YD25 fuel economy, head gasket...where to start?

Hello,

I bought an '07 R51 Pathfinder, spanish built, YD25 auto early last year with circa 185k. I've driven and worked on older cars and bikes for years but this is my first diesel and actually first engine with an ECU. So a bit to learn about.

Originally I planned to post in here about the "journey" I have been on for a few months (for which this forum was insightful) trying to resolve what has been shocking fuel economy. We typically get around 17+L/100km around town and highway driving on roadtrips the very best we've had is 15.6L. Shocking. That is after I have:
- removed DPF
- blanked EGR cooler at exhaust end
- removed "jet" and blanked EGR valve at inlet end
- stage 1 remapped ECU
- full carbon clean incl MAF sensor
- replaced all vac lines to/from turbo (excl the short line from pump)
- multiple ECU resets doing the pedal dance

(has a roofrack but standard size tyres)

I was in the process of investigating boost and the BCS (which seems to be fine) when....the head gasket seems to have failed. Combustion gases in the coolant. Reservoir tank periodically pressuring and overflowing but coolant not being drawn back into the radiator. Couple of pics attached.

Radiator cap only a few months old so don't think that's the culprit. Water pump was recently replaced too. Likewise the reservoir bottle.

I've pulled a few heads off in my time but never done a diesel and don't really have the space to do it where I am living right now. Took it to a mechanic and was quoted $5k-$6k to do the head gasket and replace the timing chain. Pulling my hair out a bit now. I've had a bunch of people tell me to just run a copper sealant through and flog it off but I would never do that to someone else. Its either fix it or sell it as is (where presumably I would get nothing).

So...I'm not entirely sure what I am asking. I guess I would be keen to get some opinions from other more experienced owners familiar with this YD25 engine. Does $5k-$6k seem about par? I asked another mechanic who was recommended to me as a Nissan 4x4 expert and was given a similar quote (and 6 week wait). How many kms are these engines typically good for...are we throwing more good money after bad with nearly 200k on the clock? My wife and I primarily want to use it for camping, road trips and basic driving around town. Not a work truck and rarely towing.

The other thing in the back of my mind is spending $5k-$6k and still ending up with a vehicle which gets worse fuel economy than my 1975 Triumph's naturally aspirated 2.5L.

Sorry so much background detail. Any assistance or advice gratefully received. We're a bit stumped to be honest.

Welcome aboard.

If it's the head gasket, you could always slip in a bottle of Chem-Weld or similar. It's not the best solution though - obviously, changing the head gasket is the way to go.

This isn't a job to be taken lightly. You need to replace the head bolts (Nissan's workshop manual says to). Intake and exhaust manifold gaskets too. You'll probably unmount the turbocharger, consider putting a kit through it too.

Timing chains are a different kettle of fish. Their condition may depend greatly on the service history and driving history of the car. In my own car, my head cracked at 320,000km (we don't know why). I was at Bathurst for the races and just took my car to one of the local mechanics who had time to see me (Inwood Motors) and they diagnosed a cracked head - then did a fantastic job replacing it (I provided the replacement head). My car now has almost 370,000km on it and purrs like it did before. But those timing chains - the mechanic called me and asked me how long ago I'd had the engine rebuilt, because the timing chains and guides looked in perfect condition. He was stunned when I told him that he was the first person to see those chains since the engine was assembled at the factory. He recommended to leave the original chains and guides in place. I agreed (I did ask him to replace the thermostat and the water pump, the latter was in perfect condition).

Regular servicing and moderate driving have been the key. I use an Android app called "Torque" to monitor several aspects of the engine but pay most attention to the coolant temps, with an alarm set at 105C. I try not to let it go past that.

Inspect yours by all means, but if your car has been treated well, you might get away without touching the chains.

Oh, fuel economy ... will suck in the auto if it's not driven in the sweet spot. The torque converter's stall point should be around 2700rpm, so accelerating is best done around that point (because you lose less RPM to the fluid drive). On roads with 70km/h or more speed limits, make sure the car's in Drive, ease off the throttle as you reach 70km/h and allow the torque converter clutch (TCC) to engage. You'll notice it as you'll still have drive but the engine revs will drop, light throttle application will see the car wind up to speed with the revs rising exactly with vehicle speed.

If the TCC has failed (happens, it can wear out), it won't engage or it will vibrate as it's engaging (and may not 'stick'). This requires the services of an automatic transmission specialist - and not a backyard operation, take it to a larger mob and have them replace the entire torque converter (I had mine rebuilt - big mistake).

