Overheating GU 4.2 Diesel.....a possible reason has been put to me.

Submitted: Monday, May 09, 2005 at 14:36
ThreadID: 22807 Views:4466 Replies:11 FollowUps:16
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G'day all,
Just drove back to work after lunch and my local Repco mechanic mate pulled up behind me. He's the bloke I recently got to bend me up a piece of s/steel tube to make up a new bottom radiator hose arrangement. He said he'd been talking to a bloke in NT who had exactly the same problem with his 4.2 TD. This bloke had a bigger, aftermarket turbo on and it used to get real hot, especially towing a large trailer. Embarrassingly, a young bloke fixed it for him........
Take a look at the housing where the bottom radiator hose joins onto the motor. There is a banjo joint where the coolant connects to the turbo. The pipe goes from the banjo joint, along the top of the exhaust manifold and down to the turbo. I have always believed this was the cool water going from the cooling system INTO the turbo.....but of course, the coolant at that point (ie: just at the top of the bottom hose) is being SUCKED into the motor. Therefore, the water which has just been nicely cooled by this massive radiator I have installed, is being "superheated" by the 400 degree+ water coming out of the turbo; before it even gets into the motor at all.
This young bloke "simply" plugged the hole in the alloy fitting at the top of the bottom radiator hose and re-directed the pipe coming from the turbo, over to the top radiator hose. That way, the very hot water coming off the turbo, is going directly into the radiator instead of the motor.

Apparently, this bloke has NEVER had a problem ever since. I don't know any names of the blokes involved, but it gives us more things to consider.

Ken....it's a bit like what you were saying about the Pirahna shower they installed in LUCY.....red-hot water going in; it's gotta heat things up eh?


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Reply By: Nudenut - Monday, May 09, 2005 at 14:54

Monday, May 09, 2005 at 14:54
so your adding/injecting heated water to a point somewhere between the radiator outlet and motor inlet?
AnswerID: 110456

Follow Up By: Member - Roachie (SA) - Monday, May 09, 2005 at 15:01

Monday, May 09, 2005 at 15:01
Don't lets start that debate again Nudie.....

But you're right, at the moment the really hot water from the turbo is being sucked into the system before it gets a chance to cool the motor down, thereby negating the cooling effect the radiator has just had on that water.
FollowupID: 366964

Follow Up By: Nudenut - Monday, May 09, 2005 at 15:34

Monday, May 09, 2005 at 15:34
thats a really dumb thing to do eh?

and hold on ..you started this......hahaha
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Reply By: Lone Wolf - Monday, May 09, 2005 at 15:35

Monday, May 09, 2005 at 15:35
Let me see if I've got this right.

The coolant flow, if I remember, is from the top of your block, down through the radiator, and returns into the bottom of the block?

Now, the Banjo "T" allows a small amount of cooled radiator water to be directed to the turbo.

Where does it go from there?

AnswerID: 110462

Follow Up By: Member - Roachie (SA) - Monday, May 09, 2005 at 15:48

Monday, May 09, 2005 at 15:48
No Wolfie, That's what I used to think....that some of the cooled water from the bottom hose (just before it re-enters the engine near the water pump) went thru the turbo. It made sense to me that the turbo would be fed the cooest possible water.

But NO, NO......that water in the bottom hose is NOT under pressure; it is being sucked up into the motor and therfore it makes sense that the banjo joint is actually directing water back into the system FROM the turbo, not the other way round. There is another junction where the water is coming out of the back of the block into the turbo (which I always thought was going INTO the block).

So, like I said, it seems the brilliant designers at Nissan have done a fine job of making a system whereby the coolest water is being "contaminated" with water from a 400 degree+ turbo BEFORE it evens gets a chance to get into the donk to do any cooling in there.
FollowupID: 366973

Follow Up By: Lone Wolf - Monday, May 09, 2005 at 15:56

Monday, May 09, 2005 at 15:56
Goodness me, it almost seems like we're moving into the realms of quantum physics, and throw in a bit of chaos theory as well!

This is going to be a hard one to nut out on pen & paper, bit like the theory of light...... wave or particle......

However, it has been suggested that this is a tangible problem, and that there has been a tangible fix........ I reckon go with it...........

Book a Sunday morning with your spanner dude, re-plumb, drive a little bit..... drive some more...... drive lots more............. and....... hopefully.......... nail this bugger once and for all!!

Best of luck, and if it works, I reckon we all need to do a whip around for you...... you have spent sooooooo much money & time on this....lol!!


