TD27T overheating

Hi all, noob here that needs some help.
I suspect that my 1996 D21 Navara 2.7 has a Terrano engine but I am not sure how to identify it from a NA 2.7 with an aftermarket turbo.

One of the reasons I suspect this is that it has a sensor on the thermostat housing that does not have a corresponding plug in the loom but could be from a different model I guess.

While some of the turbo components appear factory, some are definately homemade.

My problem is that when driving on the highway at 100-110kph the car runs great until I have a hill to contend with, then the temp climbs to above 3/4 on the gauge, then as I go downhill again, the temp returns to just below half on the gauge and stays this way until I get to another hill.

It is not using any water, and only heats up when under load on hills, at all other times it behaves flawlessly.

I have checked the radiator for blockages and water runs freely though it, then checked the thermostat in boiling water and it opens, but didnt have a temp gauge to test the temperature, the shroud is in good nick, nothing is blocking the radiator, the belts are tensioned but I havent checked the viscous coupling since I thought at that speed it would be having almost no effect anyway. My next step is to check the water pump, since the corrosion in the thermostat housing could be a clue as to the condition of the water pump impeller.

What I have noticed is that the bottom flange of the thermostat acts a bypass to ensure that all the coolant goes to the radiator instead of circulating around the block and has a corresponding sealing surface inside the thermostat housing once the thermostat is open, this sealing surface is pitted and I am not sure what effect this has on the operation of the cooling system but I suspect not a positive one.

Is this a common TD27 problem?

Any help is appreciated and any photos of the two engines would be a great help.

Is there a cross-over pipe on the intake side that has the word TURBO cast into it? It crosses over the rocker cover. That's from a factory Terrano TD27T.

With the overheating, EGT will peak under load with a bad fuel tune. Try getting the pump dyno tuned

Yeah it has "Turbo" on the crossover pipe, and I discovered a broken vaccuum hose that comes from somewhere down low on the drivers side of the engine around the injector pump, and if I had better light I could see if it comes from the diaphram on the injector pump, perhaps for enrichment under boost?
This is something that has only occurred lately, so I hadn't considered fuel metering.

Sure its not a TD42. The overheat before the hill.

Going by what you have said, Id be pulling the water pump off.

I agree, the water pump will be coming off tomorrow if I get time.
I expect that the vanes on the pump may be corroded enough to stop efficient water circulation.
Did the thermostat housing theory makes sense at all? I couldn't explain it clearly but I can take some pics if needed.
There is a passage that allows water to bypass the radiator and circulate around the engine, until the thermostat opens fully, then the small disc on the bottom of the thermostat blocks this passage to make all the coolant travel through the radiator.
If this is not happening or at least is impaired, that could also cause the problem I am experiencing I think.

I will also be replacing the thermostat since I could not test it accurately.

I should have also mentioned that it had good quality coolant and was not low, and it had no air in the cooling system.

Mate for the water pump and the thermostat, use genuine when you can.

These parts have had alot more testing and development then some of the aftermarket stuff.

Second your comment on the pitting, if the thermostat housing is pitted. The water pump probably is to.

Sounds like good advice Dave, thanks for that.
I have been told in the past that GMB make most water pumps for the major manufacturers, have you heard of this?

If it was me, Id make sure atleast its made in Japan.

Cant say I have heard that, but doesn't mean its not true.

See what is written on the one you pull off.

Update: I changed the thermostat tohight and it seemed to help, but still watched the needle creep up.
Looks like the water pump will have to wait till tomorrow, but thought I would try the thermostat first.
I did notice the viscous fan coupling was freewheelijng after a 40 km drive, am I wrong in assuming that at 100kph the fan shoold be redundant by the volume of air passing over the radiator?
Does the TD27 rely this heavily on a fan clutch that is known to fail?
I doubt it.

Dave I believe thay are made in Japan, but you just never know these days, almost everything has "Made in China" stamped on it.
I will do a bit of research and let you know.
Thanks again for your help.
Tony

How freely does the fan spin ?

It should have some resistance.

Hmmm...it seems that GMB are at least made in Japan, not sure about the OEM though.

The fan spins with almost no resistance when hot.

When the engine is off ?

Sounds like the fan clutch is shot.

Yeah when its is switched off, thought it might be a little dangerous to test it while running......LOL

Does the fan play a role at highway speed? I thought it was only at low speed that it was needed.

The mechanical fan will operate when needed.

The fan clutch is attatched to the water pump anyway. So if you cange the pump, you get a new clutch.

I have the same prob with mine but it has the TD27 fitted with aftermarket turbo kit. I found my prob was the radiator (1 year old). I replaced it with a copper core 32mm from Red Devil Radiators for $365.

The clutch for the fan is part of the water pump and around $150 to $200 new. When you say it is over heating is when driving over 60 ks??

^ She's back.

Where you been hiding Linda.

Dave, now this time i will forgive you. lol So who's Linda pmsl.