Oil pressure relief valve

[Edwin]

Hi All,

 

About three weeks ago I took part in a classic car rally with my TR6 which was very nice to do.

But I noticed that after about 40 miles the oil pressure became a bit low:

 

• 65 psi when started cold
  
• 30 psi at 2000 rpm fully warm
  
• 15 psi at idle and fully warm
  

 

 

So after reading a lot of posts on the forum I checked out the PRV and found out that the spring was only 38 mm. The TR6 bible states that the spring should be 40 mm. So I bought a new spring and plunger only to find out that the new spring is only marginally longer (38,5 mm) than the old one.

 

So my questions for you all:

 

• Are the oil pressures above something of a worry?
  
• Is the new spring OK or should it really be 40mm in length?
  
• I'm planning to test the new spring and plunger this weekend but could this really make a difference to the pressure?
  
• I know that the car is burning oil (coming in from the pistons) but could this cause low oil pressure?
  

 

 

Regards,

Edwin

[88V8]

The pressure relief valve governs the blow-off pressure, to protect the pump from overpressure when the oil is cold. Unless the ball or seat is worn or dirty, or the spring has collapsed, it will not influence the running pressure.

 

The pressures you mention are rather low. Presume you are using 20/50 oil?

The normal running range is 45-65psi at 2,000rpm.

However, it is possible to drive with low pressure for many years if you treat the engine as if it were made of eggshells - don't rev it, don't use large throttle openings. Not much fun though.

 

As routine maintenance, the bearing shells should be replaced after 50,000 miles. If yours have not been done then a set of shells may improve things. The oil pump may also be worn, but be careful if buying a new pump as I have heard that some repros are not very good.

If the oil pressure can be improved, it may then be worth trying a new set of piston rings to reduce the oil burning.

 

Ivor

[Guest ntc]

Hi All,

 

About three weeks ago I took part in a classic car rally with my TR6 which was very nice to do.

But I noticed that after about 40 miles the oil pressure became a bit low:

 

• 65 psi when started cold

• 30 psi at 2000 rpm fully warm

• 15 psi at idle and fully warm

 

 

So after reading a lot of posts on the forum I checked out the PRV and found out that the spring was only 38 mm. The TR6 bible states that the spring should be 40 mm. So I bought a new spring and plunger only to find out that the new spring is only marginally longer (38,5 mm) than the old one.

 

So my questions for you all:

 

• Are the oil pressures above something of a worry?

• Is the new spring OK or should it really be 40mm in length?

• I'm planning to test the new spring and plunger this weekend but could this really make a difference to the pressure?

• I know that the car is burning oil (coming in from the pistons) but could this cause low oil pressure?

 

 

Regards,

Edwin

 

 

Hi Edwin

Perfect when cold and hot at idle but not so at 2000 rpm

[Edwin]

I am indeed using 20W50 oil. I was planning to check the piston rings next winter and replacing the main bearing shells seems like the logical thing to do at the same time.

 

But yesterday I tried something that got me thinking about the PRV again. According to the specs the spring should be 40mm but mine is only 38mm. So I put a small washer between the spring and plunger so that the total length of spring and washer was exactly 40mm (with the old spring and plunger) and took the car for a drive. And to my surprise the pressure instantly improved to almost 80 psi cold and around 50 psi when warm at 2000 rpm.....

 

I still have to put in the new spring and plunger to see what that does to pressure.

 

But I'm a bit confused as what to do.. is this an acceptable situation (spring with washer)?

And does anybody have any comments about the fact that the spring should be 40mm according to the specs?

 

Cheers,

Edwin

Edited June 16, 2010 by Edwin

[poolboy]

I've had to do both add a washer to the spring to increase OP a few pounds and add a washer between the housing and the block to decrease OP, on different engines I should add.

Who knows how accutately these springs were actually cut and how being compressed for nearly 40 years affects them.

Somewhat related, the noses of the crankshafts vary in length, as well, as the result of being sawed off to length in the process of manufacture.

Edited June 16, 2010 by poolboy

[smizgals]

Edwin,

 

Moss do uprated ones and advise to be used with oil coolers. They are longer than the original ones and increased the oil pressure, which was OK, on my 5.

However, recently my gauge is reading rather high irrespective of engine speed so will have to see if that is the uprated spring or more likely the gauge gone faulty.

 

Stan

[Casar66]

Has anyone an idea at which rate/pressure the prv opens?

I want to use an oilfilter with a bypass valve which opens at around 36 psi.

Many thanks

Carsten

[Mike C]

Might be a bit low. I set the spring in mine to hold a maximum of 90 PSI oil pressure @ 4000rpm with the engine cold, using Penrite HPR30 full zinc oil. The the engine loaded and hot my oil system operates at about 60-65psi. 

Note I had to shorten the spring on a replacement Triumph Stanpart PRV as it was too long- I was getting well over 100 psi on cold starts

[ed_h]

3 hours ago, Casar66 said:

Has anyone an idea at which rate/pressure the prv opens?

I want to use an oilfilter with a bypass valve which opens at around 36 psi.

Many thanks

Carsten

The bypass valve in an oil filter works on the pressure across the filter, which will be very low on a new filter.  As the filter gets dirty, the pressure across it goes up.  If the filter gets clogged enough, the pressure will open the bypass and oil will bypass the filter.  The bypass doesn't respond to system oil pressure.