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Follow Up By: GUPatrol - Monday, May 09, 2005 at 16:16

Monday, May 09, 2005 at 16:16
Roachie, Wolfie,

Sorry to dissapoint you but no, that is not the fix, GQ's were overheating (with that engine) for years before the GU even came out did not have that pipe!!

The latest 2003 on 4.2 GU does not have that pipe (the one with the longer radiator) as the turbo is not water cooled. They still overheat though...

By all means, go for it and modify further as it may help... but don't you think that the engineers would have done all the research?

The research came to the conclusion that the engine cannot dissipate heat therefore the tuning stops at a certain point (that is why they come so detuned from factory).

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Follow Up By: GUPatrol - Monday, May 09, 2005 at 16:39

Monday, May 09, 2005 at 16:39
Roachie, Wolfie,

Further to my previous post, the engine does not suck from that pipe, in fact the engine does not suck at all, the water pump moves the water around and does so by sucking from the block right in front of Cyl no 1, not the bottom radiator hose, it then pushes the water out to the top rad hose, as it travels through the rad and cools it is then continually being pushed through the bottom rad pipe and into the engine, in that process the turbo is getting its cool water from that pipe, the turbo hot side is on the bottom and it goes straight to the block and joins the hot water stream which is sucked by the water pump and the process is repeated.
FollowupID: 366982

Follow Up By: Lone Wolf - Monday, May 09, 2005 at 16:57

Monday, May 09, 2005 at 16:57
Bugger Bill!!!

I thought you had nailed this thing.

Bugger..... bugger..... bugger....

I know...... put cold water in the radiator in the morning.

FollowupID: 366984

Reply By: snowman - Monday, May 09, 2005 at 18:02

Monday, May 09, 2005 at 18:02
Hi Roachie,
I would have thought that by puting the outlet from the turbo to the top radiator hose you would be putting that end under the same pressure as the supply for the turbo. Therefor there would be NO flow through the turbo. There would have to be a pressure differences between the top of radiator and the bottom and that would be why you have wire coils in bottom radiator hoses to stop them collapsing from the suction. If you think that the return coolant from the turbo is an issue maybe fit some type of heat exchanger before it returns into the banjo fitting or block coolant suppy to turbo to see if it does make a differences.

Cheers Dave
AnswerID: 110490

Follow Up By: snowman - Monday, May 09, 2005 at 18:16

Monday, May 09, 2005 at 18:16
Hi Roachie,
Just one other thing that might be worth a thought. I read that you have fitted a " massive Radatior", did you upgrade the water pump to flow more water? The standard pump might not flow enough water through the radiator to use the benifit of the larger radiator.

Cheers Dave
FollowupID: 366992

Follow Up By: Member - Roachie (SA) - Monday, May 09, 2005 at 21:56

Monday, May 09, 2005 at 21:56
Thanks Dave,
I have been considering putting in a Davies Craig electric water pump in the bottom radiator hose which I could switch on if it looks like things are heating up too much......but then people also say that if the water is circulating too fast (like it would if I totally removed the thermostat), then the water would go too fast to be able to pick up heat from the motor and it would still overheat.
That's another thing i can try later anyway, but really, since i've done the last few mods, it has not been hot enough to know for sure whether I've cured the problem, but it certainly hasn't been getting as hot as it was a month or so ago.
Cya mate
FollowupID: 367035

Reply By: Exploder - Monday, May 09, 2005 at 18:29

Monday, May 09, 2005 at 18:29
Hello Roachie

So the patrol is still cooking even with the water wetter in it and after the diesel flush treatment, or is this just something else you are doing to stabilise the running temperature a bit more?

It seems like a fairly silly design to have boiling water coming out of the turbo and then mixing with the water going into the engine

Maybe you could put a mini radiator on the turbo ( :
AnswerID: 110496

Follow Up By: Member - Roachie (SA) - Monday, May 09, 2005 at 22:03

Monday, May 09, 2005 at 22:03
G'day mate,
After reading some of the other responses here, I'm not so sure now about the direction of the water flow to/from the turbo; maybe I was right all along. Only way to check would be to undo the banjo joint on one end (near the top of the bottom radiator hose is the easiest to access....then start the cold motor and with my thumb over the hole where the bolt goes, see if water spits out of the banjo joint (ie: from the turbo).
Not really having any overheating problems now, but OE gauge does still move up a bit when I push hard, but then the VDO gauge is only showing about 110c, which is okay by all accounts anyway. So maybe all this "issue" has just been a result of a useless Nissan gauge alone.
FollowupID: 367040

