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  #1  
Old January 7th, 2005, 03:05 AM
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Trevor Tarr
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Trevor Tarr
1997 D-90 4.6 NAS ST
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Baffling Overheating Saga

Rover sleuth gurus, here's a real head-scratcher. I'm desparately trying to figure out why my '97 D-90 still overheats, after what seems like every possible fix....

For its first 130,000 miles or so, my temperature guage never deviated from the exact middle of its range, until....

One day, on the highway, my water pump bearings gave out. I smelled coolant, looked down, and noticed the temperature guage starting to creep up. I pulled over, figured out what was wrong, and had the truck towed to my mechanic (Eddie Bostock at West Coast Rovers).

They replaced the water pump, and I headed home. After about 15 minutes on the highway, I started overheating again, so had it towed back. After a day of diagnostics, Eddie determined that the guage was reading hot--but not the engine. Faulty sender, he figured.

So I picked up the truck, drove it home (with the guage reading hot again), and replaced the sender (the guage sender, not the ECU sender). But that didn't fix the problem.

So I towed the truck a third time down to WCR. Eddie determined that the cooling system was holding pressure, and that there were no exhaust gasses in the coolant, then replaced the thermostat and overflow tank cap, recored the radiator, and swapped out the viscous fan clutch. But the truck still overheated, although now it wasn't happening every time I drove it, but just under extra load (like on long uphill stretches), and especially at slow speeds.

So we figured all that was left was the head gasket. Did that pricey job, but ... still overheating.

So, everything else now ruled out, I got the worst-case news: the conclusion that all this was due to a pinhole fracture in the cylinder block. So ... $7,500 later, I've got a new short block (which, in the process, I upgraded from the 4.0 to a 4.6).

And ... I'm still running hot. Everything is OK 90% of the time, on the highway, even in rush hour, with the a/c running, and driving around town. It's just going up long hills, at speeds under 30 mph, that I'll consistently run hot. To me, that sounded like the viscous coupling not engaging, in low-speed situations where there wasn't much ram-air effect.

So, today, in goes a new fan clutch. And ... no improvement.

I'm absolutely at my wits'-end here. What could we have missed???

Trevor Tarr
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  #2  
Old January 7th, 2005, 07:28 AM
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jim pendleton
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You need to have a better radiator built for the larger engine. The radiator was prolly barely cooling the old lump. You can have your original recored to larger specs.

JP
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  #3  
Old January 7th, 2005, 07:35 AM
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Sorry to hear that...

I'd suggest you get some electrical fans with the automatic regulators...
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  #4  
Old January 7th, 2005, 07:44 AM
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I agree with Jim and was going to ask, when they re-cored, did they go to a 4 core rather than a 3 core? Greatly helped my cooling issues. Also I have gone through 3 clutch fans since owning the D90, 2 of them in the past year so there is a possibility that you still could have gotten a bad one. If i have to replace it again once it gets out of the work warranty, I will just replace mine with electric fans. Other than that, sounds like most of the other bases have been covered that I had to go through with my own cooling issues.
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  #5  
Old January 7th, 2005, 03:28 PM
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Jan-Dirk Roodbol
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your problem started by replacing the water pump. Did they replaced the right one?
I noticed that here in europe different types are on the market. Recognized by a different number/shape of the fan.
is your temperature gauge itself in a good order ?
how is the thermostat?
are you sure that there is no air lock in the system?
I found out that my expansion tank was not working well,
cause: from the top of the radiator, a hose is going to the expansion tank. The metal tube on the inside of the tank was to short, so when the system was cooled, only air was sucked back into the radiator.
Maybe you can find your problem in this part
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  #6  
Old January 7th, 2005, 03:52 PM
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Thanks everyone for your feedback!

I realize the 4.6 may have greater cooling demands than the 4.0. But the engine was already running hot BEFORE the new engine was installed....

The replacement water pump was a Land Rover part, not an aftermarket pump. And, before the last-resort engine replacement, Eddie did try a second water pump, just in case.

I haven't replace the temperature guage, but that's not the problem: the engine reads hot not just on the guage, but through the OBD-II software I run on my laptop through the diagnostic port (which gets it data from a separate sender than the guage). Going slowly uphill, the temperature climbs to about 220 degrees.

I've replace the thermostat twice.

I'll double-check the expansion tank.

To me, this is the significant clue: the engine only runs hot when I'm driving SLOWLY (e.g., no ram-air cooling effect on the radiator) UPHILL (e.g., additional load). Even up steep hills, when I speed up, the engine cools back down. That's what keeps pointing me back to the fan and viscous coupling....

