I have an 87 Coaster and get around 7.5 kms to the litre. I think you will find the 3B engine is not turbo charged.

Ok the old issue,, speed versus economy eh.

We have 4.2l Turbo Landcruiser ute towing 3t van with all up mass of about 6.5 tonnes. If we "push" the speed we markedly increase fuel consumption BUT if we slow down by 10k or so we have much better fuel economy.

Having said that I hate "dawdling on main highways" so take mainly secondary roads and slow down (and we smell the roses).

So what can you do? You have some advice already BUT if the engine, driveline AND tyres (fully inflated and wheels aligned) are not 100% you lose economy.

Also get the engine specs - but we really need the engine prefix number but I found this:

The 3B is a 3.4 L inline 4 eight valve OHV diesel engine. Compression ratio is 20:1. Output is 90 hp (67 kW) at 3500 rpm with 160 ft·lbf (217 N·m) of torque at 2000 rpm.

These above were in BJ model SWB Tojo's in the 70's and fuel consumption was terrible, especially if over revved.

However you need to look at engine number perfix to ascertain the exact specs and with diesels you need to look at when the torque develops (ie start to rise) and when its at near maximum and then drive to achieve best results - the MAX torque above is 217nm AT 2000 rpm.

Hope this helps

Geoff

that is useful info you provided. I think you are on the right track in looking at the whole engine (not so much as fuel additives at this time). No smoke indicates that the engine is reasonably well tuned but I would take it to a diesel expert if it has an aftermarket turbo fitted to make sure the boost etc is correct.

On a dynomometer would be good also to find the torque range but this could be costly.

However you should be able to easily get the "feel" of when the torque "kicks in",,, ie drive into say 3rd gear normally and then accelerate smoothly and continuously, see if you can feel where she wants to pull and note the revs and then see where the power starts to taper off. On a slight incline is good for this.

You will then at least have an idea of what rev range to drive in. The most important thing for diesel economy apart from design and tuning is to drive in the rev range to give you the best combination of torque and economy.

As a LAST resort drive at different revs - ideally on flat terrain (outback QLD/NSW there's heaps of it) for say 200km and try to keep the same revs at all times (as far as possible). Top up diesel carefully/exactly using the same method and work out usage. Do this again but say 250RPM higher and then again at say 250 RPM higher. You should see a trend emerging either better economy or a worse economy. Repeat at higher revs if need be.

Hope this helps Cheers Baz