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Braking Oil Pressure

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volts101

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'67 BJ8 with recently rebuilt engine and finned cast AL alloy oil pan by PO.
This could be a DW or Moss pan; they look similar from photos,
7.75 Qts (= 7.3 litres) of VR1 shows marginally above top dip stick mark.
My manual says 7.25 litres capacity including filter
Oil cooler fitted.
Normal running and idle OP is fine at hot 48/38 psi
cold 60/50

When oil is really hot - after a run after and after moderate hard braking say from 60 MPH (not panic stop) OP falls to zero for about 2-3 secs before recovering to normal - around 48 psi. Not noticed when oil is cold. Obviously hot oil slushing forward leaving pump sucking air. Oil pan does have the internal baffle.

I have a oil temp gauge and it does take a while for oil to get really hot ... about 45 mins to 170F

So what gives ?

Others have suggested that the oil pump pickup needs to be trimmed if DW high output pump?
Have no idea if this was done by PO or what sort of pump it is.
If this is the case then I don't understand why normal running OP is not affected ?

Maybe other cars do this unnoticed ?
Ideas welcome.
 
Hi volts,

My first thought was that the oil in the pan is evacuating the resident area of a loose pickup. But then, thinking further, I began to wondering if the pickup tube is secured on the pump properly and it may be moving to open an air intake much further up. This second thought would also be as a result of the movement of the pickup tube and, even if the screen were to be under the oil level, movement of the pickup tube would open an air intake into the pump and eliminate any vacuum draw.

The last and less likely thought passing through my mind is the loss of the timing chain pressure piston foot from its cylinder. Although this condition would result in a gauge-registered pressure loss, I don't believe its result would be as severe as to cause a total pressure loss and would definitly not recover to pre loss levels.

It is not totally uncommon to have a loss of pressure gauge pressure as a result of a hard stop. However, in most cases the pan's baffle holds a sufficient volume of oil in place to allow the pickup enough retained oil until the oil recovery. However, if the pan baffle is improperly positioned or the pump pickup improperly placed or loose, what you have described can be the result.

Just my thoughts,
Ray (64BJ8P1)
 
Sounds to me like your baffle is not up to the task. You don't ever want the oil pressure to drop to zero, not even for one second, you are potentially damaging bearing inserts whenever you have no oil pressure and if you do that very many times you will damage the crank journals too. I know, I raced for several years and destroyed lots of inserts before I finally cured the problem of oil surge with an Accusump.

The normal running oil pressure is still normal because you have been very lucky so far....

If you are driving aggressively enough to suffer oil surge leaving the pump pickup dry, there are cures like special racing pans. You can look at your baffle and see how it is intended to work - most of the aluminum sump baffles I've seen don't seem to be all that effective.

All oil pumps need to be trimmed when changing to an aluminum sump because the sump is much thicker so was probably done. But I don't think oil pump pick-up is the problem because, if it was the problem, it would be a problem all the time - not just when hot under hard braking.

DMD Australia makes a racing pan with several hingeds gates ala NASCAR but it still didn't cure the problem for me when racing (I see you are in Vancouver & you can probably relate - Mission raceways turn 1 was a problem for me) I have DMD racing pan I will sell if you are interested but, to be honest, the cure that worked for me is an Accusump.

If you are not familiar with Accusump, it is and oil accumulator (they make 1 and 3 quart versions and you want the 3 qt version) that basically stores oil under pressure and then releases that oil into your system under pressure whenever the pump fails to supply oil. End result is you never loose oil pressure. Depending on the valving you choose, they can also pre-oil your motor - when you turn the key on a solenoid valve releases the stored oil under pressure and you see pressure on the gage before you hit the starter - it's a very happy feeling seeing oil pressure before the engine is running.

I would drive milder until you can get a handle on it because you are running a risk of serious damage every time it happens.

Dave
 
red57 said:
Sounds to me like your baffle is not up to the task. You don't ever want the oil pressure to drop to zero, not even for one second, you are potentially damaging bearing inserts whenever you have no oil pressure and if you do that very many times you will damage the crank journals too. I know, I raced for several years and destroyed lots of inserts before I finally cured the problem of oil surge with an Accusump.

The normal running oil pressure is still normal because you have been very lucky so far....

If you are driving aggressively enough to suffer oil surge leaving the pump pickup dry, there are cures like special racing pans. You can look at your baffle and see how it is intended to work - most of the aluminum sump baffles I've seen don't seem to be all that effective.

All oil pumps need to be trimmed when changing to an aluminum sump because the sump is much thicker so was probably done. But I don't think oil pump pick-up is the problem because, if it was the problem, it would be a problem all the time - not just when hot under hard braking.