Trevor
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  #7  
Old January 7th, 2005, 05:49 PM
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Jason Herring
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I hate viscous fan clutches with the passionate fire of 1,000 burning suns I went dual fan electric - not too much more expensive than the factory viscous clutch part, and they will rob you of less horsepower.... oh, and pull alot more air through the radiator than the mechanical fan ever did...
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  #8  
Old January 7th, 2005, 07:32 PM
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Doug Walker
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Trevor,

220 for a 4.6 is not overheating, imho. Mike Green at WCB has a 4.6 that runs up to 220 on long pulls. Low speed means less ram air getting into the rad, so that's why it goes up at slow speeds. My 5.0 goes to 225 on a long pull, but I get uncomfortalbe in that range, needless to say. The NAS 110 manual says backpressure from bad muffler can cause overheating. Anticipating the desert heat next summer, my next action is to install twin 3 inch exhausts, port match the manifolds, and install super high flow cats. You might try Larry at 4 Oaks, who has a source for a race technology rad core (used by the Morgan dealer out here to cool off the horribly inefficient system in the late model Morgans), which I installed and finally got me into a safe range to drive the 5 liter TVR around town and on long trips with some confidence. This was after installing a set of Flexalite twin electric fans. I'm also going to wire a separate circuit to switch on the AC fan without AC running.

That's the plan. You're welcome to come look at my rig anytiime. West L.A.

DW
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  #9  
Old January 9th, 2005, 02:41 PM
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Brian Bonner
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You need to be more specific. what dual fans? The flexalite dual 12" fans do not pull as much air as the factory fan. speking to the company they were clear that no e;lectgric fan will out perform the mechanical fans today.

Quote:
Originally Posted by jaherring
I hate viscous fan clutches with the passionate fire of 1,000 burning suns I went dual fan electric - not too much more expensive than the factory viscous clutch part, and they will rob you of less horsepower.... oh, and pull alot more air through the radiator than the mechanical fan ever did...
Follow-up Post:

OK first you stated that the actual temperature in the radiator was not running hot. If so this guy robbed you blind. My first recommendation would have been to toss that facotry gauge and get a VDO which will drop right in place. Use a sender that is 1/2x20 for it. Then you have an acurate gauge. You gauge could be toast. But you can tell by just putting a mechanical temperature gauge in the fluid while it is running. do this first in the expansion tank. If tha is fine then after it is cool open the radiator plug and heat up the engine again and check it.

At any rate I always recommend getting a real temperature gauge an oil pressure gauge(this may save your engine one day) because the oil pressure light does not come on till it is down near zero. So if you get the common problem of the pressure relief valve sticking in your oil pump you will be running around at about 5psi with no warning.

If you have a winch you need a volt gauge as well. to make sure you never discharge your batteries below 11 volts
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  #10  
Old January 9th, 2005, 06:55 PM
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Thanks again to all who've put thought into this puzzle of mine. Doug, maybe I should consider 220 (which I only reach on long slow up-hills) OK. I'm just baffled why it's started running hot like that now, and never did before. And it's not the 4.6 upgrade, because I started having this problem BEFORE the new engine, and before the head gasket work. Ever since my water pump failed, I've been overheating. Originally, it was all the time, and now (after having the radiator rodded-out), it's just on the slow uphills. But it all started with the water pump bearing failure.

Maybe I should just give up trying to figure out the cause-and-effect here, and just focus on solving the problem and moving on....

I'll look into the exhaut back-pressure issue, and consider upgrading my radiator and installing a manual switch for the electric a/c fan. Thanks again.

Brian, others have also suggested replacing the LR temp guage. That may be a good idea, but I'm getting my temps from two sources. Not just the guage, but also a digital readout from the ECU, through my OBD-II software. The guage and ECU get their data from two separate senders. So I'm pretty sure the engine really is running hotter than I'd expect it to.

And I definitely agree about the auxiliary guages. I've installed oil pressure, voltage, and current guages. The oil pressure guage I spent a lot of energy trying to plump with a t-fitting into the oil pump location where the stock pressure switch sits. I could never get anything to work without leaking. Where have you located your oil pressure sender?
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  #11  
Old January 9th, 2005, 07:21 PM
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L C
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I have put some lots of thought into get gauges thing as well. Is there a set type of gauges you bought for your truck or were they just a standard? Do you recommend any or just buy any type?
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  #12  
Old January 9th, 2005, 08:31 PM
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Dave Souza
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Just a thought, but I've had some overheating issues as well. My problem is different, but one note might be of interest to you, or others reading this thread in the future. I had a radiator shop build me a custom core using my existing radiator. It was a 4 row, flat fin design, that *should* have had 30% more cooling capacity than the stock radiator. However, upon installing this radiator, my truck would heat up on long hills, and really at any high speed on the highway. After swaping out another radiator (another 4 row re-core, this one to stock specs though, just another row added) the truck runs fine. So whatever they did on the first radiator (too big of tubes, I suspect) it wasn't cooling the truck under load. Our best guess is it was flowing TOO much, and didn't give the water enough time in the radiator to cool down. Just an odd situation that I thought I'd mention.

