Very small loss of coolant D40

I have a nagging problem with a loss of coolant.

I'm losing about 0.5 litre or less every 500 km or so.
the temp is fine at normal I just have to check the water bottle every now and then.

2 separate garages have carried out a pressure test and tell me the is no leak....but the loss continues.

There is no noticeable smoke, loss of power or any abnormality in running.
it has just had a service and there is no sign of water in the oil

On a couple of occasions, i have spotted a few drops of coolant on top of the main (larger) hose from the cylinder head - literally about 6 drops of coolant - I can't see anywhere it might come from.

the vehicle is in Thailand and is NOT fitted with a heater - it simply has a cold air-con unit.

Model - 2009 4x4 4dr with 150,000 km on the clock.

any ideas?????

Given the small volume being lost, this isn't going to be easily fixed in text!

The large hose coming from the engine at the top is the "hot" side. You'd think that a leak from there would be obvious.

Pressurising the radiator to 157kPa (23psi) and hunting for leaks is the first step. There are numerous places to look:

* EGR cooler (if EGR valve is fitted).
* turbocharger coolant lines
* Oil cooler (intake manifold side, near oil filter)
* Water pump (front of engine immediately behind the fan)
* Plugs on the side of the engine block's water jacket (the outer part of the block)
* Transmission fluid contamination if the car's an auto (I don't remember if yours is)

THanks for the list.

Mines a 6 speed manual......it also doesn't have a heater.

the EGR pipe doesn't seem to have any connection to the cooling system.

I've had THREE pressure tests on the system by TWO different workshops (Nissan and a local chap) - they both came back OK.
however I don't know what pressure they checked it at - I assumed they would know?

i'm going to tale the car to Nissan again of Friday for a couple of other things so I'll give them your list and see what they say......the one thing with Thailand is I won't get a huge bill for labour!

i was wondering if the drops of coolant (which may have come during inspection) could have been blow up from the water pump into the engine cover and then dripped down?

anyway, thanks for the help....I'll be back on on Friday evening depending on how I got on with my Nissan lot....

3 months on and the problem continues...

Well, i've run it for about 10,000 kilometres or more; there is no over heating, no smoke, no water in the oil, no oil in the coolant...in fact everything is fine.....apart from losing a small amount of coolant....about one litre to 300 km, but this is far from constant.......

One thing I've noticed is that it only loses coolant during what I'd call "urban cycle" - if I use the vehicle every day and commute about 20 to 30 km - stopping and starting - , then it loses coolant.

If I drive long distance, 600 km or more, the level hardly changes.

PS - can anyone draw me a diagram of the coolant system on a Navara? I'm particularly interested to see how the reservoir fits in - i.e. inlet/outlet pipes and what controls the level in the tank.

The reservoir (plastic bottle) isn't "controlled" as much as it is a guide to whether or not coolant has gone missing in the radiator. It's connected to the top of the radiator tank and the level inside is changed by the temperature of the coolant.

The flow diagram on p36 of the manual for the European model includes EGR and heater core circuit which you don't have. Flow for yours would follow this path:

Pump
-> cylinder block
-> cylinder head and (turbocharger plus oil cooler -> return pipe -> thermostat housing)
-> thermostat housing (when cold) OR
-> radiator (when hot)
-> thermostat

In European/Australian models the EGR and heater cores are fed from the cylinder head which then connects to the heater return pipe to the thermostat housing.

That oil cooler (yours should have one!) is on the side of the engine near the oil filter.

As for the difference urban/highway cycle - on the highway your engine should be sitting at a roughly constant 2,000rpm or a little over. When in the city, your engine might reach 3,000rpm or more - the pump will work harder, producing more pressure and flow - maybe this is what's causing the leak? A pressure is reached that is higher than the testing pressure?

Here's something to try that might help shed some light on it and it won't cost you anything except a few seconds. In the city, keep your RPM during acceleration as close to 2,000rpm as possible (maybe 2200 tops).

Thanks for the continued advice.....re "urban cycle" - I have done the opposite... That is driven it hard on the open road to see if the loss increased, but to no avail.
My work dictates where and how far I'll be driving...
For the next month my driving will include mostly motorway driving at 120 kphabout 130 km per day... So I'll use that to monitor the situation.
If I get into a town, I'll keep the rpm down.
Although I have to wonder if the engine was ever getting to full operating temp when I was just driving around town.

That's the other possibility - that it's only when the thermostat opens fully and the coolant expands from the heat. It's a liquid, so when it heats up it will be somewhat thinner - allowing it to pass through gaps that it otherwise wouldn't.

It still means you're looking at somewhere that the coolant flows to that is connected to either the intake manifold or the exhaust directly.

The turbocharger is cooled by the coolant - I wonder if you've got a leaky seal in the turbocharger that's causing the coolant to squeeze out past the turbine into the hot exhaust stream. You'd never notice it. If it leaked out after the engine stopped it would sit inside the exhaust until the engine heated it up, boiled it and passed it out the exhaust.

