintain a decent oil pressure.

 

In the 70s my wife used our MGC to go to work, a large engine run 4 miles rather slowly, the oil rapidly became unfit for service.

Big engine short journeys = doom :( . Fortunately I wrote it off in a head-on smash before it ran a bearing.

 

Ivor

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Cheers Ivor - I think you're quite right (on all points!). I'm fairly religious about warming up the car before every short (fast!) run, but it never gets a chance to get actually hot.

 

So, the solution to poor oil pressure when hot is basically just very regular oil changes then? Makes sense! Just changed mine last week (and yes, there was some emulsification) and planning a longer run tomorrow, so will see how she fares.

 

Thanks! T.

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You could fit a cooler provided you combine it with a stat. Although as you say it's not really necessary.

 

As you've found, it takes a long time for the oil to get up to temperature. Everything has to be heat-soaked, an hour, or 30/40 road miles at a decent speed?

I believe you do mainly local driving. Very short runs are death to an engine. Disproportionate time on rich mixture with bore washing, many cold startups each of which is more damaging than an hour's running, and oil that never gets hot enough to drive off water vapour and other contaminants.

Oil pressure collapses when those contaminants reach such a level as to dilute and degrade the oil, and this shows up initially at idle. I believe this is likely the cause of your problem.

 

I don't know why your idle would drop excessively after an hour - to what revs does it drop ? - but in a sense that is another issue.

My engine has 25/28 psi at idle, which is maintained down to 600rpm or so.

 

If you cannot avoid regular short hops I think you need to be changing oil and filter every 2,000 miles, perhaps even after 1,000.

With a good 20/50 such as Duckhams (other oils are available :P ) this should at least minimise the damage, and maintain a decent oil pressure.

 

In the 70s my wife used our MGC to go to work, a large engine run 4 miles rather slowly, the oil rapidly became unfit for service.

Big engine short journeys = doom :( . Fortunately I wrote it off in a head-on smash before it ran a bearing.

 

Ivor

 

Ye gods, my oil pressure on my earlier TR6 CR was about 25 at idle when hot and about 60 at 3k revs. On my current CP 5 the pressure never drops below 45/50 and is about 75 at 3k revs. I have an oil cooler , no thermo, tend to do 20 mile runs as a min and normally more at reasonable speed ie 60+. I believe the spring for the pressure vvalve is upgraded but not sure, oil is Penrite. Cars been fine so havent been concerned till I read this thread

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And just how many of these oil pressure guages have been calibrated in the last 30+ years?

One car's 60psi may well be another's 80!

Don't read too much into the exact figures - if you've had the car for a while & the pressures are remaining steady over time then don't worry. It's normal for the pressure to be high when cold & drop as the oil warms.

If they've dropped abruptly from last week or last month then maybe there's a problem.

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True, but I am concerned it's dropping too low when very hot - the oil pressure warning light keeps coming on when idling. Justed tested after a long run yesterday and recent oil change (to rule out my regular short trips degrading the oil) and oil pressure does seem to drop dangerously low, but only after an hour or so. When just warm - i.e. after maybe 10 minutes, there's good oil pressure, with up to 50psi at idle.

 

My temporary workaround is to open up the bonnet and up the idle speed when it gets hot. Around 1,500 rpm seems to keep the pressure just high enough to stop the warning light coming on (around 15psi?). Longer term, though, what would my options be? 10w-60 oil? Manual/stat controlled oil cooler? New oil pump? Or bearings/thrust washer replacement? Thanks!

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If the oil pressure warning light shows at tick-over, it is indicating that the oil pressure has dropped below the setting on the pressure switch. It does NOT mean that oil has ceased to circulate. And the circulation of oil is what matters, as it both lubricates the bearings AND removes heat. In fact, in the life of your engine, the removal of heat by the oil is as important as removal of heat by the coolant circulating through the block and head.

If the warning light shows at tick-over, I would not blip the throttle - that's just creating more heat in the engine, and that's not something you need in a traffic jam!