Reply By: G.T. - Tuesday, May 10, 2005 at 16:23

Tuesday, May 10, 2005 at 16:23
Out of curiosity, did the new thermostat have a `foot` valve or not? You mentioned in a previous post that the old thermostat did not open as much as the new one. If your vehicle ( as I suspect ) has a `foot` valve on the thermostat ,it would explain to me that if the old thermostat ,by not opening fully ,was not blocking off the by pass properly and letting hot water straight back into the engine block. You seem to be reasonably satisified that the overheating is a `gauge` problem.
Some motors can create a vortex action in the by pass and the water gets virtually `sucked` back into the motor. This was a particular problem with Tasman / Kimberly cars some 30 yrs ago, if the thermostat was either removed, replaced with one without a `foot` valve, or not opening fully. They would overheat straight away. I suspect that replacing the thermostat has made a difference to your problem. If your thermostat does not have a `foot`valve then I guess it might be back to the `drawing board`. I will be interested to hear your comments. Regards G.T.
AnswerID: 110647

Follow Up By: Member - Roachie (SA) - Tuesday, May 10, 2005 at 23:48

Tuesday, May 10, 2005 at 23:48
Gday GT,
Yes mate it has the foot valve; which I must admit, I didn't know the significance of until yesterday when the Repco mechanic bloke said that I must keep the thermostat in the GU or it would just keep routing the water through the motor; not the radiator.
FollowupID: 367177

Reply By: Barnray - Tuesday, May 10, 2005 at 20:45

Tuesday, May 10, 2005 at 20:45
There is a fix from Nissan, I am not 100% sure of the exact details but they adjust the air con so it runs a little warmer (less heat up front) and adjust injection timimg and amount of fuel. They repaired a turbo 4.2 at a local dealer that was heating up under heavy load up mountains (cattle trailer loaded with calves or bulls).It now runs much better, better power and normal operating temps, I suggest you try and find a Nissan Dealer mechanic and ply him with the universal lubricant and make him talk. Good Luck I hope the info helps Barnray
AnswerID: 110698

Follow Up By: Member - Roachie (SA) - Tuesday, May 10, 2005 at 23:51

Tuesday, May 10, 2005 at 23:51
Thanks Barnray,
I will try to find a good Nissan workshop bloke. I had one here, but recently pyssed off in his GQ for WA.
Cheers mate
FollowupID: 367178

Reply By: waterpumpman- Monday, Jun 06, 2005 at 01:42

Monday, Jun 06, 2005 at 01:42
Hi Guys, I have been reading with interest your dilemas with overheating and wondered if any one has actually flow and pressure tested the factory and aftermarket waterpumps because I made a waterpump test machine and was shocked to find out that all of the pumps I have tested so far make really great milkshakes but this can't be seen due to the non transparent nature of engines and blocks! It does not take a rocket scientist to understand that an aerated coolant won't cut the mustard!! A bigger radiator won't help as the problem is shifting the heat to be dissipated from the engine to the radiator. I have subsequently hand made new pump impellers with great success in most cases.
I hope this gives you some food for thought............
Happy motoring.
AnswerID: 114497

Follow Up By: Member - Roachie (SA) - Tuesday, Jun 07, 2005 at 10:11

Tuesday, Jun 07, 2005 at 10:11
Thanks for your interest and response waterpumpman.
Now you've got me wondering again......does the standard water pump have the necessary "ooomff" to be able to circulate the amount of coolant in the system; especially in my case as I have fitted a radiator which is twice the capacity of the original?
I'd be interested in more info from you; and I'm very certain others would too, as this has been an ongoing problem for quite a few of us.
I had previously thought about fitting a Davies Craig in-line water pump in the bottom radiator hose and simply manually operating this pump when I see the temp gauge getting up a bit.
What are your thoughts about that idea?
If possible, would you mind posting your ideas and comments in a new post, perhaps referring back to this post number.....the trouble being that this one is well past it's use-by date now and no-one is likely to come across it.
Thanks for your assistance.
FollowupID: 370551

Reply By: waterpumpman- Tuesday, Jun 07, 2005 at 23:20

Tuesday, Jun 07, 2005 at 23:20
Hi Roachie
You are well justified to start thinking about your cooling system again!!! A larger radiator is like a bandaid on a shark bite when you consider that the original problem was most probably partially caused by a pump which was and still is not up to the task. Your idea about the electric waterpump is of no value for many reasons, for example, 1: what if you forget to switch it on?
2: what happens all the time it is swithed off?
3: your existing pump will have to do more work to pass water through it as well.
4: Having two impellers to agitate the coolant causing double the aeration wouldn't be heading in the right direction!
5: the extra pump won't work harder as the engine load increases.
Lets start from a new angle........ How about a cooling system which allowed you to diagnose what was going on while you were driving.... Sounds to good to be true, Not really and once you have a pump on there with some integrity, I will show you how as I am scared to suggest anything until you have a pump of known performance fitted.
I will work on an explanation for a new thread asap. Feel free to keep up the questions and i will attempt to answer them for you.
AnswerID: 114846

Follow Up By: Member - Roachie (SA) - Wednesday, Jun 08, 2005 at 12:01

Wednesday, Jun 08, 2005 at 12:01
Well waterpumpman, you certainly have got me intrigued and I am looking forward to seeing more of what you have got to say.