Have you tried replacing the radiator cap on the expiation tank. If so .
Try using some stop leak the one with copper in it.
I've been having the same problem with my D40 too.

yes first thing to replace would be the Radiator Cap.

A conclusion... Well I replaced the radiator cap... No luck.... I finally have fixed though, by replacing another part... The cylinder head.

It's a good news bad news thing... And the head has to be tested and serviced in the next 1000 km.

The gasket was fine
A valve guide was not. Apparently damage to an (exhaust?) Valve guide allowed coolant to leak in. One of the manifold ports was completely clean... No carbon deposits at all .

I got so fed up of my local Nissan dealer telling me there was nothing wrong that i finally got in touch with Nissan HQ, Bangkok. They refused to speak directly to me but sent someone to the Chonburi dealership and got the ball rolling. this after i left the vehicle there with instructions not to return it until the matter was sorted.

Once diagnosed...this took about half a day... there came the cost.......
As i had reported this problem nearly 6 months ago, my contention was, and still is, that Nissan are at least partially to blame for any compounding of the intial damage.
they resolutely refused to discuss this, but without consulting me have offered 15% on parts and 10% on labour.
As i need the vehicle for work, i've paid this but intend to follow up later. i've indicated this on the bill.


what was the cost? you may regard this as the good news part.....

Well initially nearly 50,000 baht (including 25,000 for the head) but following discount just over 40,000.
If you work that out in AU$ its from about $1900 to about $1500.

As yet I haven't run the car much - the next week will tell.
However there have been other issues..on picking up the vehicle i noticed that the ARB compressor had been mounted incorrectly and the relay damaged.
I had also received a text before picking up the vehicle asking me if I used gasohol 91 or 95...one would have thought that after changing a cylinder head one might have noticed the vehicle was DIESEL!!!!!

It remains to be seen what other bits and bobs have been left undone....bear in mind all this was done 2 weeks after I'd send the truck in for a full service...actully I hadn't asked for this, I'd asked they check for the coolant leak......

PS - I have some photos which i will post later maybe........

The resolution is great, the means of finding it, not so great. It's a weird one - why would one exhaust valve guide go? There must have been a crack through from the water coolant path to the guide. Could the head bolts have been tensioned incorrectly?

Did they give you any indication of what might have been the cause?

no, ....... i think it is unlikely i will ever get an explanation as it would implicate Nissan somewhere down thhe line....
They did ask me if I wanted the cylinder head, but frankly this is normal in Thailand...you end up with a heap of old parts that the garage doesn't then have to bother disposing of. and I refused.

if you have any ideas on how this could happen,
i'd be interested.....i get the feeling that
nissan hq are aware that this is their fault, but getting thhem to admit this in
thailand is an up hill job.

i have to say that it seems to me that EVERY TIME I asked them, to check the engine, they actually didn't bother...they relied solely on doing a pressure test. If they had removed the black plastic cover over the top of the engine they may well have seen signs of what was going on right from the start....i have no idea about how much damage could have been avoided, but it is quite common for this apparently absurd behaviour by service teams in Thailand.

PS - Did I tell you about the time they failed to change a UJ on the prop shaft?
They told me "nothing wrong" but the noise continued....eventually the problem was solved when I pointed out the vehicle was 4WD and it was the FRONT prop I was concerned about.......

PPS - I got the vehicle when it was 18 months old and still under warranty...and spent an afternoon driving around with a team of 'experts' listening to a 'click' from the engine that was eventually attributed to a normal sound of combustion on this relatively high-power version of the engine. i now wonder if 100,00 km back, this was the start of the problem?

As yet, I haven't driven the car enough to determine if that 'click' is still there.....probably after the head has been checked after 1000 km.

BTW - This is just in time for the up-coming cool dry season and camping/touring in Laos and Thailand.
if anyone is interested please contact me for details.

From my experiences, there are three primary reasons for a head cracking in the middle.

1) Overheating. It goes without saying, really, this is the most common cause for cracked heads. They usually crack between the combustion chamber and the water jacket but I've seen cracks between valve seats, across to the glow plug, injector ... overheating is probably the #1 enemy of these engines.

2) Mis-torqued head bolts. If you don't do them up properly, the tension across the head will be uneven and when the stress levels go up, the head will warp and crack.

3) Impacts. Usually a turbocharger that disintegrates with no intercooler present, but could also be a failing EGR tube or valve - the EGR tube will be a surprise, but the valve should cause a lot of trouble (power loss, smoke, noise) before it lets go. Valves usually don't fail on their own, it's the result of the guide being worn (shows as blue smoke on takeoff after idling the engine, eg at traffic lights) and eventually destroying the valve shaft.

Thanks for the input.....I'll bear this in mind. I might try and get the old head after all... Only probably more hassle than its worth.