Suggestion for improving G.U. Patrol 4.2 turbo diesel fuel economy

Submitted: Saturday, May 06, 2006 at 00:42
ThreadID: 33596 Views:38437 Replies:11 FollowUps:3
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Hi all,
I have a 2001 4.2 turbo diesel patrol wagon and I'm looking for ideas to improve its fuel economy.Currently I get approx 650kms for both tanks & and it doesent seem to matter how I drive as the economy doesnt seem to change by more than 50ks. Ive exhausted all ideas from the local Nissan dealer.
Ive been told that I will have to install a 3" exhaust system & an after market intercooler to achieve a 20% increase in economy. This I will gladly do if the gains are to be had.
Have any other members done this ,and if so did you achieve any economy gains?
Regards Paul Reilly
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Reply By: choco - Saturday, May 06, 2006 at 01:38

Saturday, May 06, 2006 at 01:38
Dunno about 20% increase in economy Paul but I have a 1999 GU TD42 with a 3" dump pipe and exhaust system on. A recent trip from Melb to Albury sitting on 110Klms returned 11.8 ltrs per 100k's or 8.47ks per ltr. I was happy with that. Dyno figures after the pipe was fitted and some turbo and fuel pump tweaks showed a 17kw gain at the back wheels. Thats not bad considering the age and technology of a TD42 deisel I guess. Save yourself a few quid and skip the intercooler....the pipe and the other simple mods is a good place to start.

AnswerID: 171079

Reply By: Member - John - Saturday, May 06, 2006 at 02:08

Saturday, May 06, 2006 at 02:08
Paul, I have had a 3" dump pipe, exhaust, a modified MTQ turbo fitted and fuel pump timing mods done, went from 72 kw to 120 kw at rear wheels. 2000 GU ute. If, big IF, I haven't used the extra HP I would have made good fuel savings, but it is so easy to drive that I find I don't save fuel, I use the extra HP to beat traffic etc instead of just keeping up. I have added an intercooler, top mount, a further increase in HP, how much I don't know since I haven't had it on a dyno, but above 75-80 K's a much crisper response, and I am saving fuel, not much but saving it. It can be done, costs a fair bit, but yes you can save juice. Bet you won't though, if you get the mods done, you will drive it harder and negate any fuel savings....

Maybe fit a Fitch and Hiclones, lol
John and Jan

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AnswerID: 171080

Reply By: Trevor R (QLD) - Saturday, May 06, 2006 at 04:57

Saturday, May 06, 2006 at 04:57

I'm with John, have also had the MTQ upgrade put a front mount intercooler ect ect.
It's just too easy to drive like you want to drive when you have this work done and poor fuel economy is the result. If you drive like grandma and have this work done you will save fuel but I think it would take a long time to recoup the money spent on getting this "better" fuel economy.

Cheers Trevor.
AnswerID: 171083

Reply By: Member - Ian H (NSW) - Saturday, May 06, 2006 at 08:14

Saturday, May 06, 2006 at 08:14
I have and 80 series and fitted turbo to the diesel 12 months ago. The fuel economy hasn't changed but the output went from 96 to 136 kw. You have to remember we are hauling 3 tonnes around no matter what engine you have. It is a matter of energy consumed to do the work involved.
AnswerID: 171096

Reply By: Michael ( Moss Vale NSW) - Saturday, May 06, 2006 at 08:32

Saturday, May 06, 2006 at 08:32
HI ,My 2004 4.2 tdi gets 620 from the main tank and 230 from the aux consistantly highway running and drops to about 520 and 180 towing my offroad trailer. My old 1999 4.2td gets 700 and 200.. Maybe spend the money on a good tune from one of the reputable diesel guys. thats really low.. Michael
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AnswerID: 171101

Reply By: Member - 'Lucy' - Saturday, May 06, 2006 at 10:30

Saturday, May 06, 2006 at 10:30
Paul & others

Sometime ago I put a DTS (Now MTQ) turbo on a 1HZ.

After doing so I had a loooooong chat with a guy (cant remeber his name) at MTQ re Dump pipe, Exhaust & muffler peak efficiency specs and this was his no ifs/buts reply.

(1) The exhaust pipe MUST equal the dump pipe in diameter. Can be greater, however doesn't do anything other than cost extra to supply and fit.

(2) The exhaust pipe has be the same diameter from dump pipe to final outlet. ie use of mandrel bends mandatory or if you have the $'s a custom 'sand' formed one piece jobby.

(3) The Exhaust/resonator has to be a straight through affair. Noise is not issue as the turbo kills/negates 90% of it.

He further stated that MTQ supplies dump pipes to match OEM specs for marketing purposes only.

He explained that because Nissan supply a 3in pipe, MTQ matches that even though their turbo outlet( depending on kit model) may be 2.5in. It apparently doesn't enhance anything other than everyone after the first point of sales 'mindset', that 3in is better than 2.5in (on turbo setups that is)

Having said that he was quick to point out that if it comes with a 3in Dump pipe then you must continue with 3in all the way to the end.