When the engine starts to rattle badly on start-up, that's the time to start worrying and planning a re-build! That said, modified engines, which will have greater tappet clearances, will tend to rattle for the first couple of miles, and one just has to put up with it!

As has been said, the best treatment for the engine is to get it really warm whenever it is used - that way, the water vapour in the sump will be vapourised and expelled from the system by whatever route your engine uses (mine goes to atmosphere, later cars suck it into the combustion chambers). And the oil pressure gauges are mass-production items which were built and calibrated many years ago - mine has never been re-calibrated and I bet very few have.

Ian Cornish

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Hmmm, ok. So you're advice is not to worry about it? Ok, many thanks! Certainly she's running extremely smoothly at the moment - it's only the oil pressure drop that has been concerning me. But it's a rare enough occurence that I drive her that long and I will continue to try and stick to 6-monthly oil changes due to my daily short trips. Cheers!

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If the oil pressure warning light shows at tick-over, it is indicating that the oil pressure has dropped below the setting on the pressure switch. It does NOT mean that oil has ceased to circulate. And the circulation of oil is what matters, as it both lubricates the bearings AND removes heat. In fact, in the life of your engine, the removal of heat by the oil is as important as removal of heat by the coolant circulating through the block and head.

If the warning light shows at tick-over, I would not blip the throttle - that's just creating more heat in the engine, and that's not something you need in a traffic jam!

When the engine starts to rattle badly on start-up, that's the time to start worrying and planning a re-build! That said, modified engines, which will have greater tappet clearances, will tend to rattle for the first couple of miles, and one just has to put up with it!

As has been said, the best treatment for the engine is to get it really warm whenever it is used - that way, the water vapour in the sump will be vapourised and expelled from the system by whatever route your engine uses (mine goes to atmosphere, later cars suck it into the combustion chambers). And the oil pressure gauges are mass-production items which were built and calibrated many years ago - mine has never been re-calibrated and I bet very few have.

Ian Cornish

Your oil light should not come on when the engine is running. It was put there to let the driver know they have a problem, not to let the driver know to "blip" the throttle. Set the idle to about 850 to 950 rpm. If you cannot get the car to idle properly, fix PI system, or take to someone who can. If the gauge is reading low, and the light is on, then, you have bearing, oil pump, rocker shaft problems or, to put it mildly, you need an engine overhaul. Also, if you are running an external rocker oil feed line, throw it in the trash can, nothing but a sales tool that floods the top end with oil, and can cause lower oil pressure, and oil consumption.

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Referring to the TR250 Owner's Manual, the oil pressure should be " 45-65 psi @ 2000 rpm when hot ". Inside these parameters there should be no need for concern ;) . Below this value says there is a problem <_<

 

As for gauge accuracy, these seem to be quite good IME. You can get a ~ 5 psi variance when fastening the oil line as there is a little angular play in the dial. If it reads spot on zero at rest it's telling the truth.

 

I'd swap the PRV with a known good one to see if, happily, it makes a difference. If not, you can drop the sump and change the bearing shells in a few hours ( including mop-up operations ). Oil pumps last indefinitely but are cheap enough and can be replaced at the same time - but some have excess clearances as new :( If there is insufficient pressure after that, curing it will mean engine out :(

 

As for the rocker feed line, I've used one of these for ~ 80,000 miles on a rebuilt engine and its oil pressure is AOK ( 60+ psi @ 2000 when hottest ) and consumption on my recent voyage was 1 U.S. qt / 3700 miles. I chose not to use one on my show car as the refurbed rocker shaft assy is much more wear resistant than original.

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Hmmm, ok. So you're advice is not to worry about it? Ok, many thanks! Certainly she's running extremely smoothly at the moment - it's only the oil pressure drop that has been concerning me.

Sorry to be a moaning Minnie, but this engine was 'rebuilt' three years ago? Since when it has done little mileage?

Then you were quite right to be worried. The oil light should not come on at idle, you should have pretty much 25psi whether hot or stinking hot.

Your 6 month oil change is good - about 1,500 miles? And filter....

