Rising oil temps/falling oil press

·         Russel Green

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I'm new to your Forum, so Hello Doug. I see you are very hands-on with this Q&A --- Well Done! Sorry to take up more of your time but I have not gotten any answers elswhere.
I have a Jab 3300 ser# 615 (solid lifter) with 500 hours. AeroShell W100. Standard Jab oil cooler (no Vernatherm), fitted tight to the NACA inlet, with plenty of exit area. Over the last 1 1/2 years I have seen a steady drop in average oil pressure, and a steady rise in average oil temp. I have put a 2nd washer in the pressure relief valve, cruise pressure now back up to 42. But that made no difference in my rising temps. (I live in a very mild climate) I had the cooler tested for flow & pressure. It's bad enough now that I have grounded the airplane.
I have run across some info regarding the oil pump reassembly: doing it wrong can misalign w/cam. When I went to view/buy the plane, I had found out about the upgrade backing plate and rather than go there, decide I wanted the plane (with a 3 day Xcountry to home), then wait for a week while part was shipped & installed, I had an A&P --who was local there but unknown to me-- get & install the part before I went to see the plane. Very possible he did not read the manual regarding this misalignment. So Questions: Does 200 hours sound about right for this to become a problem, resulting in the 2 symptoms I've described? Or does it just work until full failure? Is it the camshaft nose end that cracks? Is there anything visual to see with the pump off? If misaligned, would that slowly ruin the camshaft bearing there? Would that be enough to make oil press go to 35 @ cruise and temp quickly climb to 245 F? Is that bearing replaceable from the outside?
I just talked to a mechanic about these 2 simultaneous symptoms and he said that's a pretty classic description of main crank/camshaft bearing wear. Very loose bearings losing oil pressure which would mean reduced flow thru cooler. Makes sense except for the part where my engine only has 500 hours. Have been diligent about oil/filter change at 25 hrs. And if the poor cooling is a result of poor pressure, why wouldn't I see cooler temps after I boosted pressure at the relief valve?
Thoughts??
Russel Green

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·         Doug Smith

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Hi Russel, good to hear from you.
Thats an interesting one, with a few potential suspects.
Firstly, i doubt misalignment of the pump per se is the issue- when that happened (and it's been years since i saw one go) the end breaks off the cam and you know all about it very quickly (bad noise, no oil pressure, engine stoppage).
Next, the solid lifter engines aren't often troubled by bottom end wear unless there's been an issue at some point. At 500 hours i would be surprised if you have an issue there big enough to cause what you've described.
There are top end issues that can lead to these symptoms - for example excess blow by the pistons can elevate case pressure and temp, thereby affecting oil temp and pressure - but you'll usually spot that by bad leak down results, excess oil use and lots of oil in the catch bottle.
Is your oil cooler the positech/aero classics unit or the long flat transmission cooler type? The former are preferred.
Assuming all is well in your top end, I think the first place I'd look would be the oil pump (again). They can wear, particularly if they're not installed with both the rotating parts in the correct orientation. The port plate and port plate can also wear or the seal to the case degrade and cause problems (any leakage on the negative pressure side of the pump is bad news - introducing air into the system. The other potential is the seal of the sump oil pickup tube to the case - and again you'll be able to check that, you an extent, when the oil pump and port plate are off. A bit of a hassle but less so than splitting the engine!
Hope that helps!
Doug.

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·         Russel Green

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Thanks Doug for a very prompt reply. I didn't include cyl comprssn #s because I didn't think they would be relevant to oil issues. Silly me. My cyls are all in the high 70's and are playing nicely regarding oil consumption. And yes, I'm aware of the correct dipstick level reading (halfway between marks) So we're pointing toward the pump.

I see in manual that some older pickup tubes were pinned to case, others press-fitted with a widening end. Will I be able to see which I have, and if loose, how do I tighten? Press-fit seems like an appropriate-sized socket and a little tap should do it, but pinned?

The overhaul manual I have is JEM0001-4 dated 17 April 2013; in chapter 9.5 Table 12 it gives the clearance values for Rotor End Clearance as "0.03 -- 0.006 mm". Is the .006 value a typo? Should it read 0.06?

Your response here reads like it's possible to have good pressure readings on the gauge but have actual low pressure to the cooler; is that correct? When I put a 2nd washer in relief valve and was reading 42psi at cruise, I really expected a drop in oil temp, but there was no change. That really stumped me.
I tried to attach photo of oil cooler but the website wouldn't accept the size of file. It's about 5" wide, 8" tall, 2 1/2 to 3" deep with a domed/rounded top. I believe that's the preferred Positech model you mention? The fins are all in good condition and straight.