DMD Australia makes a racing pan with several hingeds gates ala NASCAR but it still didn't cure the problem for me when racing (I see you are in Vancouver & you can probably relate - Mission raceways turn 1 was a problem for me) I have DMD racing pan I will sell if you are interested but, to be honest, the cure that worked for me is an Accusump.

If you are not familiar with Accusump, it is and oil accumulator (they make 1 and 3 quart versions and you want the 3 qt version) that basically stores oil under pressure and then releases that oil into your system under pressure whenever the pump fails to supply oil. End result is you never loose oil pressure. Depending on the valving you choose, they can also pre-oil your motor - when you turn the key on a solenoid valve releases the stored oil under pressure and you see pressure on the gage before you hit the starter - it's a very happy feeling seeing oil pressure before the engine is running.

I would drive milder until you can get a handle on it because you are running a risk of serious damage every time it happens.

Dave
Click to expand...


Dave,
Thank you.
I think that your experience nailed it - that the baffle in my pan is just not up to the job.
Like your suggestion of the Accusump. Mounting will be the issue. Plumbing shouldn't be too difficult as already have oil cooler lines.
Yes agree pre-oiling is the bees knees !!
Roger Grace
 
Hi All,

Dave, I appreciate your experiences on this mater and, although I now consider myself as more of a cruising driver, in my younger years I was considered aggressive. I have always used the original sump on my engine and, although I never experienced a loss of pressure as a result of heavy stopping, I did experience momentary reduction in pressure.

Roger, how aggressively are you jamming the brakes to cause your loss of pressure? Have you compared the baffles in your aluminum pan with the placement and height of the original? I appreciate an short or instantaneously heavy application of brakes will cause some transfer of oil in the sump so how long are you applying the brakes to cause the massive transfer of sump oil?

Yes, a badly designed after market sump can be your cause but I am wondering if a badly positioned pickup could be more likely amplifying your condition. Either way, I would pull the pan and examine the baffle and position of the pickup.
 
Roger,

Ray raises a good point about the height of the pump pickup that I failed to focus on earlier - whoever installed the aluminum sump may have shortened the pickup way too much. It should be picking up within an 1/8" or so of the bottom of the pan but if it's and inch off the bottom of the pan, that would certainly aggravate the situation. And, the hotter the oil, the lower the viscosity, and the easier it can slosh away so that would fit with your experience.

I agree with Ray, next time you have the pan off, study the baffle to see how it's designed to work. Pour some liquid into the pan (doesn't have to be oil, can be water or parts washing solvent, or?) and try sloshing it around by hand - you may be surprised at what you see - some baffles actually seem to keep oil away from the pickup :(. I know it's a crude test but it can be revealing.

I tried an aluminum sump about 25 years ago and found the surge problem with that baffle was worse that it had been with the stock pan - that's what led me to the DMD racing pan. As I said before, it was definitely better but still didn't fully cure the problem for me.

​
Dave
 
Ray and Dave your experienced input appreciated.
Yes I do intend to pull the pan to see what is going on with the pump and play with the sloshing test.
Unfortunately I don't have a standard steel pan to compare it to. I suspect that this AL one may have different baffle size and location.
Also on further reflection, think it is also a braking time issue. This does not happen if I jam the brakes from a slow speed. Its the starting at higher speed and longer hard progressive brake for several seconds that makes it happen. Also when the oil is really hot. Not done the same test with cool oil as generally don't like RPMs below 150F oil temp.
Is there a simple way to recognize a DW high output pump ?
Having said all this do also like the idea of adding the Accusump but not easy to fit.
Dave - typically how long can the engine stand unstarted before the 3qt accumulator pressure drops ?
Tkx guys
Roger
 
I've done my share of hard stops, etc. and have never encountered such a condition. I'm going to suggest that before dropping the pan, etc. you make sure that pressurized lubricant is getting to the OP gauge--first by loosening the connection at the flex line to run any air out of the line and second, if the issue still repeats to do the same at the gauge head.
 
Roger,
This may help some. Picture of a stock tin pan, you can see there are only two baffles, both seem to be to reduce forward surge under braking - one large one in the sump area and one up in the higher forward part of the pan. Also, these are very large capacity pans.​
IMG_3391.jpgIMG_3390.jpg

And here is a pic of the DMD racing pan. It shows some of the hinged gates designed to let oil surge in but not surge out. As I said, it was an improvement in that oil starvation was much rarer, but it still happened in some scenarios. I never had problems with straight, hard braking but rather after hard braking from say 80 to 20 into a hairpin turn where you get right back on the throttle after turn-in - I would sometimes see the oil warning light for a second....and then the oil pressure would be a couple of pounds less. You can imagine the oil had surged forward from the braking but then surges to the side from turning and eventually you are dry at the pickup. For street driving, this pan might be sufficient and has a second advantage of being about 1" shorter than stock so it does not extend below the frame line allowing a skid plate if desired. However, I still think the accusump is the best way to go, short of going to a dry-sump.​
IMG_3395.jpg

I don't have an aluminum sump or baffle to show but most of the ones I've seen are a fairly small circular baffle that surrounds the stock oil pump pickup strainer with some hinged gates - I'm not a fluid dynamics engineer but they seem too small to me.