 

Your oil light should not come on when the engine is running. It was put there to let the driver know they have a problem.

Set the idle to about 850 to 950 rpm. If the gauge is reading low, and the light is on, then, you have bearing, oil pump, rocker shaft problems.

I agree. And that's a good point - check that the plug hasn't fallen out of the end of the rocker shaft, that will undermine the pressure.

 

Just to embark on a slight but related digression, I've only changed Rover V8 main bearing shells with the crank in-situ. Big ends, no problem, but the mains were tricky as you have to use a stub in the crankpin oil hole to rotate the shell out. Given the TR6 engine has done about 45,000 since blueprinting, I was contemplating a bearing swap next winter as a matter of routine maintenance. So any problem to do the mains as well as the ends?

 

Ivor

Edited by 88V8
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I was contemplating a bearing swap next winter as a matter of routine maintenance. So any problem to do the mains as well as the ends?

 

Ivor

 

No. I've done this twice and the shells came out willingly. Gearbox was in situ so I suppose this supports the crank at the rear while the timing chain supports the front. Scant noticeable drop anyway.

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Yes, we do need to be aware of the relief valve, although I have never found any problems with the ones I have checked. In regards to the rocker feed, you will run lower oil pressure, due to more oil going to the rockers, instead of the crank. Maybe 3 lbs. when hot, maybe a little less. If you have good oil pressure, there will always be plenty of oil going to the rockers. Also, if you use a reground camshaft instead of new, you will not have as good oil pressure at hot idle as you would with a new camshaft, due to the bearing surface wear on the used camshaft. In regards to oil pums, I came across a brand new OEM oil pump. I checked the clearances on the OEM pump, and a county brand that had about 3k miles on it. Both were within specs, however, the county had less clearance than the OEM, which would mean a little higher oil pressure. So, I sold the OEM on ebay, because the county is as good or better. In regards to bearing shells, I have had little success with replacing the rod and main shells, or no success as far as oil pressure goes. The last car I did, had 80k miles on it. After replacing the rod and main bearing shells, the oil pressure was the same after about 50 miles of driving, as it was before the change, 25 when hot at idle. If you mic the crankshaft very close, you will find the problem is the crankshaft journals tend to wear lopsided, you can see this with careful use of a set of micrometers, particularly the rod journals. This has been my experience. As far as oil pressure goes, normal is when hot, hot means drive it at least 25 miles on the M 1 at highway speeds, further if it is cold outside, should idle at 25 psig at 850. If I remember right, if you use an infra red thermometer, the oil pan will read about 200 def. F when hot. Also, if it is below 30 deg, F outside ambient, it is difficult to get the oil hot no matter how far you drive. If I needed a little oil pressure to get the light to stay out, I would blueprint the oil pump, and/or run heavier oil.

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Hi Telster,

during the rebuild 3 years ago was the oil pump looked at. If it is worn then you will lose pressure when hot at tick over.

 

Roger

 

Hi guys. Thanks for all that. But now I'm back to being worried! The rebuild was done by the previous owner, shortly before I bought my TR6, so I'm afraid I have no idea what was done and what wasn't! It's quite possible the oil pump wasn't touched for example and I know it wasn't a perfect job because he never touched PI unit when converting to unleaded! Something worth investigating I guess...

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Hi All

 

Just to add my tuppence worth. I recently added an oil cooler/stat/longer oil filter to the spin on and changed the prv to an "upgraded"one. Now I dont know which of these factors have incresed my oil pressure, but its higher than before (it wasnt bad before) but when I removed the prv there was an area that was obviously worn. I wouldnt be able to measure how much. I wonder how many "low" oil pressure situations could be cured by checking whether the prv is not seating properly.

 

Mark

 

ps The car appears to run smoother.

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Just a quick question. Being from the US and a 20 year TR owner, I'm unfamiliar with the term tick over. What is that? Thanks, Sean

 

Hi Sean,

 

Tick over is a another term for idling...ticking over. A bit like what the economy is doing at the moment all over the world.. :D

 

 

Cheers

 

Tony

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