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MG MGB Technical - no oil pressure at gauge after oil change

Replaced oil cooler which had a leak and whilst doing so flushed oil and replaced oil filter. Refilled and started!! Yes I now know I should have spun without plugs, but in many years of changing oil in other cars I never had. No oil pressure showing. Removed rear oil hose and tried to fill with oil. No improvement. Off with oil filter. full of oil. With very large syringe pumped oil into hose till back pressure. Rocker cover off plugs out spun over.Oil at rockers. Ever so slight show of pressure. Started engine!! No oil pressure, but no untoward mechanical noise.
Advice so far is wrong oil filter, but checked and fine, but will replace with fram ph.2857a.
Jammed pressure release valve, but why would it jam open if no pressure?
Blocked gauge flex hose. This is next step and hope I haven't hurt the mains!
Help?
g goldthorpe

The first thing to check is if your oil pressure gauge is reading accurately. Substitute a mechanical gauge, at the engine, and observe your readings. If it shows as good, the problem is obviously in the gauge or line. If no pressure is indicated, you have a problem with the oil pump, oil pump drive spindle or improbably your oil pressure relief valve. RAY
rjm RAY

The oil curcuit is probably still not full after replacing the cooler. I've had this a couple of times when changing MGB engines or parts of the oil system. The fact that the filter is now full & oil is getting to the top of the engine means the pump is working. How long did you run it for? I'd be doing more cranking or even start it up & let it idle. If you dont see any pressure within about 30 seconds then switch off & investigate further but I reckon you will.
G Britnell

I drained the engine oil and took the oil cooler lines and gauge line off the engine when I was refurbing the engine bay. When I put everything back again the oil pressure took a while to come up. It still does. I don't get a reading for 5 to 10 seconds after the engine starts. I've been meaning to ask on here as to whether this is normal (only drove it for 20 miles before I dismantled everything).
Steve Church

Graham, Try a new oil filter, I fitted new oil pipes changed oil & filter to my '73 bgt, had the same problem as you.
The new filter I fitted was a Fram replaced it with a Champion 101 Full oil pressure in 2-3 seconds, would never use a fram filter again. regards Bill
wm griffiths

It takes a while to get oil pressure. Maybe 3 seconds,hard to say as it seems like an hour when you are watching the gauge. I changed the oil cooler and pipes on my car and it just ran for a bit longer than usual and then ping normal cold start 60 psi. I would suspect the filter.
Stan Best

Yes some filters are better than others at persuading the oil to stay inside them & not drain away when the car is switched off. I used to find the puralator ones very good & bought a job lot of them when I drove a BGT as my daily car. The current one on my roadster holds its oil well & I get instant pressure even after its been left a few weeks. Its a unipart one now. This replaced a halfords one that wouldnt hold its oil for more than a day & then I had to wait the 3 seconds or so to see pressure on the gauge.

I think the O/P's problem is that his cooler & pipes are still not full of oil though.
G Britnell

If you have the inverted filter and the anti-drainback tube sticking up from the filter head you need to make sure that there is enough depth up the middle of the filter to give at least 1/2" clearance, otherwise that can prevent any oil flow and pressure on the gauge. My tube is 2" long, the internal space on a Champion C102 I measured is 2.785", a Volvo 3517857-3 2.57", a Mann 916/1 2.75" and a Unipart GFE422 3.07". Out of these the Volvo gives the fastest pressure rise time although the Champion was only slightly longer, but the Volvo is a shorter filter so perhaps not ideal. More importantly they keep their rise time over their life (3k). A Fram advertised as having an improved anti-drainback valve was worse than these, and more importantly got slower over its life. The Volvo is said to be the same as a Mann 917/1, the 916/1 is longer externally (same as the Champion) but I haven't tried it yet, nor the Unipart. The Unipart is about £3, the Champion £5, the Volvo £7. Mann 917/1 don't seem to be available in an online search but a pal found some at Central Auto Supplies for £3, and I found a couple at Stoneleigh and on eBay for the same price.
PaulH Solihull

The taller the filter, the longer it will take to get up oil pressure. If the standpipe is 2 1/2", anything taller than 3" will allow the oil, which is above the standpipe, to drain back into the oilpan through the standpipe and then the oil cooler. One of the times where bigger is not necessarily better. RAY
rjm RAY

Bleed the oil capilary tube. Slacken the nut at the back of the gauge, with the engine running. Best with the gauge pulled. Catch the oil in something, doesn't take much to bleed any air.
Allan Reeling

Why will bleeding the oil gauge line get oil pressure back? 60psi is 60psi regardless of whether it is oil or air. I've bled and evacuated my V8 oil gauge pipe to see if it had any effect on the long pressure rise times of that cars and it didn't (neither did a larger bore tube), and that is a much longer tube than on the 4-cylinder. In any case air should flow through the capillary faster than cold oil, and due to the mechanical construction of the gauge (Bourdon tube that has to fill with oil and expand) even a bled tube has to move oil through the capillary to move the gauge.
PaulH Solihull

