Oil cooler failure

[nitrohog]

I have had two oil coolers fail on my new to me IO360 powered RV-4 this flying season now and I am looking for advice on what to inspect/ possibly change.
The first oil cooler was a Stewart Warner 7 row that came on the airplane when I bough it. It looked a little scruffy, but it did it's job well until I put about 10 hours or so on the airplane. Then it sprung a leak at the top "tank" seam in between two of the rows. I replaced it with the same make/ model that was a Drake air overhauled unit that had been on the shelf for several years. I put about 25 hours on this one and it failed in close to the same location, this time leaving me stranded 100 or so miles from home.

For reference, the cooler is mounted to the rear baffle, the AN hoses have plenty of flex and aren't pulling on their fittings at all, and I had the prop dynamically balanced the day prior to the second failure (I highly doubt it is related at all, I just wanted to state that the second one failed after it was balanced). Oil pressure is about 80PSI in cruise and never exceeds redline. Oil temp is consistently around 180F in cruise.

Am I just unlucky or is there a contributing factor that I may be missing?

 

[PaulvS]

How is the oil cooler attached to the baffle, i.e. how many bolts, which locations, are there tubular spacers of the correct length on the bolt shanks etc.? If you can post pictures of the installation then that might help to get help.
(i don't know anything about that particular brand of cooler or its rating.)

 

[Dan 57]

cooler is mounted to the rear baffle

Which is what Vans recommends and depicts on their plans/manuals, but per se not a good idea. A relocation to the firewall using quality hoses of the right length and supported correctly will guaranty a long and trouble-free life for an oil cooler.
Recently replaced may 2.3Kh/25y Positech with AAVID Niagara, same location and brackets, air shutter installed on top.

 

[Kyle Boatright]

As stated, pictures would help. Out of curiosity, what is your typical oil pressure on a cold start and during flight?

 

[mcgaughy]

I have had two oil coolers fail on my new to me IO360 powered RV-4 this flying season now and I am looking for advice on what to inspect/ possibly change.
The first oil cooler was a Stewart Warner 7 row that came on the airplane when I bough it. It looked a little scruffy, but it did it's job well until I put about 10 hours or so on the airplane. Then it sprung a leak at the top "tank" seam in between two of the rows. I replaced it with the same make/ model that was a Drake air overhauled unit that had been on the shelf for several years. I put about 25 hours on this one and it failed in close to the same location, this time leaving me stranded 100 or so miles from home.

For reference, the cooler is mounted to the rear baffle, the AN hoses have plenty of flex and aren't pulling on their fittings at all, and I had the prop dynamically balanced the day prior to the second failure (I highly doubt it is related at all, I just wanted to state that the second one failed after it was balanced). Oil pressure is about 80PSI in cruise and never exceeds redline. Oil temp is consistently around 180F in cruise.

Am I just unlucky or is there a contributing factor that I may be missing?

I'd call Pacific oil cooler and talk to them today.....and probably buy next cooler from them. Obviously you've worked on vibration and hose stress. Curious what the "ips" was prior to balancing..... others have pointed out mounting and there is also the issue of baffle flexing. Look over your baffles carefully for cracks / breaks. Sorry can't be of more help. Partnering with Pacific might be your best bet if all your baffling looks good. By the way, there's a post somewhere in vansairforce about adding a reinforcement strip on the oil cooler flanges (both sides) like Grumman American uses on their AA5B. I own a Grumman and agree it's a good idea so I used this on my RV7a.

 

[D-Dubya]

Is it possible that the cooler may have been stressed when tightening the hose fittings? If you're not holding backup with a wrench on the flats (or hex nut) welded into the cooler when attaching the NPT hose fittings, it could be putting undo twisting forces on the cooler case.

 

[lr172]

Is it possible that the cooler may have been stressed when tightening the hose fittings? If you're not holding backup with a wrench on the flats (or hex nut) welded into the cooler when attaching the NPT hose fittings, it could be putting undo twisting forces on the cooler case.

+1

It would seem that the cracks are happening in an area that could be from this kind of stress. It takes a bit of finesse to ensure that ALL of the resistance is being countered by the wrench on the thread base. That said, I expect many amateur builders are not so carefull here and doesn't result in a leaking cooler. A tip for the future is to NOT tightening the fitting with the cooler secured to anything. Just lay it on the bench/floor while tightening. This ensures that all the countering effort will be from the wrench on the thread body and not from the cooler body.