I then asked him about Intercoolers.

He stated that in the cooler climates (below the Murray as a rough guide) you would see little effect for the dollars spent in relation to 'normal' 4wd operation.

Above that imaginery line the inter cooler starts to have a noticeable effect due to increase in ambient heat conditions, where once you enter the tropics they are an effective item.

Q. why then do they sell these vehicles with intercoolers below the Murray line.

A. because they leave the factory with them fitted with no knowledge where they will end up, unless for a specific individual order.


I then had a 2.5in mandrel bend exhaust fitted with a straight through resonator.


(1) Turbo lag/spool-up virtually eliminated

(2) Quieter than the OEM muffler

(3) Drive like Grandma increases fuel consumption

(4) Drive like you need to and it goes like C H I T off a shovel , however the fuel guage reacts accordingly.

Hope this gives you some insight.
AnswerID: 171112

Reply By: Member - Roachie (SA) - Saturday, May 06, 2006 at 14:56

Saturday, May 06, 2006 at 14:56
G'day Paul,

I've got a 2000 model GU and I've spent a lot of $$$$$ on it trying to get maximum power and cooling.....haven't been too concerned about economy up until recently. The other blokes have concentrated their responses on engine mods etc. This is all okay, but there are a couple of more basic things to also be thrown into the mix.

1. If you have a roof rack or bars, this will sap your economy by about 10%. I fitted a ARB heavy, full length roof rack when I bought the vehicle new in 2000 and it hasn't been off ever since....This is because of the permanent gear I have up there like UHF aerial, air horns, rearward-facing lights, shovel etc.

2. Tyre pressures; I used to run my tyres on bitumen at 32psi. I now run 42psi. This will assist lower the rolling resistence of your truck on the black top and will assist with economy.

3. Tyre type; I use Goodyear MTRs which are boardering on being a mud-terrain tyre. I know this decreases my economy, but it's one of those trade-offs I can live with. I go off road too often to bother with farting around with a dedicated set of off road rubber and another set of highway tyres. However, the latter type will save you some fuel.

4. Weight; if you wanna save money on fuel, put your truck on a crash diet (sorry, poor choice of words...."crash"......when talking about motor vehicle). I've given up on this one except that I do take the heavy crate of recovery gear out of my truck except when I go on a trip. Also, I have a dual spare wheel set-up with heavy rear bar (no plastic at the front or back of my rig!!! ;-)). Even after trying to get rid of any non-used gear, mine still weighs over 3T before I load up for a trip!!

Now, as far as the under bonnet mods are concerned.........I've had a 3" mandrel bent system for a few years now with a larger dump pipe. I don't believe the fitment of that system improved my economy. More recently (October 2005), I chucked the standard old Nissan turbo (which apparently is the same one that Nissan has on it's 3.3L MQ Patrol back in the 1980's, so you will appreciate that it probably is a bit under-sized for the job at hand.......but that's the sort of thing Nissan does.....don't forget the more recent 4.2TDI uses the same intercooler as the 2.8L Patrol had!!!.....they don't like to see anything go to waste over there at Nissan!!!!!). The turbo was replaced by a Denco kit which utilises a Schwitzer turbo. I was fortunate enough to have had mine done by Berri Diesel Service, SA and the blokes there were (unlike most workshops) happy enough for me to hang around for the day and watch the work be done. As such I saw the new and old turbos side-by-side on the work, was there some difference in the size of those 2 hair-dryers or what!!!!!!????? They cranked my boost up from 12psi (factory is around 8 or 9 psi) to 15psi.

I've achieved more power and quicker spooling of the snail, but haven't changed my economy at all. It's worth noting that the 3" exhaust system which i fitted in 2003 is still on the vehicle and it utilises a straight-through Lukey hot-dog muffler and no other mongrel things like resonators etc. It is no louder than a standard 4.2TD, but does have a different "note".

In short, I don't think there are any sure-fire fuel-saving methods for the 4.2TD, other than drive like granny. You own a "truck" and need to expect it to drink like one (unfortunately). The alternative would be to sell it and get a that'll save you some money (on fuel).....but don't spend the savings on beer, cos you're gunna have to save up for a new motor after 100,000klm or so!!!!!! (Sorry to all those satisfied 3L owners;-))))


AnswerID: 171142

Follow Up By: Member - JohnR (Vic)&Moses - Sunday, May 07, 2006 at 08:18

Sunday, May 07, 2006 at 08:18
G'day Bill, I was pleasantly surprised to get 1200 kms tank to tank the other day in Moses including low ratio work over the Pyrenees with the Riverlanders. This was the first time I had really watched it after fitting the 3" mandrel bent system.