Based purely on having central heating systems rendered useless by a tiny pocket of air! And also air compresses and oil doesn't, I have always bled mine when the gauge has been out, just seems logical. How many times have you been told "that can't possibly happen"?? In fact I've been guilty of saying that, then had to suffer a very red face, so don't exclude anything, especially something which only
takes a couple of minutes. "Capillary".............a small space where liguid is attracted to go, as in capillary attraction! Hence it's always been my assumption that once filled with oil it stays there and won't drain back.
Paul, am intrigued by the long pressure rise in your V8. My V8 is much quicker than the 1800. Again an assumption;; that this is down to the filter being the right way up! Is your take off at the filter or the pump? Have you tried a gauge actually close to or on the take off to see if the delay is in the gauge plumbing, or the system itself?
Allan Reeling

You can test the gauge and tube leading to it by connecting a compressed air line to the engine end of the tube. As Paul mentioned above it should read the regulated compessed air pressure accurately.
60 psi air = 60psi on the gauge. Zero reading would mean either a blocked tube, blocked orifice where the tube fitting connects to the gauge, or defective gauge. I have done this exercise on my MGA and it definitely works. In that case it was a blocked orifice.

Ralph
Ralph

I had a clear nylon tube from the engine to the pressure gauge I fitted due to the metal pipe splitting. This type of tube is common on after market gauge kits. You can clearly see the where the oil is and where the rest of the tube is filled with air. Gauge worked perfectly. Bleeding is not the fault here.

Perhaps Graham could tell us what he has done since his original post.

Tony
Tony Oliver

Just curious, but how could you bleed the Bourdon tube to get oil into it?
You could certainly bleed the capillary piping but I would have thought that there would always be some air remaining in the Bourdon tube.

And as Paul said, pressure is pressure. (The heating oil example refers to flow and is a different issue.)

David
David Overington

The jeans I am wearing at the moment have a stain on the left shin. While replacing the speedo last year, I must have knocked the oil gauge connection, causing it to leak slightly. The oil dripped to the base of the dash panel. Whin this little reservoir was full, it overflowed and dripped onto my leg.

However, as already said, there is no need to bleed the tube, 60psi is 60 psi, gas or liquid.
Geoff E

As far as I was aware it was common knowledge that the V8 had a very slow rise time, and the gauge take-off was moved from the filter outlet to the pump to help 'overcome' this in Dec 73 (Clausager p148. Note that the pressure at the filter outlet still rises just as slowly, but the owner can't see it! Also unless there is a significant flow restriction in the cooler, filter or hoses I can't see it making much difference anyway. The larger bore tube I used was clear plastic to different gauge and reacted in exactly the same way when cold i.e. very slow progress along the tube in line with the slow needle rise.

A pal left his coil immobiliser switched off to crank until the gauge just started to move before he would allow it to start as he was worried about the bearings. However after having switched mine off when fully hot and left it to drip for a couple of days before removing the sump to check the shells, I found them all slathered in oil i.e. it just isn't an issue.
PaulH Solihull

My gauge take off is on the pump body. I've just been out and started the beast, after 2 weeks on neglect I have to say, it was up to idle pressure in 3 seconds! Logically one would expect that with a pump take off, assuming the pump is in good nick. When you say "slow rise time", what is it?
What oil are you using?
The shells might be slathered with oil, but then there is capilary attraction holding it there!!!
Allan Reeling

Only starts rising after 2 or 3 secs, takes several secs more to get to 42psi which is the cold pressure. Hot starts rising straight away, but still rises as slowly, but being hot may only rise as far as 15 or 20psi. 15W/50 (when I could get it), 20W/50, 15W/40, new oil or old are pretty much all the same although hot pressures seem a little higher with 20W/50 and 15W/50. Bearings all at or just inside the clearances for *new* bearings after 100k, and 200k on the unground crank. I don't mind what is keeping the oil there, the point is that *is* there :o)
PaulH Solihull

Doesn't seem that bad to me, cold idle is the same as mine, getting there a touch slower, but only a touch. Hot idle, 15 or 20, that's good. I'm using Morris' 20w50.
Allan Reeling

You have to keep in mind that U.S. engines were not designed for high oil pressure, but for high oil volume. It's still very common to see new U.S. engines registering relatively low oil pressure, while they still provide the engine with adequate lubrication. The Buick 215 was no exception to the rule. When I purchased a MB 300D, I couldn't believe how fast the oil pressure rose on startup and it always buried the gauge, except at idle. RAY
rjm RAY

Managed to get a couple of 5L cans of Unipart 20W/50 this week. I've been looking for Unipart Green off and on for a while, then suddenly thought about my local Unipart place just a couple of miles away (Der!). Not 'Green', but still 20W/50, it'll be interesting to see how that goes.

