I have a Ford truck with a 2004 Caterpillar C7 diesel engine at 70k miles (play truck, F750 pickup conversion, mostly in-town driving). I had Rotella 5W-40 synthetic in it with no issues. After upgrading the turbo, injectors, and rerating to a higher power rating; I started to get an oil leak on the ground. I'm almost sure it's coming from the rear main seal. I definitely ruled out the blow by tube. I probably added 8 quarts on the Rotella. For this most recent oil change, I thought I would try a 15w-40 to see if it would slow the leak. I found that Amsoil had a full synthetic 15W-40. It has been about a year now, and I've only had to add about 3 quarts. My question is: Should I credit Amsoil as being a superior oil, or the fact that it's a higher winter viscosity? I'm planning my next oil change, and am highly considering trying a dyno 15W-40 to see what happens.
Rear main seal leak vs oil weight
- Thread starter zachakamp
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A leaking seal is mechanical damage from wear/age. Neither oil will 'fix' the seal.
As for your added oil 1 vs 2.. you would have to compare miles and time with both being equal.
Unless you are going for extended drains i dont see any need for high dollar synthetics in that C7. Any modern CK-4 CJ-4 15w40 is all that engine needs.
I would run supertech/rural king/traveller 15w40 and 'run it and watch it'.
As for your added oil 1 vs 2.. you would have to compare miles and time with both being equal.
Unless you are going for extended drains i dont see any need for high dollar synthetics in that C7. Any modern CK-4 CJ-4 15w40 is all that engine needs.
I would run supertech/rural king/traveller 15w40 and 'run it and watch it'.
It's a thicker weight oil. So it can't creep into small spaces as easily as a thinner weight oil. It's harder to pump. The flow isn't as good. Which means less oil can get past the seal. The same is true for the engine as a whole. The flow isn't as good between moving metal parts.
How did you rule out the crank case vent? You have increased the combustion pressures, there is possibley more blow by. Syn oil is a waste for other than below freezing starts or extended oil change intervals , especially in an engine with an oil leak. You can at your own risk try a mechanic in a bottle to see of it clogs up the leak. The proper fix would be to replace the seal and if possible use a shaft saver and make sure there isn't too much wear on the main bearings.
If a 15W40 doesn't leak much when hot, then it isn't the 5W40 cold properties that are causing your problem. Simply put, a 5W40 is NOT a thinner oil (except for the very brief time when cold, the 5W40 is thinner than what a 15W40 would be, but still it is thicker cold than either of them are when hot).
Now maybe the seals swell slightly w/ one oil vs another. Who knows.
Now maybe the seals swell slightly w/ one oil vs another. Who knows.
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I put a catch can under the crank case vent tube. It is perfectly clean.
Originally Posted by bismic1
If a 15W40 doesn't leak much when hot, then it isn't the 5W40 cold properties that are causing your problem. Simply put, a 5W40 is NOT a thinner oil (except for the very brief time when cold, the 5W40 is thinner than what a 15W40 would be, but still it is thicker cold than either of them are when hot).
Now maybe the seals swell slightly w/ one oil vs another. Who knows.
That's exactly what I'm thinking. Thus, my next oil change to be dyno 15w-40.
If a 15W40 doesn't leak much when hot, then it isn't the 5W40 cold properties that are causing your problem. Simply put, a 5W40 is NOT a thinner oil (except for the very brief time when cold, the 5W40 is thinner than what a 15W40 would be, but still it is thicker cold than either of them are when hot).
Now maybe the seals swell slightly w/ one oil vs another. Who knows.
That's exactly what I'm thinking. Thus, my next oil change to be dyno 15w-40.
My Volvo leaked a fair bit of 15W-40 and 5W-40, and coated the underside of the car with 5W-30. Now running 15W-60 and just a few drops after a long run, hardly a drop around town.
And yes, I've done the PVC thing, the glove test etc. I'm never doing the RMS on a $500 car.
And yes, I've done the PVC thing, the glove test etc. I'm never doing the RMS on a $500 car.
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