Originally Posted by rwilson8272
7qt M1 5w-20 & Mopar filter every 3500mi
Can anyone explain the why it's ok to run synthetic oil for >4000mi?
I understand synthetic oil is less susceptible to thermal breakdown. What I don't get is the dirty aspect? My oil is nasty @ 3000mi.
Dirty oil is a function of the filter efficiency. While I was in warranty, the MOPAR filter / dealer oil would start to get dirty about 3.5K miles and be black by 5K miles.
Generally, oil does not break down that fast, but the additive package may. Synthetic oil is a more consistent makeup so the effect of any breakdown has less overall effect. However, I am not expert in tribology and learned this oiver the years. Sea story: I spoke with an Exxon port engineer who never changed the oil in his new (at that time) Lincoln Continental. What he did do was change the oil every 3K miles and add a quart of fresh oil. He analyzed the oil that came out at every filter change and claimed to have no engine wear indications after 75K miles. Then again, he had free access to an oil analysis lab..............
HEMI is now on its first run with a K&N filter and 5W-20 Castrol Syntec full synthetric oil at about 4K miles since the oil change. Checked oil level this morning and it appears cleaner than before. HEMI tick is greatly diminished. Will need to wait for next oil change to verify initial indications.
If you change oil/filter within the Jeep requirements, it probably doesn't really make too much difference.
The greatest engine wear occurs at startup anyway and more specifically during cold starts. If your driving involves lots of short trips and frequent engine stop/start, it's probably where most of your engine wear would come anyway. Using an oil filter with integral backflow preventer (i.e., check valve) keeps the oil higher in the system and minimizes the time for the oil pressure to reach the upper oil galleries and valve train.
Stationary diesels and marine diesel have a heater and pre-lube pump to prevent this startup wear (until the engine-driven lube oil pump builds up discharge pressure). This setup would be impractical on a car engine.