Consider a torque converter with a lower stall speed - Wholesale Automatics in Victoria make one that stalls around 2400rpm (I think). This will "bite" earlier, reducing lost RPM and reducing fuel consumption.

Finally: how are you calculating fuel usage? I do mine like this:

(fuel used) divided by (hundreds of km travelled)

Example (actual figures I've had): 1104.2km travelled (= 11.042 hundreds), fuel used 135.68L (I have a 150L tank).

135.68 / 11.042 = 12.287LPHK

Old.Tony said:

Welcome aboard.

If it's the head gasket, you could always slip in a bottle of Chem-Weld or similar. It's not the best solution though - obviously, changing the head gasket is the way to go.

This isn't a job to be taken lightly. You need to replace the head bolts (Nissan's workshop manual says to). Intake and exhaust manifold gaskets too. You'll probably unmount the turbocharger, consider putting a kit through it too.

Timing chains are a different kettle of fish. Their condition may depend greatly on the service history and driving history of the car. In my own car, my head cracked at 320,000km (we don't know why). I was at Bathurst for the races and just took my car to one of the local mechanics who had time to see me (Inwood Motors) and they diagnosed a cracked head - then did a fantastic job replacing it (I provided the replacement head). My car now has almost 370,000km on it and purrs like it did before. But those timing chains - the mechanic called me and asked me how long ago I'd had the engine rebuilt, because the timing chains and guides looked in perfect condition. He was stunned when I told him that he was the first person to see those chains since the engine was assembled at the factory. He recommended to leave the original chains and guides in place. I agreed (I did ask him to replace the thermostat and the water pump, the latter was in perfect condition).

Regular servicing and moderate driving have been the key. I use an Android app called "Torque" to monitor several aspects of the engine but pay most attention to the coolant temps, with an alarm set at 105C. I try not to let it go past that.

Inspect yours by all means, but if your car has been treated well, you might get away without touching the chains.

Click to expand...

Thanks so much Tony. Very encouraging to hear yours is running great with 370k on the clock. Are others enjoying similar longevity from their YD25?

Re the timing chain, having only owned it < 1 year there's a whole bunch of unknowns as far as the service history goes and how it was driven by previous owner(s). I know it had a consistent service history with Nissan dealers from 73k to 113k but no records after that until 184k. Not to say there wasn't, I just cannot see it.

Replacing the timing chain at the same time was recommended to me by the mechanic I think based solely on kms, but if I hear you correctly you recommend it be inspected but don't commit to a renewal if everything looks to be in good shape. Yes?

Re the Torque app, yep I downloaded that one a while ago (pretty sure after reading one of your posts) so I could check the boost. Never considered having it running all the time and was not aware of the alarm function. I will check that out.

Old.Tony said:

Oh, fuel economy ... will suck in the auto if it's not driven in the sweet spot. The torque converter's stall point should be around 2700rpm, so accelerating is best done around that point (because you lose less RPM to the fluid drive). On roads with 70km/h or more speed limits, make sure the car's in Drive, ease off the throttle as you reach 70km/h and allow the torque converter clutch (TCC) to engage. You'll notice it as you'll still have drive but the engine revs will drop, light throttle application will see the car wind up to speed with the revs rising exactly with vehicle speed.

If the TCC has failed (happens, it can wear out), it won't engage or it will vibrate as it's engaging (and may not 'stick'). This requires the services of an automatic transmission specialist - and not a backyard operation, take it to a larger mob and have them replace the entire torque converter (I had mine rebuilt - big mistake).

Consider a torque converter with a lower stall speed - Wholesale Automatics in Victoria make one that stalls around 2400rpm (I think). This will "bite" earlier, reducing lost RPM and reducing fuel consumption.

Finally: how are you calculating fuel usage? I do mine like this:

(fuel used) divided by (hundreds of km travelled)

Example (actual figures I've had): 1104.2km travelled (= 11.042 hundreds), fuel used 135.68L (I have a 150L tank).

135.68 / 11.042 = 12.287LPHK

Click to expand...

I confess the above numbers are taken primarily taken from the console display, including after an ECU reset. But even calculating as you suggest based off the fuel bowser and trip meter (which I habitually reset every tank), the best we've ever got was still high 14s after highway driving all day. We've certainly never got over 500km from a tank.

Pretty disappointing because one of the big appeals of this engine before we bought it was the encouraging economy, but to date that has not been our experience. I dream of the figure you quoted!

I should add, in addition to the above, we have also tried filling up with better quality diesel (mostly BP and Shell) but no discernable change. For what it's worth I have also installed a snorkel, which I know improved the economy in my old man's 80 series, but no change for us there either.