Ed

[Mike C]

Sorry. I was thinking about the wrong PRV. If the bypass in the filter doesn't open until the delta P across the filter gets to 36 psi then I'd say this figure is a bit high. I don't believe that manufacturer's would allow a filter to get that clogged before opening the internal PRV.

That would cut my operating pressure back to something like 30 psi- but I guess you would know you had a blocked filter well before that low pressure was reached and change it.

Do we get much choice on the oil filter PRV setting? 

 

[Waldi]

36 psi differential pressure on an automotive filter seems high to me, because the cartridge (not the cannister, this gets full oil pressure) needs to be able to resist this. As Ed indicates above, it is not a pressure loss for normal clean oil.

maybe it is to protect the filter during cold starts with thick oil? Which filter are you referring to?

Waldi

[Casar66]

I have really no clue about the operation mode wether of the PRV nor of the internal oil filter valves. For my TR6 I have always used the MANN 712. But then I got the advice to go for the MANN 719/5, because that filter has an anti drain back valve. That anti drain back valve secures good oil pressure directly from the start.

So I asked MANN, if I can use that kind of filters.

Their answer:
"We assume that the engine has a bypass valve on the engine side, then the valve with the lower opening pressure will respond first. "

 

And now??

[Waldi]

I think that supplier statement is correct but only in case the differential pressure across the filter element is higher than the 2.5 bar they specify. It must have good rigid internals. The advantage is you will always have flow with extreme cold (thick) oil.

Waldi

[Casar66]

So I can use that one?

[Waldi]

Carsten,

I would think so, if your supplier has recommended it. The catalog does not specifically refer to Triumph and only to Audi older models like 100, fwiw.

Like many catalogs, it does not show filter area, filter fineness and efficiency, but most buyers are not interested in that. I know a little more than the average about hydraulic systems and filtering, but that is an entirely different market.

Waldi

 

edit: I use a K&N HP2009, which has both an anti drain back and a by-pass valve. I think that by-pass opens at a lower pressure. Readily avaiable from Moss and others.

Edited March 22, 2020 by Waldi

[Mike C]

I reckon that this is is wrong:
"We assume that the engine has a bypass valve on the engine side, then the valve with the lower opening pressure will respond first. "  The oil filter's internal filter can only relieve pressure across the filter media  to somewhere within the filter case - unlike the engine's PRV which can relieve from the pump supply back to the sump. The two different PRV's are responding to different pressures.

 

[Spit_2.5PI]

+1 for MikeC's comment.

Cheers, Richard

[RobH]

+1 for K&N HP2009

[Waldi]

Mike,

I think it depends how you read this. Sorry, cannot say it clearer. I also understand what you say and that was my 1st thought too.

If our cars would have a prv setting at say 2 bars (and there are many low pressure systems), that internal filter by-pass will never open.

So the statement is correct, but for our cars less relevant.

Cheers,

Waldi

[astontr6]

On 6/15/2010 at 4:06 PM, 88V8 said:

The pressure relief valve governs the blow-off pressure, to protect the pump from overpressure when the oil is cold. Unless the ball or seat is worn or dirty, or the spring has collapsed, it will not influence the running pressure.

 

The pressures you mention are rather low. Presume you are using 20/50 oil?

The normal running range is 45-65psi at 2,000rpm.

However, it is possible to drive with low pressure for many years if you treat the engine as if it were made of eggshells - don't rev it, don't use large throttle openings. Not much fun though.

 

As routine maintenance, the bearing shells should be replaced after 50,000 miles. If yours have not been done then a set of shells may improve things. The oil pump may also be worn, but be careful if buying a new pump as I have heard that some repros are not very good.

If the oil pressure can be improved, it may then be worth trying a new set of piston rings to reduce the oil burning.

 

Ivor

I have to agree with Ivor, also the cam shaft bearings play a big part in the oil pressure figure. My car even with 96k on the clock still had very high oil pressure and the cam shaft bearing diameters were still well within tolerance but the cyl. bores were badly glazed so I did go for a rebore. In the end it depends how good do you want your engine to be? I did lap in the oil pressure relief valve! Be very careful on oil pumps as some of the County pumps have been  substandard.

Bruce.

 

[Mike C]

The original , bolt on , oil filters had no internal pressure relief provisions at all, and still worked - unless they got so clogged that all the oil diverted through the engine PRV- this has never happened to me but presumably the symptom of it happening would be the oil  pressure would rise to something like the cold start level.

[Casar66]

Quote

The original , bolt on , oil filters had no internal pressure relief provisions at all

Are you sure? Just yesterday someone with expertise told me different.

[Mike C]

2 hours ago, Casar66 said:

Are you sure? Just yesterday someone with expertise told me different.

You're right. I just checked in the BB and there's a relief bypass valve built into the original bolt on filters.

Edited March 23, 2020 by Mike C
Fact check

[DRD]

On 3/22/2020 at 9:30 AM, Waldi said:

Carsten,

I would think so, if your supplier has recommended it. The catalog does not specifically refer to Triumph and only to Audi older models like 100, fwiw.

Like many catalogs, it does not show filter area, filter fineness and efficiency, but most buyers are not interested in that. I know a little more than the average about hydraulic systems and filtering, but that is an entirely different market.

Waldi

 

edit: I use a K&N HP2009, which has both an anti drain back and a by-pass valve. I think that by-pass opens at a lower pressure. Readily avaiable from Moss and others.

What is the correct spec pressure for the bypass relief valve?

1bar or 2.5bar - the filters vary.

[AarhusTr6]

Hi

 

Interesting, is this something that should be checked every now and then?

Rich