Follow-up Post:

Oh, and for gauges, I've installed the VDO Vision series.... bought from http://www.egauges.com. They fit perfectly, and the lighting is fantastic. No fogging either. I love them
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  #13  
Old January 9th, 2005, 09:12 PM
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Robert Dassler
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Trevor,
I put a VDO temp gauge and sender in my D-90 a couple of years ago...driving in the mountains I can push 210F. Putting a new stock radiator and t-stat in brought it down a bit.
Two other thoughts...when the original waterpump went out and started this whole mess, did it damage the front cover? The cover has coolant passages and a space for the pump to work. If that cavity was damaged when the pump failed, you could alter the coolant flow. I assume you reused the original cover when you did the engine swap. Also, I'm not sure it's possible to reverse it on a D-90...but is the cooling fan installed on the viscous unit the right way around? I have seen fans installed backwards on other vehicles cause slow speed overheating as the fan is trying to push the air from under the hood out the grill...at idle it will work, at high speed it will work but at slow speed the airflow becomes equal and the vehicle overheats.

One other thing...you are running a full undamaged radiator shroud, right?...the fan won't work correctly without it.
Rob
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  #14  
Old January 9th, 2005, 11:02 PM
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Trevor Tarr
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Rob, I'll check the front cover. That's a possibility. It would make a lot more sense if all this tied back to something damaged by the original water-pump failure ... rather than a coincidental secondary failure.

The fan is blowing in the correct direction, sucking air through the radiator from outside. And, yes, my radiator shroud is intact.

Trevor
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  #15  
Old January 10th, 2005, 12:31 AM
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Just get a BIG, NEW radiator built. NAPA will build you whatever you want at a decent price. The LR radiators are inatiquate for the stock engines.
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Old January 10th, 2005, 12:49 AM
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Ok, here's just some random thoughts.

What is in front of the radiator? Winch, winch bumper or any other stuff? It might be an issue of airflow through the radiator. I know my current brushguard has some expanded steel screen in it to protect the radiator, but I am considering removing it or making it removable.

Another question, how is the tranny temp? Never been under the hood of a '97, but do they use an in-radiator cooler for the tranny?

Have you considered upgrading the oil cooling system as well?

Also, here is one I never really thought of until now. Does running a snorkle or other cold-air system actually increase under-hood heat? With the engine sucking all that hot air down into the cylinders in a stock setup, does that have an effect on the under-hood temp at all?

-Hans
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  #17  
Old January 10th, 2005, 03:23 PM
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I talked to a guy this weekend that runs a couple of aggressive off road trucks and a high performance offshore yacht. He says there's a shop in Torrance that builds aluminum radiators for west coast Nascar teams and they'd build one for the Defender, no problem. He also said there's a speed shop in the San Gabriel valley that does excellent custom header and exhaust work, and could easily build a whole header/exhaust system for the Ds. No mention of price..., but I think I'll follow up in the spring and investigate. I'm fine with my temps now, just worried about low speed uphill crawling in desert heat this summer....

Doug W.
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  #18  
Old January 10th, 2005, 04:07 PM
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Sorry I didn't know about the ECU since mine is obdI. I took one of the plugs off the oil pump. there are 2 plugs you can use. I had it tapped for 1/4" npt and installed my sender in it. so now I have both senders. If you look at the housing that the sender sits in you will see 2rather large bolts and one that is bigger on the bottom the real big one on the bottom is for the pressure relief do not mess with that. You will know if you acidentally remove that as there is a spring in it. the other 2 can be used.

Quote:
Originally Posted by Trevor Tarr

Brian, others have also suggested replacing the LR temp guage. That may be a good idea, but I'm getting my temps from two sources. Not just the guage, but also a digital readout from the ECU, through my OBD-II software. The guage and ECU get their data from two separate senders. So I'm pretty sure the engine really is running hotter than I'd expect it to.

And I definitely agree about the auxiliary guages. I've installed oil pressure, voltage, and current guages. The oil pressure guage I spent a lot of energy trying to plump with a t-fitting into the oil pump location where the stock pressure switch sits. I could never get anything to work without leaking. Where have you located your oil pressure sender?
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  #19  
Old January 10th, 2005, 05:28 PM
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Brian, I wonder if the '94 and '97 oil pumps are the same? I've heard others also describe removeable "plugs," but I can't find anything like that on my oil pump. Do the bolts just unscrew? Do the 97's have them?
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  #20  
Old January 11th, 2005, 01:55 PM
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I cannot be sure. But IO would bet it still uses the 215 oil pump. The 94, 95 and classic RR all have the same pump. Just look at the housing. They look like bolts. But not thee ones actuall attaching the pump



Quote:
Originally Posted by Trevor Tarr
Brian, I wonder if the '94 and '97 oil pumps are the same? I've heard others also describe removeable "plugs," but I can't find anything like that on my oil pump. Do the bolts just unscrew? Do the 97's have them?
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