I know I would have been beating grannie a few times at the ligfhts as I have been watching the Stop sign into Timboon to the 80kph and see what I can get to. (Just as well as there havent been any hairdryers out taking note) Even with that it has been better than 14.6 litres/100km. Regulars will remember Moses isn't a lightweight, so I was pleased. Should be able to coach him to do better some time.

NAB girls and boys taking me to the footy early August mate. Pity it's a Saints/Weagles match.
FollowupID: 426716

Follow Up By: Member - Roachie (SA) - Sunday, May 07, 2006 at 12:58

Sunday, May 07, 2006 at 12:58
G'day John,

That's not too bad (ie: 14.6L/100) and would be about equal to the best figures I've ever recorded (longish trip without trailer.......pretty rare for me...hahaha).

However, to get 1200 tank to tank (and I just checked your rig profile info), may I ask what your capacity is? I seem to recall the cab chassis has 2 x 95 litre tanks? That is a bit more than my 145 + 34, but I reckon the most klicks I've ever had is about 1100klm from both tanks.......But then again, I know my speedo is out by around 7% (so when I say I've done 1100 klm, I know I've done more like 1177klm). However, that 1100 figure is rare..........I'm usually looking for a fill-up at around 800 to 900klm as the sub has been pumped and the main is showing a quarter (which really means it has got stuff all left in it afaik).

Cheers mate......I'll have to charge some extra fees to clients to make-up for the cost of sending you to the corporate box!!!!!! hahahaha

FollowupID: 426755

Follow Up By: Member - JohnR (Vic)&Moses - Sunday, May 07, 2006 at 17:27

Sunday, May 07, 2006 at 17:27
I thought you had spent the corporate box entitlements on the GU mods Bill. I am glad you are thoughtful enough to contribute enough to our night at the footy. One of your agribusiness competitors is taking me out to dinner interstate in July. They know how to entertain.

I have the standard tanks on the Coil Cab totalling 175 litres. A 95 l. main tank and the 80 l. subtank. I usually empty the subtank before the other gets too far down and fill it first to check the fuel bowser against it. 80 litres or less is good. Did get in excess of 85 in Mildura once at a discount outlet in the 80 litre tank. My speedometer is out by about 4% but the odometer is very good when I have checked against the GPS.
FollowupID: 426787

Reply By: warthog - Saturday, May 06, 2006 at 19:24

Saturday, May 06, 2006 at 19:24
I also have a td42t and have gone for mods to improve the power and asked for our local diesel specialist to tune for power which he has done. I am now considering going back and saying I don't care about power, can you tune it for economy. I understand you turn up the fuel setting to get more power in a diesel, does that mean you can wind it back and get better economy? Also has anyone done the injectors in their td42 and noticed much change in economy and power? Ours has 115k on it, maybe they need checking, doesn't seem to belch smoke though.
Paul, our economy is up and down, but it is better than yours. Last fill was 800k's for 110 ltr around town. Have a safari front mount intercooler, 3" mandrel exhaust and dump pipe and running 10.5 lbs boost and the injector pump timing has been advanced from the std setting. You should get better than 650 to a tank with just a tune I reckon
AnswerID: 171178

Reply By: Bob Y. - Qld - Sunday, May 07, 2006 at 10:56

Sunday, May 07, 2006 at 10:56

Have an 80 series tojo, multi-valve turbo, which has had a 3" mandrel exhaust fitted. Did notice a small increase, in economy, after fitting, but hadn't always taken accurate figures, to provide credible before & after figures.

However, when in Brisbane area, on holidays each year, we always get over 8kms/L, driving around that area. As we avoid peak hour areas(not always possible), manage to get acceptable economy.

Once on the highway, at 100-110 clicks, economy drops to back to 6 or 7 kms/L. Don't use a roof rack, and BFG AT's @32psi.

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Can't remember most of it.

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AnswerID: 171261

Reply By: Leroy - Sunday, May 07, 2006 at 22:40

Sunday, May 07, 2006 at 22:40
650km for both tanks seems like something is wrong. I 'd be off to a diesel specialist for a good dyno tune. I just filled up on my way home tonight and was towing a 4.8m boat and put in 111l for 780 km. That's a 3l but I would expect similar for a 4.2. I can't get below 12.5l/100 but have put it down to a lead foot and 285/75's.

AnswerID: 171441

Reply By: Flash - Monday, May 08, 2006 at 22:01

Monday, May 08, 2006 at 22:01
Think I'll stick with my GQ TD42 Wagon for a while yet.
Been away for the whole of April towing my 2.5tonne van and average for the whole trip (some 3,900 klicks) was 13.8litres/100klms. Probably 90+% of the time towing- just some short day trips without the van on the back.
DTS turbo, modified wastegate setup running 12psi boost and 3" exhaust.
...absolutely the best and most reliable vehicle I've ever owned by a country mile.
Good luck in your hunt for better economy.
I'd certainly be doing a turbo and exhaust upgrade in your position for starters. I have a mate who did that and it's a different vehicle now. Much better power AND economy.
AnswerID: 171628

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