I don't profess to be an expert on anything at all, but I do read a lot of stuff and try to make head from tail of it all. In that regard, I had been looking at the Davies Craig web site for info on their EWP (electric water pump). According to them, you have 3 choices of fitment of their pump.
1. Fit the pump and an electronic controller....remove the standard impeller and thermostat. The electronics would determine when the pump needed to be switched on and what voltage needed to be applied so that it would pump suficent coolant to maintain the pre-set optimum operating temperature. They claim the EWP can pump up to 80 litres/minute which I would imagine would be sufficient. They also talk about removing the belt that operates the standard water pump (assuming it does not also drive the cooling fan etc).
2. Fit the EWP with the existing standard water pump still in place. The EWP could be controlled by a thermatic switch which would switch it on when the coolant reached a pre-set temp (ie: when it starts to get too hot). I would prefer to do it this way, but rely on my own nouse to switch the pump on, having regard to the VDO temp gauge I have fitted and which I watch like a hawk.
3. You can also have the pump wired to be on permanently. This is recommeded for race cars and other very heavy use patterns etc.

I take your point about the slightly extra load on the standard water pump when the EWP is not switched on, but I still like the idea of being able to give the coolant circulation a bit of a boost.

Having said that, I still go back to what i said at the start; that I'm very interested in anything you have to contribute and your suggested solution/s.

Thanks again.

FollowupID: 370677

Reply By: waterpumpman- Wednesday, Jun 08, 2005 at 14:10

Wednesday, Jun 08, 2005 at 14:10
Roachie Roachie
Where do I begin now. You have read what is available commercially and I guess it is like deja vu for me ( about 15 years ago. ) You need to forget anything that you have ever read on this subject and start from the beginning using basic logic and commom sense together with practical testing and application of your good results.
To give you an example of what I am talking about, bubbles float and if your top radiator hose dosn't run uphill to the radiator, it will create a steam trap with water passing through the bottom half and this steam trap will grow and grow lowering the coolant level until it gets down to the level of the radiator cap. You will have to imagine your cooling system as an aquarium to visualise what I am referring to. If the manufacturers got it wrong it is time to make alterations to rectify their poor workmanship...........Therefore, the radiator cap must be in absolutely the highest possible spot otherwise your system will not work at its best.
Another point is that the coolant flow should not be responsible for controlling the temperature!!!!!!!!!!!!!!!!!! The coolant flow should be enough to maintain a constant temp with minimal nucleat boiling to prevent engine damage. If you think about what I have just written and can't see that what I am saying is different from what you have already read, it is time to stop... get a cuppa and then reread... I think you can make great improvements to your system with a little help. The benefits will mean, longer engine life, reduced emissions, lower fuel consumption, and a bit more power as well. (that would be hard to take wouldn't it )
Have I got your full attention yet? You can get me audiofurn@iprimus.com.au



Ps: I still say that the electric idea is a way for them to lighten your wallet while they baffle you with bull.... I have pulled several of them off to fix the temp control problems.
AnswerID: 114893

Follow Up By: Member - Roachie (SA) - Wednesday, Jun 08, 2005 at 17:28

Wednesday, Jun 08, 2005 at 17:28
Okay waterpumpman, you're still "teasing" me with your possible solution/s and the intrigue continues to build.
My radiator cap is certainly the highest point in my cooling system; no doubt about that. As for whether I am suffering from any cavitation or bubbling in the coolant, I have no way of knowing this......maybe if some kind/smart person would manufacture a transparent upper radiator hose a lot of these questions could be answered...hahaha
What exactly would you be proposing as a solution? You mentioned early in the piece that you had done work on new impeller design. Do you make these commercially? What is involved?
Looking forward to getting to the bottom of all this.
Cheers mate
FollowupID: 370703

Follow Up By: GUPatrol - Wednesday, Jun 08, 2005 at 19:30

Wednesday, Jun 08, 2005 at 19:30
I read with interest!! but... what about those sports cars which have the radiator much lower than the engine block? They still work and very efficiently... although they do have a de-ariator sitting somewhere up in the suspension tower on close to the firewall. THe new 4.2 patrols have such deariator and a new radiator design and yet they still overheat...

