jct61765

I asked this question a while ago. This time I'm going to ask it different. I've put about 3000 miles on my truck since March. I used mobil 1 synthetic. Is it ok to use synthetic in an engine not used much. I drive the truck usually once a week for a couple of hours running errands etc. should I be using regular oil? I like the idea of changing my oil once a year.

KZN185W

iTrader: (1)

I see no problem with using synthetic oil for a seldom-used vehicle. Anyway, you plan on changing your oil at least once a year. Of course it would be cheaper if you use regular oil. But then again, changing oil only once a year will not result into big savings.

DaveInDenver

I'm not sure that it makes much difference. The problem is letting a truck sit long term with used oil, but you drive it once a week. It this case I would follow a timed oil change and not a mile-based one. IOW, something like an oil change every 3 months rather than 3000 miles. Make sure when you do drive the truck, to get it warm and avoid too many quick trips. A good long drive with the truck at operating temperature should help to evaporate moisture that will have accumulated in the oil. This will have the added benefit of making sure you get a good charge on the battery and get lube slung all around in the tranny and axles (moisture there is also important to get rid of). Otherwise, I wouldn't worry too much about it. There are different opinions on what to use, crude or synthetic. I've heard that synthetic can break down and seperate when left sitting, but it sits on the shelf sometimes for a while and it seems OK. So I think that's an urban legend. Crude based oil is supposed to be bad on seals when left sitting, but that also sound bogus to me. I'd think the only advantage synthetic really has in your case is that it might flow faster on start-up. Since in a week the oil will have all drained, that might be something worthwhile. Personally, I'd do a 3 month oil change with Castrol GTX and not worry.

jct61765

Mobil1 says 1 year or 15000. I am planning on changing it again this month. It is a little expensive, but for all of you with the 3.4 you know what a pain the oil filter is to get off. I was just wondering about the accumulation of gasoline in the oil. I do get it hot, the closest store is about 15 miles away.
Thanks

Beartracker

Don't mean to get off topic here but how does gas get in the oil? The reason I ask Is because last week I tried to start my lawn tractor with a 20 hp Briggs and oil and gas shot out of the carburator. Smelled the oil and it was full of gas. Drained the oil and turned the engine over a few times with out the plugs to blow it out.Cleaned things up including cleaning the plugs, filled with new oil , replaced the plugs and it started and ran like new.
Never had that happen before, Mike

Nic

Your carb float may be sticking allowing gas to accumulate on top of your piston. It seeps through and gets in your oil.

Beartracker

Thanks Nick, Never thought of that. Mike

Chainlink

From my understanding, synthetics dont break down or seperate like conventional oil (including slightly contaminated) and this is one of the main reasons to its 15000 or 1 year in engine shelf life. A mechanic I trust told me the biggest reason to run it isnt the viscosity from the intial oil change but its abilty not to break down with contaminates. Hence viscosity stays good through out your planned intervals(with in reason). He did add it will eventually break down but it takes alot of wear and contamination. But we are comparing crude to full science engineered.

I switched to Castrol full syn when it came out with no regrets whats so ever in all my yotas even one with over 200k on the odometer and it loved it. I change my oil every 7500 and it looks like I just changed it. My wifes rig has mobil one and seems like the results are the same( but for me nothing but Castrol ).

DaveInDenver

Both synthetic and crude-based oil is changed primarily because the additives are depleted and the oil contains suspended contamination, not usually because the base lubricant is broken down (yet). But, all oil will eventually break down. It's because the additives have been all used up and the oil then quickly begins to oxidize at the boundary state. This is not unique to crude oil, all oil would break down without all the additives. FWIW, don't think for a minute that something like a GTX is much less engineered than a Mobil1. The difference is that base lubricant in a synthetic comes from a non-mineral base that is synthesized from typically paraffin. After that, the two oils are usually more similar than different. Now the base oil IS very important, but the modern oils that come from refined crude are really quite advanced and will do a fine job lubricating your engine.

While the marketing says you can extend the change interval, it's not a good idea to do so without at least doing a used oil analysis to see what's going on. I found switching from GTX to Syntec that my interval could not increase and the switch to Mobil1 only allows a small increase. At first, this seems wrong, but both GTX and Syntec are Castrol and so probably share similar additive formulas. In all cases, the oil will rely on additives under extreme conditions where the oil is no longer in its regular lube state, but where it experiences heavy shear force (i.e. like when it's squeezed going through the oil pump or on rod/crank interfaces), to cushion the two wear surfaces. So the additives in GTX and Syntec are probably similar and why I could not get longer service life. Might be that since Syntec is not a PAO-based oil that it's shear is not that much better than GTX, who knows? I do know that in my engine it is barely better.

Still, I follow at most a 4,000 mile interval between changes on Mobil1. My engine is 179K mile old and most of my analysis showed combustion byproducts (mostly carbon and some ash), dissolved fuel and dirt were contaminating the oil. The wear numbers (oxidation and viscosity of the oil itself and suspended engine metal) didn't look bad and those would indicate a slightly longer interval is OK (although I don't suspect a massively longer interval with the fuel and ash levels). It also helped a lot when I threw away the K&N filter and went back to a factory filter, the silicon numbers went down significantly. Anyway, before leaving oil in beyond what the factory calls for, check the oil itself and see if it's wise to do so. Even the factory specified interval might be too long depending on lots of things. If you're driving in the desert with lots of dust and sand, then I certainly would never leave an oil in for 7,500 miles. But a relatively mostly pavement with a new engine, broken in well with a good, clean intake system could certainly go 10,000 miles on good oil.