Fuel efficiency

I get about 20 miles to the gallon on my 1991 Hiace Cruising Cabin - 2.8 liter diesel.  THis is pretty much the same on driving around town and motorway trips, always trying to drvive with a light touch on the gas.  The engine only has 100K kilometres on the clock and seeems to run beautifully - okay very underpowered going up hills.  Searching on the forum some people think 20MPG is normal others expect 28-30 MPG.  Any thoughts?  Should I just put up with this?  Any suggestions?  It's not the turbocharged engine by the way.

The tyres probably don't help - they are Goodrich Mud terrain tyres.

I've got the same engine as you.  Around town I get 23mpg. If I am doing a lot of motorway miles I get up to 28mpg.  I've got 30mpg a few times but not recently.  When I first got the van (6 years ago) I used to have less of a heavy right foot and would cruise at 55-60mph and the fuel consumption was a whole lot better, averaging 25mpg.

I'm running some Avon Rangers (standard tread pattern), and have thought about getting some BFG's to pimp the van up but was worried about fuel efficiency and extra road noise so have held off for now.  

I hear you about uphills.  The engine really is a gutless wonder when it comes to hills.  Getting overtaken by lorries up hill can feel a little embarrassing at times, but I sail on past then again when it's downhill.

Automatic or manual? Automatic may take more.

20mpg is like 7.1 kilometers per liter? That is a bit poor.
I can also get that when Im driving "fast" on the motorway. But I can get better when driving a bit more relaxed.
Have recently managed 10 kilometers per liter but usually I don't get that. That was a lot of driving 80 Kph outside cities.

I had poor fuel efficiency lately and even smoking. Turned out my air filter was completely full of dust and sand (it has seen quite some bad roads)

Does it smoke a lot?

And what tyre size? Yeah the Mud terrains probably wont help. Pressure also makes a difference.
Maybe measure with gps a few stops to see how much your odometer counter is of.

When I get through some more tanks through I'll have a better idea of my MPG but it was around 30MPG drifting down the A1M from Newcastle at about 60mph.

As well as the aforementioned tyre pressure also check:

1. Tracking - wearing tyres takes energy
2. Engine oil, use fully synthetic - it's more slippery, especially when cold
3. Gearbox oil, pay more for synthetic (if changing auto fluid monitor the colour after the change as it may dislodge dirt you'll want to change out rapidly).
4. Diff oil, pay more for synthetic

Then it's just down to driving slower and conserving momentum.
Also consider running some fuel system cleaner through as deposits do build up, I have no idea which the worthwhile ones are however.

Sorry, I'm not sure if I agree that synthetic is more slippery. The numbers indicate how thick or thin it is. Like 0w30 is much thinner than 15w40. But I wouldnt suggest 0w30.
Right now I'm running 10w30, non synthetic, 10 euro for 6 liter. It just means quality is lower and it needs to be replaced faster.

Hiace4wd wrote:

Sorry, I'm not sure if I agree that synthetic is more slippery. The numbers indicate how thick or thin it is. Like 0w30 is much thinner than 15w40. But I wouldnt suggest 0w30.
Right now I'm running 10w30, non synthetic, 10 euro for 6 liter. It just means quality is lower and it needs to be replaced faster.

You are correct that Xw30 is thinner than Xw40 yes. (x = the cold weather equivalent viscosity).

Your 10w30 oil is made from SAE 10 oil, and they then add plastic micro-coils to it. This plastic unwinds as the oil heats up and prevents the oil from thinning out too much, so it gets the SAE 30 rating at 100C.

Synthetic 0w30 is also SAE 30 at 100 C, so at running temperature it's basically the same thickness, but there's no plastic in it: synthetic oil is 100% uniform synthesised oil and therefore very slippery and stable - including at very high temperatures. In general a PAO based synthetic is a huge step forward.