As to identifying the oil pump you have. Here is a picture of a Denis Welch gear type pump (what they call 'normal' as opposed to what they call 'high output'). As you can see they have there name and logo cast into the pump body and I imagine they do the same with the 'high output' pump. BTW, what they call high output is the early rotary vane pump used in the 100-6 and very early 3000 to April '59, engine 29D/895, and what they call normal is the gear type that came in all subsequent 3000s. Most all racers use the gear type because, if you are running at high revs, the rotary vane type can overload the oil pump drive gears on the cam - I have a friend with a Denis Welch race cam that is junk because the oil pump drive gear failed on track after about 2 hours.

IMG_3388 (2).jpg

If you are driving aggressively enough to have this issue, I suggest installing a warning light - put a tee in the fitting on the block where the oil pressure gage line attaches and insall a sending unit there because a bright red light will be noticed when you might not be looking at the gauge.

Having said all the above, it does seem surprising you are having this problem with just straight line braking.

Dave

Forgot to add, I didn't use mine as a pre-oiler, just had a ball valve and turned it on before going on the track and in this scenario would hold pressure several days easily. Since I didn't use a solenoid valve I never tested long term it but my guess is, if the valve on the accusump is good, it would hold pressure as well as a tire does :smile:

​
 
Thanks to all.
Have at last found a photo of my AL pan - with silicone gasket in place BEFORE cutting the oil return notch.
Comparing to the stock tin pan it only has one forward baffle and not the curved one.
Maybe this is my problem ?
Would be interesting to know the source - would have thought that they all would be the sme given the pattern costs.
Have another oil pressure gauge that will also try.
However after all comments to do too many tests.
Tkx
rg
 
Hi Roger,
Your pan baffles look very similar to the stock pan. The front thing in the stock pan is, I think, a stiffener rather than a baffle - wouldn't do much as a baffle since the oil pump pick-up is in the lower rear section.

Can't tell from your pictures but I'm guessing the main baffle in the lower compartment has gap between it and the floor of the pan similar to the stock one shown in one of my pictures above. As you can see in my pic of the stock one, there is a small gap along the floor, maybe 3/16" or so and the corners are open a bit to allow oil to flow in but be blocked from suddenly flowing out when braking. In other words, it looks to me like it would work as well as the stock pan.

I have seen additional baffles in aluminum pans, but don't know how effective they are. In your picture you can see there are 4 small flats in the corners of the main sump about the same height as the forward pan bottom. I have seen these drilled and tapped to bolt in a baffle consisting of a flat metal sheet welded to a round tubular 'can' shape (open top and bottom) going down to near the pan floor that would be just a bit bigger than the stock screened pump pick-up. In some cases I've seen these 'cans' end a little above the pan for oil to enter under the 'can' but I have seen some that nearly touch the pan floor and have four small hinged 'doors' that hinge freely inward for oil slosh to push open and fill the area inside the can and then close against the inside of the 'can' when the oil sloshed the other direction to keep the oil inside the 'can'. Again, I don't know how well any of these designs actually work because I went to the Accusump and quit worrying about baffles (in fact I'm now back to a stock pan).

Dave
 
IIRC, my DWR sump has a different baffle than the one they show now (but that was 20 yo that I looked at it).

I also see that DWM now has a low-profile sump.
 
red57 said:
Hi Roger,

Can't tell from your pictures but I'm guessing the main baffle in the lower compartment has gap between it and the floor of the pan similar to the stock one shown in one of my pictures above. As you can see in my pic of the stock one, there is a small gap along the floor, maybe 3/16" or so and the corners are open a bit to allow oil to flow in but be blocked from suddenly flowing out when braking. In other words, it looks to me like it would work as well as the stock pan.
Dave
Click to expand...

I think I see a significant difference between Rodger's Al pan and the stock one. As Dave mentions the large baffle appears to have the holes in the bottom but it does not have the openings in the corners. My thought is that on hard and maybe long braking the oil can run forward away from the pick-up but it can't get back to the deepest part of the sump very quickly because the bottom holes are too restrictive. During the period of a braking cycle the oil has time to go forward under that momentum but when letting up on the brakes the oil only slowly can get back to the pick-up. Just a thought.
 
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