Oil question - cars.

Evening all,
Quick and perhaps stupid question, but can I mix 5w40 oil and 15w40 as I have some of each in the shed and the 1.5 Dci (diesel) Renault Scenic I just bought needs some oil?

Halfords website says it takes 5w40, is that right?

Third and final question is how should I check the oil, cold or warm?

Thanks all.

[Sid Squid]

Despite the catastrophe stories and end of the world scares some will recount when you mention this, you can mix the great majority of oils, there are a few mixes that are a complete no-no, but those two will be fine.
However, if the car is intended to run on 5W* oil then 15W is quite a bit thicker than it should have, and as the 5 and 15 refer to the viscosity when cold then the oil flow could possibly be compromised at exactly the point at which it is most critical - a cold start. Also is it intended to have fully synthetic oil, and is the one you're intending to use not so?
That said as long as you just want a top up and the amount you add is small, I'm sure it will be fine, and the bottom line is always that any oil is better then none**.





*I'm not saying it should or shouldn't use 5W, I haven't the foggiest which it should use.
** Unless you've filled your motor with Castrol R - but I doubt that.

Sids right don't worry, oil is oil I've been shouted down for this before but it dont matter a damn what you put in some is better than none and in a derv it makes next to no odds anyhow.

mmmm 5w40 sounds like fully synth and 15W40 sounds like semi syth.

Plus modern turbo charged diesel engines are quite dependant on the oil, they rev high now.

Put it this way for the price of new oil vs a new turbo I wouldnt.

I had a Mazda 5 Sport Diesel that when I bought it I trusted that the oil had been changed as per the stamp in the service book 10,000 miles later a new turbo was needed as the oil had broken down.

[Bibio]

don't worry about it for 15w to get to thick it would have to go below -10c.

Was only really using it as a temporary top up until i get it booked in for a mini service this week.

So sounds like it would be ok.

[NTECUK]

1.5 Dci we have in our dealer cars.
We have had a few at 55-70 k drop a big end.
Personally on those experiences I would not risk it.
They have split big ends ,so even if you caught it quick they are major heart ache to do.
If it Has a DPF you must use "Low Ash Oil" as it blocks up faster you if you use low quality oils.

Had enough fully synth 5w40 oil to top it up will get it in for an oil change this week.

The thing drives ok.

When I turned it on this morning the oil said level was OK.

Dipstick was filth though and the oil is black.

[NTECUK]

We use a semi synthetic oil,low ash.
If you push the mode switch (clock mpg etc)
It should show you an electronic dipstick representation.
Don't live and die by it though.
Check level after a refule stop.
Its warm on the flat and settled after that.
Keep an eye on the cam belt .