Your 10w30 has a lower shear strength and more friction (from that plastic) when new, and in use the plastic micro-coils get mashed up by the piston rings so the viscosity of 10w30 heads towards SAE 10 (very thin) during its lifetime and the plastic comes out as varnish which then coats the inside of your engine.
Incidentally this makes SAE 30 lawnmower oil a more stable choice for many applications than non-synth multigrade which always has this problem of plastic and a diving viscosity

Meanwhile as synthetic oil ages it just gets very slightly thicker, and because it's more mechanically stable lasts for far longer. Far far longer - limited generally by the need to change it to get the rubbish from the engine out of the way (soot and acids) rather than any issue with the oil itself. Synthetic oil has broadly stable viscosity over a wide temperature range which is why you get the crazy 0w value, it's not super thin when cold, it's just basically still around SAE 30 when cold so it flows fast and protects far better.

That lack of thickening of synthetic oil when cold is good for the engine but bad for any leaks you have - to beware drips on your drive.
BTW personally I wouldn't bother with semi-synth, it's just a cracked form of regular oil, always go for fully synth if you want the benefits. My van still has whatever they put in it in Japan but will get 5W30 when it needs changing as that's recommended by Toyota for my engine, bear in mind your's maybe only happy with 40 weight.

Some further reading, I've been studying oil for a while although many find the subject intensely boring

https://www.carbibles.com/guide-to-engine-oil/
https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1137824
https://www.bobistheoilguy.com/motor-oil-104/
https://www.oronite.com/products-technology/viscosity-modifiers/default.aspx
http://www.syntheticoilhq.com/fueleconomycomparisons.html

Well, this can be true, but two things.
I think it is not that big of a deal compared to driving behavior, tyres or indeed old oil in gearbox or diffs.

Funny as it as, I have now gotten my best fuel efficiency during our long trip on tge non synthetic oil
But the others were half synthetic not full. Probably it is a coincidence.

Second, the old diesel make the oil black in no time. This is also breaking down the oil.
Because of this I prefer to change oil every 5000km and usually buy the cheapest oil.
As I mentioned once before, in my petrol Yaris I had synthetic oil for almost 70.000km

Agreed, on a well seasoned diesel it is indeed a compromise between rapid changes to get the dirt out and the cost of the oil, no use saving a few pounds on diesel to spend it on oil . A quality filter also makes a difference.

I discovered synthetic Westway oil is cheap enough in the UK to use - cheaper than driving to the motor store to buy non synthetic so for me the decision is easy.

E.g:
https://www.ebay.co.uk/itm/5L-Westway-Audi-VW-LONGLIFE-3-Oil-5w-30-5-Litres-504-507/111563191424

Oil discussions tend to be quite esoteric, and while people are still fretting over the details their vehicle has rusted away, been crashed, stolen or simply replaced.

Your Yaris point is interesting in another respect: Diesels give more MPG but eat more money in servicing!!

Well, it is certainly true that newer diesels have higher maintenance cost than petrol. But with my old Hiace I wouldnt know where to spend the money on maintenance.
Now on our long roadtrip I buy oil for about 10 euro, and I brought an oil filter. I replace the oil every 5000km and the filter 10000km.
I just do it myself because it is quite easy, especially when you don't do the filter.
So quite cheap, actually buying a new air filter was a whopping 40 euro and doubled servicing costs for a while

I think old diesels should always be cheap to run, but the new Euro 6 is not going to be any cheaper than petrol.

If I invest in a newer van I'd wait until a decent petrol hybrid is available, too much to go wrong on a modern diesel!

Toyota has quite some huge MPVs like an Alphard which are almost as big as a Hiace. They come with a petrol hybrid drivetrain. And 4wd.
But I like the RZ engines. The hiace 4 with engine in front can come with a 150hp 3RZ petrol. A simple engine, and so it runs on crap fuel with low octane as well (this is great for outside Europe)

Anyway, we are totally off topic now.

I found this thread about fuel efficiency if it's any help:

https://hiace-super-custom.forumotion.com/t1144-fuel-economy

I suspect if you need 40 MPG the only way is to buy a Renault Trafic 1.6Dci, the Hiaces are good if you get 30 MPG but don't be surprised if you end up with 15-20.

There's an interesting post in that link, someone drives super carefully and gets 35 MPG, up from 20 - so maybe some super-careful driving may be worth it.

Outside of the Hiace the word on the street is that the injectors themselves are fairly important for MPG, and also air filters. Interestingly the 1kz-te has a throttle which IIRC is unusual on a diesel, not sure how that design affects the MPG compared to the later more efficient D4D.