Once it's back on the road I will definitely check out the TCC and the rev range you suggest. Thanks for that. To be honest we drive it pretty gently (or at least I do...might have to have a yarn to the wife ) and have not noticed any issues generally with the trans to suggest TCC has failed. Question though: if part of the issue is accelerating at a less than ideal time, wouldn't that primarily affect "around town" fuel economy and highway driving would be less affected?

The mechanic did also mention to me that they inspect (and possibly service?) the injectors while removed, so I am cautiously harbouring a fleeting hope that this might also yield some improvement to my thirsty machine.

I'm always concerned when I hear about remaps.
Most remapping companies just upload a generic remap they have bought. These generic maps simply push more fuel into the injectors. As they are not done on a rolling road, the end result is more power at the expense of economy.
Not unexpectedly, throwing a load of extra fuel into a 15 year old engine isn't going to please the head gasket.

landmannnn said:

I'm always concerned when I hear about remaps.
Most remapping companies just upload a generic remap they have bought. These generic maps simply push more fuel into the injectors. As they are not done on a rolling road, the end result is more power at the expense of economy.
Not unexpectedly, throwing a load of extra fuel into a 15 year old engine isn't going to please the head gasket.

Click to expand...

Hi LM, thanks for your input.

The remap was primarily to code out the DPF and EGR from the ECU. Unfortunately the economy was lousy beforehand too.

The bloke who did the remap did suggest it might use more fuel around town but would be better on the highway. He also said this could be mitigated with a an ECU reset before and after long trips where the ECU adapts to driving style (which I understand this one does). I did try that for a bit but confess did not notice any material change. Or at least not in the console reading.

As for the head gasket, when I bought the car the existing EGR cooler proved to be knackered with some sneaky leaking so I wonder if it was driven hot before I got it. Perhaps they even did the gasket then and then quick-fixed it with a sealant before on-selling. Just a theory.

A second hypothesis: the bloke who came around to do the carbon clean (immediately after the water pump and reservoir were replaced) as part of the service tried to trigger a DPF regen (even though I told him twice it did not have one) then rang me at work because coolant was overflowing from the reservoir tank and he did not know what to do. Impossible to prove, but I also wonder whether he ran it unnecessarily hot.

Either way, I am presently stuck with a buggered head gasket and a fuel economy issue to still resolve on the other side.

Personally I would get just the head gasket done. No real benefit in getting the timing chains done at the same time as one job is the top of the engine and the other the front.

They most common reasons for fuel consumption being poor are a dirty MAF or a leaky injector. There are specialists around who will properly clean injectors and check the spray pattern, it might be a good idea to ask your garage to get the injectors out and send them off.

By the way, fuel pump learning doesn't learn driving style. What it does is make small adjustments to the fuel delivery map depending on what it sees from the oxygen sensor in the exhaust.

^ True, but the upper chain has to come off to get the head off. It's worth inspecting at the very least. If the tensioners still have a lot of travel left, the chains wouldn't have stretched much so they're probably in good nick. If the tensioners haven't been eaten away a lot, same deal. They can suffer through lack of oil changes by gumming up, not tensioning the chain properly and the chain starts snagging sprocket teeth, so have a really close look at the sprockets too. If they all look good, it's probably safe to leave 'em, but note that the lower timing chain is a single row chain not a duplex and it drives the pump, so while it's apart you might consider changing them all anyway. I didn't see the need, and with 50,000km or so on board since the work was done and it still purrs, I think I made the right choice.

High km is entirely possible. We anticipate having to replace unis, wheel bearings, vac hoses, maybe a radiator, certainly a few sets of tyres (only getting about 70,000km to a set) before we are forced to retire this girl - we're hoping it'll reach 700,000 at least before it needs any more major surgery.

This is tough one. What a bummer!
If I might offer a single point of view.....

I think you have 2 main choices, with a sub-decision included:

1. If you've lost faith in the car & starting thinking about a replacement, then rectify the head gasket issue and sell the car.
Move on to something with less kms & a better history. This way you'll be down the cost of the h/g work (see sub-decision below) but will recoup a decent sale price. Leave the economy issue for the next owner.

2. If you still like the car and it's in good nick (what's the interior like? How scratched is the paint? Are the shocks stuffed? Does the stereo & A/C work etc etc)
Then I always say "you can't be half-pregnant".
I'd go full rebuild - h/g, timing chains, injectors, T/C overhaul etc etc. Or buy an exchange engine from a reconditioner?
And then keep the car for longer knowing you have a nice fresh engine. You'd also be benefitting somewhat from the money you've already spent on repairs & troubleshooting. Take the financial pain now, but restore a big chunk of faith in the vehicle.
I also think that the fuel economy issue would be solved during this process.