It is also possible that you are just unlucky and the two failures are not related to anything but flaws waiting to make a leak. There are A LOT of RVs with coolers mounted on the baffle and very few folks report here that their cooler sprung a leak; Baffle cracking, yes, cooler cracking/failure, No.

 

[nitrohog]

Thanks for the replies so far.
-The startup/ idle oil pressure is around 60-70PSI depending on temp. In cruise it stays slightly above 80PSI.
-I agree wholeheartedly that the oil cooler would be better suited on the firewall, but I honestly don't know if that is a viable option in the incredibly compact RV-4 engine bay.
-The engine vibration started out at .66IPS and we got it down to .05IPS I believe.
-I don't believe that I stressed the fittings during install, I did back them up when tightening.
-I like the idea of the Grumman style reinforcement and I will be incorporating that in the future.
-The cooler is mounted to the baffle with 4 bolts through the baffle, I will attach a pic of the old cooler (its all I have). I think this may be where the "smoking gun" appears. After review of the pictures, the old cooler had one of the flanges shaved off of it, so the spacers and long bolts were only on the outside of the oil cooler. I may have mirrored that when I installed the new cooler.

 

[FlyerJim]

Holy crap, that is not right for sure.
I have a certified plane that has 6,000 hours on the oil cooler. It was a flight school plane that put 5,000 hours on it before they sold it out to the private market. I say that to point out that I would have replaced the oil cooler, or at least overhauled it, at each engine rebuild, but they did not. I have a new one ready to go for when I can get an A&P to do my engine swap.
I cannot find ANY records of any problems with the oil cooler in those 6,000 hours.
O-320-D2A in a Socata Tampico.

 

[johnpaul44]

Thanks for the replies so far.
-The startup/ idle oil pressure is around 60-70PSI depending on temp. In cruise it stays slightly above 80PSI.
-I agree wholeheartedly that the oil cooler would be better suited on the firewall, but I honestly don't know if that is a viable option in the incredibly compact RV-4 engine bay.
-The engine vibration started out at .66IPS and we got it down to .05IPS I believe.
-I don't believe that I stressed the fittings during install, I did back them up when tightening.
-I like the idea of the Grumman style reinforcement and I will be incorporating that in the future.
-The cooler is mounted to the baffle with 4 bolts through the baffle, I will attach a pic of the old cooler (its all I have). I think this may be where the "smoking gun" appears. After review of the pictures, the old cooler had one of the flanges shaved off of it, so the spacers and long bolts were only on the outside of the oil cooler. I may have mirrored that when I installed the new cooler.

Idk if the vibration caused your oil cooler failure but .66ips is alot honestly. I expect when you balanced to .05ips you felt a big difference ?

 

[fixnflyguy]

I have my RV-4 mounted on back baffle. My oil pressure is near 100 on cold start-up, 85ish in normal flight. Your failure certainly sounds like its vibration, or loaded under stress. here is my installation. make sure the bolts that mount the cooler pass through both sets of flanges, with a proper length spacer in between; failure to put the spacers in will likely result in cracks. . Also, make sure your baffle is supported well with robust angles, and a tie rod that keeps the assemble from flexing the baffle. It doesn't sound like your fitting bungs have cracked, but make sure they are not overtightened.

 

[nitrohog]

Idk if the vibration caused your oil cooler failure but .66ips is alot honestly. I expect when you balanced to .05ips you felt a big difference ?

Not a ton honestly. It is smoother but it really didn't feel terrible before.

I have my RV-4 mounted on back baffle. My oil pressure is near 100 on cold start-up, 85ish in normal flight. Your failure certainly sounds like its vibration, or loaded under stress. here is my installation. make sure the bolts that mount the cooler pass through both sets of flanges, with a proper length spacer in between; failure to put the spacers in will likely result in cracks. . Also, make sure your baffle is supported well with robust angles, and a tie rod that keeps the assemble from flexing the baffle. It doesn't sound like your fitting bungs have cracked, but make sure they are not over tightened.

That looks really nice! I think I'll incorporate some of your bracing ideas into mine.