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midairmark January 11th, 2019 13:16

Idiot me, put in wrong oil month ago, OK to leave?
Well I screwed up my last oil change, didn't look at the label and put the wrong oil in. I usually use Mobil 1 full syn. truck diesel, 5w-40. I had a lot of my mind about having a car transported and just picked up the wrong container. I put in Mobil 1 full syn. 5w-30 for the wife's gas car. I didn't notice until today, when I went to change her oil and noticed I had a full gallon of diesel oil, unopened!

I have been driving the car at least 3 weeks with that oil in it. I don't beat the car, just transportation and I don't rev it higher than 2500 usually. It has 237k miles on it, 01 Jetta.

Do you think I need to change the oil out or do you think it is OK until next oil change?


KLXD January 11th, 2019 13:21

You know what they say about opinions but here's mine: Drive it.

Before I knew better I used plain ole 10-30 in my '98. Prolly for at least 50k. It's now got over 350k.

1.4TDI PD January 11th, 2019 14:09

I think you will be just fine. In the long run you want to put 5W-40 but once or twice shouldn"t do any damage to your engine i have been runing 5W-30 on a couple of engines before i realized i should switch to 5W-40 to minimize engine wear. And they are all still runing strong.

midairmark January 11th, 2019 14:49

OK, thanks guys.

turbocharged798 January 11th, 2019 17:02

I would get that oil out ASAP. It not rated for compression ignition engines and cannot handle soot. It will cause very high engine wear. The 30wt will not do the flat tappet cam any good either.

Owain@malonetuning January 11th, 2019 17:34

I'd swap it, probably won't do much harm but no sense risking it. On the plus side I guess that counts as an engine flush.

VeeDubTDI January 11th, 2019 17:47

Add me to the "change it" camp.

Mongler98 January 11th, 2019 17:53

yea, before i found this site, about 2 full years, maybe 95K of just cheep full synthetic 5-30 in what ever gave me the biggest rebate.
your fine.
In fact you could keep useing it, but im a stickler and would insist you change it out back to 5-40 diesel mobile one on your next oil change. dude your fine.

flee January 11th, 2019 21:58

I did the same thing with some Mobil1 non-diesel oil. I just sucked it out and kept it
to top up our various gas burners. There may be a quart or 2 lying around here still.
I only drove about 45 miles on it and so I didn't want to waste it.
Didn't bother changing the filter.

AndyBees January 12th, 2019 04:38

I avoided chemistry in HS and college.... and may have stayed in a Holiday Inn last night.

Having said that, here's my opinion.

Today's modern full synthetic oils rated for gasoline engines are likely much better than what was dumped into diesel engines 50 or 60 years ago.

The immediate concern is the Turbo shaft........ don't want any coking. However, I suspect the gasoline rated synthetic oil can handle that heat as it probably meets specs for the VW 1.8T which runs a hell of lot hotter than any TDI Turbo.

Yes, like KLXD stated and others, I did the same thing in the 40k to 50k mile range with my 2000 Jetta...... fast forward to the present. My son now owns it and it is doing just fine with over 370k miles on the clock.

Handling the soot just means the oil keeps it in suspension, thus no to very little settling out............ hey, what's that filter for?

Yes, I'd likely change that oil out a little sooner than normal ........ then drive more and worry less!

midairmark January 13th, 2019 08:00

Thanks for the input.

andreigbs January 14th, 2019 09:37

I'd consider it an engine flush type of oil ;) and replace it with the proper full synth diesel rated oil, then motor on.

midairmark January 16th, 2019 17:39

How about adding a diesel oil additive, to give the current oil additional protection aka Slick 50 (for example), instead of changing it out? What is recommended as a good oil additive?

jettawreck January 16th, 2019 18:37


Originally Posted by midairmark (Post 5474872)
How about adding a diesel oil additive, to give the current oil additional protection aka Slick 50 (for example), instead of changing it out? What is recommended as a good oil additive?

No. Resist the urge to overthink it. Leave it be or if it bothers you, change it. But leave the "additives" out.

turbobrick240 January 16th, 2019 18:50

Yeah, forget the slick50. You could get a quart of mobil1 15w50 for topping up though. That would thicken up the 5w30 and add some zinc. It's a tough engine, just keep it full of oil and you'll probably be fine.

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