Now I am going to tell you the story of my friend with a 4.2 TD GQ.
He tried (we as I helped him) and others as he worked in the automotive industry, everything, when I say everything it means the lot...
Radiator, electric fan, new viscous, thermostats, with without, head (new head), hoses, not sucking, bleeding etc etc...
Then he went a little further and increased the size of the water galleries inside the engine, then he got to talk to someone in Melbourne (I think) who mentioned the water pump and also a dearieator kit which is supposed to get rid of steam in certain parts of the engine.
There was a test method included in the kit which we did one afternoon, I can't remember exactly but the amount of bubbles and soda looking water was amazing.... We then replaced the water pump with this new one and its new impeller, and also the kit which took a whole afternoon to fit, the "after" test was much better not as many bubbles, but still overheating although slightly better....
He then decided to make a radical change and modify the way the water circulates (in other words he modified it to work like the new 3.0L engines and many falcons etc) which is more efficient??
That had an effect but not yet OK, his GQ was still getting hot but not as much.
I will add that everything was in perfect order, the engine performance was OK, timing was checked, the pump had been fully rebuilt and the injectors had been done etc...
The conclusion while towing a car trailer with a broken down Rangie on it from Fraser Island back to home was that if he backed off it would not overheat which makes it in his words not good enough (and I agree in a way) because up hills you can't backoff but I would be very interested to know what is that makes these engines rise temperature.
One more thing, at some point he even removed the grill, bullbar and everything to allow more airflow and the test proved to be fruitless....
In my opinion having seen many different engine designs and many engines pulled apart, this engine does not have the capacity to get rid of heat by design, the cast iron head and block don't have big enough galleries to get rid of the heat generated by the applications we use it on today, it was designed to be pulling a bus a slow speeds in a naturally aspirated form.
But I welcome other's opinions... as I am not an expert and my theory cannot be tested unless we can talk to the engineer who designed it.
FollowupID: 370720

Reply By: waterpumpman- Thursday, Jun 09, 2005 at 13:35

Thursday, Jun 09, 2005 at 13:35
Hi Roachie and Will
There are explainations for most things and the sports car senario with the low radiator even if it is mounted flat can work if the radiator cap is mounted on a header tank or a de-aeration tank which has to be mounted as high as possible in relation to the engine. Along with this as I stated before there must be no built in air traps or the system will not work properly. The top hose layout is crucial!!!!!!!!The new vehicles which use the low radiator type of system still have a multitude of other problems such as built in steam pockets, head gaskets which are inappropriatly drilled for coolant flow, inferior waterpumps, poor top hose layout, inadequate header tank size or no header tank at all and the like. An example of a good radiator design is the early F100 with its large top tank allowing de-aeration in the highest piont in the system.
If you get directly in touch with me I can give you much more information and yes I do hand made impellers and waterpump upgrades, custom header tanks, de-aeration tanks etc. Each vehicle may require very different modifications to make them more reliable and there are times like Will had with the boiler he was working on where it all seemed impossible. To date I have not had a vehicle which I have not been able to make major improvements to, however, there have been times when the customer has not had the patience or money to pay for the enormous amount of time required to make their vehicle into a useble proposition.
In most cases an improved waterpump and careful attention to top hose layout together with steam bleeders can make a great deal of improvement. If the extra system Will fitted was an ecotrans unit, then he was on the right track! There are some inferior units out there which just dont measure up!
When turbos are involved it can complicate things because the superheated water if fed into the suction side of the pump may cause severe cavitation with catastrophic outcomes. Vehicle airflow dynamics also come into play but before I look at this aspect, I set up a proper bypass flow system so that I can diagnose where the problem is under driving conditions. Will I do agree with you that some engines have inappropriately designed water galleys, however, so far I have been able to improve things enough in most cases.


Waterpumpman ( audiofurn@iprimus.com.au )
AnswerID: 115058

Reply By: Member - Camper (SA) - Thursday, Jun 09, 2005 at 22:47

Thursday, Jun 09, 2005 at 22:47
Geez Roachie you will be able to publish this as a saga to rival Beowulf.
Back to the hypothesised flow to and from the turbo. You could test this by measuring the temp of the pipe both sides of the turbo (your hand might even be enough). The return side would have to be noticably hotter, which means you then know which way the juice is flowing. Then you might know how much credence to give the theory that the turbo is creating the problem.
AnswerID: 115145

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