My roadster takes about the same time to start rising after a week or two standing, but then shoots up to 60psi pretty-well instantly. Overnight cold starts are immediate rise to 60psi, hot starts immediate to 25-40psi depending on how hot.

I was under the impression that the high volume/low pressure of the V8 was a factor of eight journals, sixteen hydraulic tappets and rockers and goodness know what else. I.e. no option rather than by design!
PaulH Solihull

Nope, that's American engineering for you. RAY
rjm RAY

Thanks for all the help guys. After replacing the oil pressure relief valve, not easy, it was the oil filter all along. Put new fram in and all well except now got 80psi think new spring was tougher and a touch longer. Rang suppliers and they still insisted filter was correct.
g goldthorpe

Hi again
Full story of fix in case any out there have same trouble, which I'm surprised doesn't happen more often if major suppliers use same filter codes. I now wonder if the inverted filter holder is longer than the original and causing the mistakes!
Took rubber pipe to rear of engine off cooler and used massive syringe to pump oil to pump. No change.
Replaced pressure relief valve. No change.
Took capillary pipe off. No oil rising.
Replaced new mann with new fram 2857a. 80-100 psi settled down to 80. Will probably put old pressure relief spring in as I have been told there are 2 types, one which used spacers in the valve. The new spring was about 4mm longer and tighter. MG owners didn't list 2 types but tech' was aware. Was 5 mins from taking engine out when decided to change filter after being assured by manufacturer and supplier that filter was correct!
I didn't bleed air from capillary tube and believe unnecessary. I also don't think priming the pump, as I did made any difference but may if following a rebuild. Any thoughts on 80 psi pressure? Shall I leave it with tighter spring?
Graham
g goldthorpe

Graham,

I'd be interested in knowing the Mann filter number and understanding the structure of your filter mount adaptor eg length of standpipe or not having that feature.

Accepting you are correct in the problem having been the filter, apart from a 'one-off' bad item, there must be a physical problem in the fitting of that particular Mann to your mount. Mann have a good reputation AFAIK.

On the oil pressure, not knowing what you were getting prior to changing the relief valve spring/filter, or the car year, my dealer manual for engines here up to 18GG (to late 71 I think) gives oil pressure as 50 to 80lb running (though I'd think the latter likely only on new/rebuilt units). The specification for the pressure relief valve is operating at 70lb (how come 80lb possible?) with a spring free length of 3" (76.2mm).

My 18GG does have the 'spacer' inside the valve cup. I typically run at 63-65lb pressure on an unbuilt bottom end at 130,000 miles with Shell Helix 20W-50 mineral oil. Hot idle is around 50lb.

Regards
Roger
Roger T

I have in the past posted my experience with an out of town customer MGB. He took the car to have oil and filter changed, asked for 20W50. Fortunately, I had beat it into his head to check the OP gauge, because when he drove off, he had about 5 lb pressure. Went back and they said "Oops, we put 5W20 in it." They changed it and told him it was OK now, So he drives off without checking the pressure until he is a couple of miles away, in city traffic - 5psi pressure! Had it trucked 100 miles to me. I opened the hood and said, "well, it is a very small Spridget filter." The internals of the filter were bent from contact with the standpipe. It was only the distortion from the bending that allowed any oil at all to get through; one hard acceleration would have scattered it. Some investigation revealed that there are MANY listings from several manufacturers that show the same small filter for "All MG with spin on filter". The filter referenced is about half the length of the ones I usually use for Spridgets, and of course also half the diameter and length of an MGB one. Evidently these people all copy the mistakes off each other's internet/computer listings.

FRM
FR Millmore

Roger t
Mann filter was w916/1
Ididn't measure the length of the standpipe on the inverted housing but PAULH says the mann has a length of 2.75" internal and when I examined the inside of the filter I could see where the standpipe had fouled.
Check out mg owners club spares and accessories for details of inverted housing. With shorter weaker spring was running at 60psi.
Graham
g goldthorpe

Graham,

I have been running Mann filters for some time with no problem, but they are W 917. The overall height is 3.25 inches (measuring the outside dimension).

I have found that the Frams that I have used don't have an effective anti-drain back valve.

Charley
C R Huff

80lbs. pressure is within factory specs. When I rebuilt my engine in the early '90s, I used the uprated spring. The gauge read 80lbs. then and and it still reads 80lbs. today. Glad to hear that it was something minor. RAY
rjm RAY

Something wrong somewhere if the Mann 916 fouled the end of the anti-drainback tube. As well as Fram having poor anti-drainback valves some of them don't have a bypass valve and the pressure on a cold start can burst the element http://www.youtube.com/watch?v=3vDz3dVLaaM
PaulH Solihull

This thread was discussed between 26/05/2011 and 10/06/2011

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