Russel

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·         Doug Smith

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Hi Russel,

Those leak down numbers look fine, yes.

Unfortunately the oil pickup seal is not something you can really adjust per se... Once the pump and the port plate are removed you should be able to slide something clean down the inside of the tube, gently wriggle it and see if there's any movement. If there is you can try giving it a clean (something like Aerostart) and applying more sealing goo... you could try something like Loctite "Wick In" or Loctite 518. If there's a leak there and you can't seal it from the pump end then, unfortunately, it's case-splitting time to fit a new O-Ring and goo on that tube.

I can't look up the drawing for the oil pump right now but I'm sure 0.006 should be 0.060; 0.006mm is nothing.

Well, the pressure you read on the gauge is a little different from what the engine sees but that wasn't really the main idea... If you're getting air into the oil pump then it reduces the flow rate of oil through the system, which means there's less oil to carry heat away from the engine. Sometimes it can do that while oil pressure stays up. Along the same lines, blocked oil filter elements (which means the bypass activates and oil is dumped from the filter without going through the engine) can have the same effect.

Actually, the other thing to check would be the condition of the cooler and oil lines - it's not unknown for oil hoses to partially collapse or kink, restricting flow, while it's also possible for sludge to build up in the cooler and restrict the oil flow through it.

I've attached an image of the Aero-classics cooler... I'd estimate it, as oriented on the aircraft, to be about 8" wide, 5" high and 4" deep (fwd/aft). The transmission cooler (also shown) is much wider (left to right when installed on the aircraft).

Failing all that it might be worth calling here and talking to one of the real engine gurus instead of a soft-handed engineer! There's usually someone about from 7:30 am AEST (use time zone for Brisbane, Queensland, Australia).

Regards,
Doug.

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·         Russel Green

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Thx Doug I did find the inner-to-outer gear spec to be out of tolerance by .0015 inches. Measured .0045, book calls for .001-.003. Hard to believe that little wear is causing such a rapid rise in temp and loss of pressure, but I ordered new gears anyway.

I put the cooler and lines on a solvent stream yesterday-- sludge came out of the cooler right away. I'm now guessing this is the main culprit. Was the last thing I would have thought because I had that cooler cleaned & pressure tested 2 years ago. I'll be running some solvent thru the sump pan now. Also possible backing plate sealant was leaking, hard to tell when you take it off and old sealant is all chipped. Lines are stainless braided, so not kinked. Yes, cooler is a Positech model, although not finned on the ends like the one in your photo. Oil filter has been changed several times throughout the 1 1/2 years of this slowly building problem.

Very interesting and 'good' to know that pressure reading can be different than what the eng is actually experiencing. I'm now having some hope again.

A note here-- the gears arrived yesterday and are defective. The inner gear rotates thru it's arc just fine except for one high spot somewhere that binds the gear. Because there are 3 places that meet each time the lobes are 'tight', and because all same lobes are fine in the other orientations, I can't guess which spot to file. Nor do I want to file anything that is just fine with all other orientations. So now waiting on a replacement. Assuming these pump gears are made in AU, you would want to check to see if there is a bad run of them. Yes, I have both marker dots facing up.

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·         Doug Smith

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Sounds like we might be getting somewhere. Pump wear is very critical, I know once they get out of limits their performance drops off sharply.
I'll mention your issues with the new parts to the gents in the engine shop and let you know if there's anything to be learned there... let us know how you go with the next set.
Regards,
Doug.

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·         Doug Smith

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Hi Russel,
I spoke with Leith in the Engine shop and he confirmed my thoughts on that pump: the gears when delivered will almost always be sticky to turn by hand. Partially because the parts are new and tight, partially because when you're turning them by hand you can't hold the inner accurately in the right position.

It's totally normal and they work fine. Leith says it is possible to polish them with a scotch brite wheel so that they turn freely but that it's easy to go too far and wreck them: as i mentioned they're very very sensitive to excess clearance.

So, without seeing and checking your particular parts, chances are that they're "normal" and will work fine when installed.

Hope that helps!
Doug.

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·         Rob Turk

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Hello Russel,

Here's another thought, Doug may be able to confirm. Earlier engines have thinner through-bolts and lower clamping force, and may suffer from fretting of the case halves. When this happes, the Loctite seal between the two halves breaks and leakage from the oil passages strait back to the sump will start to develop. This usually results in lower oil pressure when hot and thin.

The elaborate fix would be to split the case halves, upgrade the through-bolts, polish away any signs of fretting (and hope the case halves are still servicable for bearing tolerances). Not an easy task, something you'd want to be done by a reputable Jabiru agent or Jabiru themselves.

