Synth back to Mineral

[RETIDEPXE]

Any problems changing back to mineral from Synth. Have heard it creates problems in gas engines, may be old wive's tale or different for diesels?

Reason being, oil pressure seems too low on my Cat C-9, around 37psi at 1500rpm cruise and 15psi at idle when fully warmed up. In a pull up a hill it drops to around 32psi at 1400rmp. Oil pressure was 7psi or so higher w/ mineral oil. I tried adding a gal of Lucas but heard it causes cavitation afterwards and oil analysis showed a small spike in iron content so changed oil and did not add Lucas again.

Other reason is the cost of synth since my motor drinks a gallon (no leaks) every 2500 mi.s. I wonder if anyone has had valve guide seal problems on Cats or is this more then likely a cyl/rings wear issue? Oil analysis from OPS recommended lab in Houston has been virtually normal for last 150k mi.s, motor has tot. of 373k mi.s. I have maticulously maintained the motor since I bought it as a repo w/ 73k mi.s, can't speak for first 73k so could have had a hard breakin to say the least.

Any comments, suggestions appreciated,
Reitedepxe

 

[Turtle]

Every time you change types, viscosities, or brands of oil, the change causes the engine to wear a little differently. Switching back and forth between types (synthetic and dino) is the more significantly dramatic of the changes, being a gas or diesel engine. I would change types as the last resort, and would change viscosities first, either from within the same brand of oil you have been using or an engine-manufacturer approved additive. Actually, first thing I'd do is try to determine why it's a low pressure. Could be wear, a seal, or a pump, or even a sensor with some engines. It's best to pick an oil and stick with it, forever, same brand and viscosity. If you routinely change brands or viscosities, then it's likely a wear issue. Once you know the cause, you can better deal with the problem.

 

[piper1]

I wouldn't worry about those pressures. The C-9 is supposed to cruise at 1600rpm...so with you running a tad slower (which is OK) you will see slightly lower oil pressures. The difference in oil pressure between the synth and the conventional oil is pretty normal, that's one of the reasons you get (or should get) better mpg's with a synth oil.

 

[greg334]

Iron wear?

May be thrust journal wear. How much of a spike?

Other than that, I'm with Piper and Turtle.

 

[skyraider]

Every time you change types, viscosities, or brands of oil, the change causes the engine to wear a little differently. Switching back and forth between types (synthetic and dino) is the more significantly dramatic of the changes, being a gas or diesel engine. I would change types as the last resort, and would change viscosities first, either from within the same brand of oil you have been using or an engine-manufacturer approved additive. Actually, first thing I'd do is try to determine why it's a low pressure. Could be wear, a seal, or a pump, or even a sensor with some engines. It's best to pick an oil and stick with it, forever, same brand and viscosity. If you routinely change brands or viscosities, then it's likely a wear issue. Once you know the cause, you can better deal with the problem.

If u will log on to bobistheoilguy.com u will find out more about oil then u will ever want to know,,cars trucks and 1 8 wheelers.

 

[Turtle]

If u will log on to bobistheoilguy.com u will find out more about oil then u will ever want to know,,cars trucks and 1 8 wheelers.

Yup. I'm there often.

 

[davekc]

Your biggest issue based on your post is using a gallon of oil per 2500 miles of driving. That is high. I would recommend doing a cutout on that engine and possibly a compression test. Even though it isn't leaking on the ground, there could be several places you are having issues.
Internal leak at the Huey pump, bad rings, or a leak at one or more of the injectors. All will increase oil consumption without the appearance of a leak. Even a leak at the turbo will fit your symptoms although not as likely. A good Cat dealer should be able to narrow it down pretty quick. Most truck dealers have parts changers verses actual technicians, thus the recommendation of going only to Cat.

 

[RETIDEPXE]

Thank you for all the info.

Gregg, my iron was as high as 17ppm before Lucas then went to 34ppm in 12k mi.s after adding the Lucas. When u say thrust journal are u referring to crank oil journals?

Dave, I plan to get it into Cat for the oil usage. I was told the preverbial 'within specs' over the phone from a Freightliner Dlr. Oil analysis shows soot vol. staying at <.1% but nitrate is around 19-23ppm. Blowby?. I have a good Cat warranty on the motor plus option for turbo and injectors, plan to get to a Cat dlr next trip home. Will report back afterwards. I too think a gallon/2500mi.s is a bit much.

Retidepxe

 

[greg334]

I'm referring to the wear on the connecting rods surface that ride against the a face cut into the crank. Some times I have seen where the oil pressure is lower then it should be and there is a high iron content in the engine oil which turns our to be a higher than acceptable clearance between the rod and the crank. If the journal losses oil pressure, the bearing rubs the journal and you end up with high lead content in the OA and a need to replace the bearing sooner than later - especially under pressure of making torque.

It seems to be a common problem not with trucks as much as it is with cars. Doing a lower end on a truck the mechanic needs to check the clearance but a few times watching them, they don't.

 

[RLENT]

Gregg, my iron was as high as 17ppm before Lucas then went to 34ppm in 12k mi.s after adding the Lucas.

Yeah ... if you go up to the forums on bobistheoilguy.com, in the oil analysis section, there is a virgin analysis done on Lucas .... bottomline (as I recall), Lucas was really great ... if you wanted to thicken up your oil .... beyond that there was very little else in it to be of any benefit to a lubricating oil.