07 v6 petrol D40 stuttering under load, rough idle.

[Dan07D40]

Hi All,

Bought a 2007 v6 (petrol) D40 about a week ago with full service history and 300,000k as it was originally a company vehicle for its first five years. Owner had it sit in yard for one year as he was working fifo work and didnt need the vehicle. Upon test drive it was stuttering and running rough but suspected plugs and service was needed.

Once home I have changed plugs and changed oil as it was noticably low and smelt burnt. I left it at that for the time being to have a test fire and see if the miss had cleared up but no luck was still running very rough so shut it down. Have since pulled plugs again and noticed 3 of them had greying on the ceramic tips, I re assembled and started once more and opened radiator to look and noticed quite a large amount of bubbles (enough to cause overflow) so gave it a rev and as expected it rocketed out the coolant hard enough to hit the bonnet.

So I suspect head is blown and proceeded with a compression test, pulled all plugs out and fired roughly 5-6 times each cylinder and resulted in 170-180psi per cylinder. 2 cylinders both in line had a small compression seepage of 5-10 psi, old plugs were very worn and had a slight oranging to the tips which suggested to me coolant/water in the cylinder.

Now for some questions I right in thinking this has to be head gasket of head crack? could the psi drop be just seepage past the rings as its done 300,000k or does it indicate head? when first test driven it only ran rough under load and idled fine but is now idling rough and unsure exactly why. Should i go straight for the heads and pull them for inspection or should i first try injector filters etc? what else may be causing my rough idle and lack of guts under load? almost seems like its miss firing maybe?

Any help would be greatly appreciated as I do not have the money for a mechanic to diagnose. Thanks, Dan.

 

[Old.Tony]

Sorry to hear about the problems, head issues are always a worry.

The first thing to do with the compression test is to add a little oil to the cylinders with the pressure loss and see if there's still a rapid decline in pressure. If the pressure reduces more slowly (or not at all), it's more likely piston rings at fault.

However, given the placement of the loss, I'd hazard a guess at the head gasket between those two cylinders (or a crack there) allowing a loss of combustion gas into the water jacket.

There are four ways to repair this.

New head. Might not be necessary especially if it's just a head gasket (best scenario). Disassembly is required for diagnosis. It is the best, most reliable solution and also the most expensive.

Second hand head. Obviously some risk here of receiving a damaged head which may not be visible on inspection (eg a slight warp). Again, disassembly will be required.

Repair. Although it's not often done, I've spoken to people who have had the cracks in their engine heads welded, the faces re-machined and the heads worked perfectly. This may be more expensive than a second hand head but you know it'll be right. I don't know - I have not ever heard of - anyone who does this for the Navara.

Silicate in a bottle. This is amazingly cheap in comparison, sold almost everywhere (SCA/Autobarn/Repco etc and lots of service stations). It's basically like a glass in a liquid. You empty the radiator, flush it with fresh water several times to remove all traces of coolant. You then add this stuff, fill the radiator with water, run the engine and watch as the problems go away (read the directions, of course, for how long to do it). The fix is supposed to be temporary but I've spoken to people who have done this and the engine has lasted for years.

Hope that helps.