I'm now putting 20w50 in my Prius. Arrrrh!

I've been using 5w30 in my Prius for the past 8 years or so, and over that time the oil consumption has slowly increased as it's now pretty high mileage (312,000 km).

Recently I changed from an ACEA A3/B4 rated 5w30 oil (castrol edge A3/B4) to a more fuel efficiency oriented GF5/Dexos1 oil (Penrite Enviro+ GF5 5w30). Suddenly with the new oil the rate of oil consumption nearly doubled, from about 250 mL per 2000 km up to about 450mL per 2000 km.

Although they are both 5w30, the new oil is a fair bit thinner and has lower HTHS viscosity. As far as I can tell that's the only thing that is causing it to use more. Anyway, I decided to start topping it off with 20w50 and see if that would slow it down. Right now I'm up to about 750 mL of this 20w50 top off for this oil change and it seems to be working, the oil consumption is definitely slowing down.

Unfortunately I bought a few 5L jugs of this thinner oil so I've still got a couple of them to use up. I'm seriously considering blending the stuff with my 20w50 (at about 1 part in 4) for my next few oil changes.

 

Yeah but not a lot of choice it seems. I wanted to give "Valvoline Maxlife" a try in this engine but it's so hard to find here. Eventually I found it, but only the "semi synth" stuff in the red bottle, and only in 20w50 (seriously, no other grade here at all in that product).

At first I balked at it (as I haven't used 20w50 in anything for a long time), but then I thought what the heck - it can't hurt to blend some in as top off oil. Anyway, I've topped off a few times now and added about 3/4 of a quart of the stuff, and the last 2000 km it seems to have eased back to about 300 ml consumed which is an improvement.

 

Yeah I have read a few people's reports of success with Techron here. Do you just add it to your fuel, or do you have to do piston soaks or something with it?

I do usually run some injector cleaner through it (in the fuel) once or twice per year. Up until now I haven't been too worried about the oil consumption though, it wasn't ideal but at about 1L per 8000 km (5000 miles) it never bothered me.

 

I take your point SAM, however I'm talking about adding a relatively small quantity of the 20w50, perhaps 800mL per oil change. TBH, I've often used different brands of top off oil (like whatever I've got left over) in the past and I've never had any issues. As Austin Powers would say, "I like to live dangerously".

Manufacturers know that people will sometimes use a different brand to top off and they make them at least compatible enough that nothing drastic will happen. However I do take your point that it's not ideal.

CITGO.com, Consumer Products, Oils, Engine Oil Myths

 

Yes.

 

You've got the conversion a little out there. A litre is a little more than a quart, so it comes out to about 2.4 quarts per 10,000 km, which is the recommended oil change interval here.

Yeah I'm in a fairly high ambient temperature region here. Nothing extreme, but very likely to have multiple 100F + days over the next few months and unlikely to see much under 60F at all. So no real need for very low viscosity oils for me.

The increase in viscosity that I've got is nothing too drastic anyway. With what I've blended I'd estimate it still in the 10w30 range according to this widman calculator. See: Mixing viscosities | Widman International

 

Yes, same observation here SFO. High engine RPM (especially "B" mode in mountains) does seem to make it consume oil faster.

Up until this experiment I wasn't too sure what the effect of increasing viscosity would be, but now I know that (at least in my particular engine) higher viscosity definitely does result in lower consumption. I don't want to go crazy with high viscosity or anything, but I'm considering giving it a run on 10w40 over summer just to see how it goes (and in particular to see if I notice any change in fuel economy).

Yeah, I think they just like to have a nice round number, so 5k miles in the US and 10k km here in Australia. Did you know that in the UK they (Toyota) even specify a 10K mile interval on the Gen2 Prius.

Yes it's not a serious problem to me, but still I was happier when it was about 1.0 to 1.5L per 10,000 km.

At the moment, with about 750 mL of the 20w50 blended in, it seems to be back inline with about 1.5L per 10,000 km.