The sub-decision? For option #1, it's whether you tackle the h/g job yourself and save much coin....or book it in to the local workshop.
It sounds like you could do it yourself....if a mate can lend you some garage time & space?

Okay an update on this one.

Shortly after the above post I bit the bullet and took it to the local mechanic to do the head gasket and, subject to an inspection, the timing chain if it appeared warranted. He didn't have space until mid-March and it has been with him ever since (yep...approaching 2 months). I won't bother documenting my frustrations with timing and lack of communication here...

The abridged version is he has not pulled the head off. He apparently did some tests and is not confident the bottom of the engine is much chop and for that reason has been looking around for a replacement engine (which he is struggling to find). What the test is exactly I am not sure as it has not been clear, but I believe he said he detected an increase in compression once he ran the motor warm which he said can indicate pockets of (something...heat, pressure?) in the block which one cannot isolate without pulling it down. Wasn't clear at all to me. I tried to understand what he was saying but the call was brief, he was speaking fast and more or less concluded saying he's not a fan of these YD25 engines and reiterated his prior belief I should have just traded it when I knew there was a head gasket problem. Consequently he does not want to do the head gasket and possibly replace the head only for other terminal issues to arise later and me come back to him.

I've been racking my brain and I am sure he said "compression" and not "oil pressure". In which case I have no idea what he is talking about as I expected compression would naturally increase somewhat as the engine warmed. Anyone got a clue what he might be talking about?

So for the last 6+ weeks he has apparently been putting the call out "on the hotline" for a replacement YD25 and to date he has been underwhelmed with the results. He said he does not want to charge me circa $12k to put in a 200k+ reconditioned engine but also does not want to send mine away to be rebuilt because there is only one bloke he trusts on the Coast (Rob Abbott) and he has cancer at the moment so cannot take the job.

When we spoke last Wed he was going to try one other mob he knows up on the Sunny Coast then give me an update last Friday but surprise surprise we are at Wednesday again and still no news. In the meantime I drive past my Pathfinder multiple times a week parked up out on the street half a block up from his workshop, never moving and apparently no closer to being repaired.

I am thinking I will just pick it up, pay him whatever I owe him and take it somewhere else. I sure am not interested in forking out $12k to replace the engine, especially when I am still so unsure as to what exactly the problem is and how reliably it was diagnosed.

I have such mixed feelings. Notwithstanding the shocking communication/updates I do really feel this guy knows his stuff and I appreciate the fact he is trying to foresee future problems and so save me money in the long run. But I also have a sense he just despises this YD25 motor and would rather not get too involved in it. I think he thinks I'm silly wanting to fix it.

From experience as these motors get up on the ks you will be constantly chasing your arse and emptying your wallet, a lot of people think they know the engines but they don't, I have had mine from brand new and the cars are plagued with problems, my problem now is they are worth nothing so you just have to keep fixing stuff as it goes wrong until its time for the wreckers, remember these cars were manufactured when Carlos Ghosn was the main man and had done so much shonky deals and cut corners on parts, labour etc.. to ensure he maintained a guaranteed margin of 8% that he promised to the board of Nissan on all vehicles, and of course so he could still fleece the company.

Appreciate your candour TCN, tho I am a tad confused too. Didn't I see you say elsewhere you've driven your rig 402,000kms since brand new and the TC bearing letting go is the "first major thing to go wrong...so can’t complain"? Not your view anymore?

You are correct however, I've been lucky up to now I was more referring to the cars in general are worth nothing now compared to other 4wds in their era and every where i have taken mine the (honest) mechanics say don't want to even start to try and fix for you, as the engines are plagued with problems and others try and guess at your expense, so if you are having these issues with less than 200k on the clock i would be concerned, it was one honest mechanic here in Perth that said to me about the issue of cost cutting in production, single chains, thin paint, snapped chassis, relocation of production from Spain to Thailand.. that i did the research on Renaults and Nissan partnership woes

Hello
Referring to your fuel economy , mine is 2012 auto. On highway @110 it does high 9s , 8s a@100 Towing my 2T camper at 113 it averages 14.3/14.7 , I use GPS klm , not what the dash says , the fuel consumption on dash says it's heaps better.
Always has, it has 185k, only thing that died was the turbo, ccasnt really blame nissan, Garrett made it.
My old work vehicle was a 2013 d40 Thai, overheated and died, I think was about $5500 for second hand engine plus labour . But that vehicle was trouble from day dot, chalk and cheese between that one that and my personal one.