The other option is to live with the fact as long as pressure and temperature stays within tolerances, and perhaps switch to a type of oil that maintains higher viscosity when hot. I've had good results with 15W50.

Rob

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·         Doug Smith

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Hi Rob,
Ha! We were starting at the easy fixes, trying to avoid splitting the engine! What you've described can absolutely happen, and fits the symptoms, but it's unusual on solid lifter engines like Russel's. I'm hoping the the couple of things Russel has found (worn oil pump, sludged-up oil cooler) will sort things out but if the don't... Ultimately tearing the engine down may be the only way.
Changing oil viscosity isn't a bad idea to try... Russel mentioned that he lives in a very mild climate so the W100 oil could definitely be a little on the heavy side. Older oil cooler adaptors had a little bypass hole in them so that if the flow through the cooler became restricted the oil could still get into the engine - so if the sludge Russel found was restricting the cooler too much the oil from the pump would effectively be bypassing the cooler, leading to the high temps. We deleted that hole from later engines and never looked back. It's possible to install a grub screw or similar to that hole to block it but you have to be super-careful that it never comes out; I used loctite 620 plus some brute force peening of the thread when I modified the one on my aircraft - it should never move!
Regards,
Doug.

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·         Russel Green

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Rob & Doug, thanks for your replies. This now is several times recently that a multi-visc oil has been recommended to me. My local OAT is about 24C and rarely above 27C in summer, 18C in winter, so didn't think a multi oil was called for. But I'll definitely try it.

I checked torque on my through-bolts at 480 hrs (520 hrs now on engine) and found 3 or 4 of them slightly under spec, all in the middle of the case. My A&P/Inspector & I could find no evidence of fretting but this sounds like the Locktite seal could still have ruptured. Since I will have already done 3 things at once (new pump gears, new Locktite on backing plate, cleaned cooler of sludge), I'm reluctant to add a 4th before testing to see if problem solved. I'd like to narrow the cause. I did buy the new thru-bolt kit awhile back, to install at some point, might be coming sooner than hoped.

Doug, the bypass hole sounds like plugging it would not throw off the testing-- it would not have been a root cause of the problem. So I may go ahead and do it now. How deep to drill the hole for tapping?

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·         Doug Smith

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Hi Russel,
It was all a while ago and it's one of those jobs where any one of several methods would work... from memory, I tapped the thread just deep enough so that when the grub screw was screwed in tight it ended up about 0.060" below the surface of the adaptor - enough that I could peen the thread in a few spots with a centre punch and be sure it was never going to work its way out. The grub screw I used was a short one - about 5/16" - so, depending on your tap, you'd have to run it about 0.4" deep.
Regards,
Doug.

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·         Russel Green

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Russel here: After installing new oil pump and cleaning out the oil cooler, I now have several test flights and a report to make. The old pump was 0.0015 inches out of tolerance; because Jabiru said that pressure falls off rapidly after tolerance is over, I replaced with new. The oil cooler (and hoses) were put on a pressure solvent stream; technician said a moderate amount of sludge exited in 1st few minutes. I also cleaned bottom of sump pan. With new pump and such, I removed the 2 washers from the back of spring in the oil pressure relief valve so as to make 1st tests be in factory new condition.

1st test was an 85 F degree day (29.5 C); change was very slight but did result in oil temp stabilizing in the green, but very high at 235 F (113 C); previously oil temp would keep climbing to redline so that I had to throttle back for landing; and to get the temp to stabilize @ 235 I had to cruise at 2500 RPM; pressure was low @ 35 PSI (16kg/sq cm).

2nd test was now much cooler weather that will remain for several months, unfortunately throwing off the test parameters. 60 F/ 16 C. I installed the max allowable number of washers in pressure relief valve-- 3; at 2500 RPM engine has 194 F/90 C and 36 PSI;
at 2800 RPM engine is 197 F/ 91.5 C, 39 PSI (17.5 KG PSC). So pressure is up to a low but acceptable range and the temps have stabilized in a good range.

3rd & 4th tests have reiterated the 2nd test. Slightly warmer day, slightly warmer oil temps; pressure remains as test #2.

I had an oil analysis done and they found no indication of bearing wear that would make for oil leaking past the bearing races and accounting for the weak pressure I'm seeing. With a new pump and still needing 3 washers in the relief valve, this is pointing to the original spring having lost it's tensile (temper) strength. So it looks like I had a Gang of Three come riding into town--- pump out of tolerance, cooler sludge, and weak spring. Yes, I've ordered a new spring, and for now I'm flying again.
Thanks for all your help.

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·         Doug Smith

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Hi Russel,
Great to hear you're flying again, glad we could help!
Regards,
Doug.

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