Optimum Rev Range Query - Hilux LN106 (3L engine)

Submitted: Wednesday, Aug 07, 2019 at 08:55
ThreadID: 138887 Views:5862 Replies:4 FollowUps:6
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Hey guys,

I've put about 15,000km on an old 2.8 diesel Hilux (1989) and wanted to find out whether I'm driving it as it was intended to be driven! Never owned a vehicle like this before.

I read on a forum that being an old diesel, I should keep the revs above 2000 in 3rd, 4th and 5th. Revving below 2000 is a no-no unless in 1st, 2nd or reverse. Is this really the case? I've kind of become used to cruising around in 4th down a hill or on a flat at 1500 and staying in 5th until about 1600-1700... Am I inadvertently damaging the engine by doing this? I've changed my driving style in line with the above since yesterday, but I'm not sure if it's necessary. It's a lot noisier in the cab now! Also, I tended to upshift around 2500 and downshift around 1500; I've increased these figures by 300rpm or so since yesterday.

I intend to keep this vehicle indefinitely and am trying to get as long a life as possible out of the engine! Looking forward to hearing what you guys think.

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Reply By: Athol W1 - Wednesday, Aug 07, 2019 at 09:26

Wednesday, Aug 07, 2019 at 09:26

Having driven a number of these vehicles, and done transmission repairs on a few, I would suggest that your current rev range would not be too far off the mark, however I would recommend that you do NOT regularly drive the vehicle in 5th gear below 2000rpm, or 80 kph, whichever is the highest of these 2 speeds.

As 5th gear, being an over drive gear and also containing the smallest gear in the transmission, tends to suffer from the torsional fluctuations that naturally occur with low engine speed. I have seen a number of 5th gears with broken teeth in these vehicles that were regularly driven below 80kph in 5th.

AnswerID: 627094

Follow Up By: David Y5 - Wednesday, Aug 07, 2019 at 09:53

Wednesday, Aug 07, 2019 at 09:53
Thanks for the detailed response, Athol. It's given me peace of mind!

FollowupID: 901073

Reply By: RMD - Wednesday, Aug 07, 2019 at 13:55

Wednesday, Aug 07, 2019 at 13:55
Besides the driving style, if you want decent life from the engine make sure you use a good quality, well known brand of engine oil and change it when it is too greatly discoloured from carbon which has escaped past the rings. This is use and load dependent, not on km's necessarily. GOOD oil seal the rings better , = more power and economy a bit, and the better ring sealing keeps the oil cleaner for longer. Junk oil promoted at Motor Houses isn't necessarily a good oil.
If engine well used, a possible retiming/check of the injector pump will see more power than at present, It does make a difference if not correct. Correct "even" valve clearances is a sensible thing to consider, ie, a tune up of engine.
AnswerID: 627097

Follow Up By: David Y5 - Wednesday, Aug 07, 2019 at 15:09

Wednesday, Aug 07, 2019 at 15:09

Thanks - I've added valve clearances and injector pump check to the list!

I've been using Mobil Delvac oil and replacing the oil and filter every 5000km. My driving mainly consists of a half-hour commute to and from work 3 to 4 times a week and perhaps 6 to 8 short trips a week where the engine doesn't quite reach operating temperature (~10 minute trips)... I also do a couple of 150km trips once every couple of months or so. I never end up towing a trailer as the tray fits everything I need.

It's only been ~800km since the last oil/filter change and the oil's looking pretty black already (still somewhat brown, though). I've attached a photo of the oil on the dip-stick. Is this normal or do you think it's already too discoloured? I was under the impression that diesel oil turns dark fairly quickly. Probably doesn't help that I'm partially colour-blind!


FollowupID: 901080

Follow Up By: RMD - Wednesday, Aug 07, 2019 at 16:57

Wednesday, Aug 07, 2019 at 16:57
Mobil Delvac MX is quite ok and your engine isn't known for being a clean engine, so the oil does discolour fairly quickly. That oil on the stick look normal to me. However, later, darkened oil does not mean it is due for a change and unless it becomes really sooty, staining black at 5000km you may not have to change it then. The idea of the oil is to keep the sooty crap "in Suspension" so it is drained out and doesn't cause a coat of crap buildup in the internals. Mobil Delvac is a high detergent, ie, engine cleaning oil and if changed regularly as you do, the engine won't suffer a carbon deposit problem. Cheaper oils are not as good at keeping internals clean. When I began my apprenticeship I was told the whole operation ran on Mobil oils in everything, that being one of the reasons it was used.
FollowupID: 901082

Follow Up By: David Y5 - Wednesday, Aug 07, 2019 at 17:22

Wednesday, Aug 07, 2019 at 17:22
Hey, thanks a lot! That's a wealth of information and very much appreciated. Will keep an eye out for sooty build-up.

FollowupID: 901084

Reply By: tim_c - Friday, Aug 09, 2019 at 10:28

Friday, Aug 09, 2019 at 10:28
Regarding rev-range to operate your car, listen to the car and feel how it is responding, as this will give you the most important feedback to whether you're driving it as intended or not. I'd have thought an older-tech diesel should be able to pull pretty well just above idle, unless you're really sticking the boot in.

If the car is not responding by accelerating when required, this indicates you are outside the useful rev-range. If revs are too low, the car will start to grumble/rumble and/or shudder and you won't feel the engine pulling - downshift. If revs are too high, you won't feel it pulling (particularly with an older tech diesel engine - you'll probably feel it pulling as you accelerate up until a particular engine speed and going beyond this you'll feel the power drop off and it will feel like all it's doing is making noise).

Over time, as you listen to the car and feel how it responds in different situations, you'll get to know what works and what doesn't, and this will be far more useful than watching your tacho' and memorising gear-shift positions.

And don't labour (ie. heavy acceleration, powering up a big hill, etc.) in fifth gear with is only an overdrive (ie. smaller gears, mounted off to the side of the main 'straight-through' gears, and therefore not as strong). I've heard quite a few people bragging about how their diesel car can pull up almost any hill in fifth gear, and only the next sentence they're telling you that fifth gear is noisy... (they've probably over-loaded the bearings which are now 'whining' in protest!).
AnswerID: 627126

Follow Up By: David Y5 - Friday, Aug 09, 2019 at 11:06

Friday, Aug 09, 2019 at 11:06
Hey Tim, thanks for detailing the practical side of things. I have a guilty habit of looking at the tacho too often... Definitely need to develop that feel!
FollowupID: 901108

Reply By: Batt's - Friday, Aug 09, 2019 at 10:28

Friday, Aug 09, 2019 at 10:28
So do these hiluxes have gear box issues are they to light for the vehicle ? I've has several diesel over the yrs and never had issues from loading up the box and letting the torque do it's job that's how you drive a diesel and you change gears less than a petrol but yes don't get to the point where your labouring the engine. When your towing then you use the revs as well as torque to keep it rolling you can find the sweet spot and don't ever be afraid to rev a diesel up to the red line when needed even if you have to hold it there climbing hills or sand driving etc they love it don't let any one tell you it is no good for them.
AnswerID: 627127

Follow Up By: David Y5 - Friday, Aug 09, 2019 at 11:12

Friday, Aug 09, 2019 at 11:12
Hi Batt, not that I know of. Generally spoken of as quite reliable. Never been up to the red-line; I don't think I've gone much over 3500... Thanks for inspiring confidence, though!
FollowupID: 901109

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