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Morning Folks,

I currently own a 1992 ex-MOD hard-top 90 2.5na, which has recently developed a bit of an overcooling problemo!

No matter how far or hard I drive it, the temperature gauge never gets above a quarter of the way, the heaters blow cold and it's generally bit sluggish (yes, more than usual!). FYI the gauge used to sit firmly in the middle no matter what the weather!

I've bought 2 genuine thermostats, the original spec one and also the higher temp one. Both of which I have tested in water with an IR thermometer and confirmed working properly. Yet when fitted, I still have the same issue. I've even had the IR gun on the engine and that is only getting up to 66c!

Yesterday I took the truck to a local indy who has replaced the stat again and can't see anything else wrong with it.

Finally, I've also replaced the cable from the temp sensor to the gauge and crimped some nice shiny ends on it, just to make sure that it wasn't shorting anywhere. 

Any advice is greatly appreciated!

Cheers,

Tom

 

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I think there are few simple checks you can make to see what's happening. I presume your cooling system including heater matrix is clean and flushed so there is no rubbish in there.

Firstly - what is the opening temperature of the thermostats you have? I would also check them by putting them in a pan of water and slowly heat it up on a stove. Using a thermometer note at what temperature it starts to open to check the function. I have heard a few people comment that even new ones don't always open when they should.

Next, check for airlocks in the cooling system, particularly into the heater matrix.

Also worth checking the viscous fan turns freely when cold so you know it isn't binding.

Finally check for the correct operation and adjustment of the heater controls so that when you move the lever to hot it is actually fully opening the flap on the heater box. Then take it for a good long drive to get it up to temperature and you should have nice warm air coming through.

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Hi Monkie,

I have a 74c (original) and also an 82c (which was fitted to the winterized defenders). I've tested both in a pan with a thermometer and both open at the correct temps. 

Water is definitely flowing around the matrix as I've had the thermometer on that and the pipes to and from it. Hoses that should be warm, are warm, which hopefully rules out an airlock.

I re-vamped the heating system when I first bough the truck 2 years ago. This included heater cable adjustments, brand new heater matrix, foam seals, the lot. 

I've also removed the viscous fan a few weeks ago to see if it was that, however the results are just the same. 

The problem isn't just a cold heater, I believe that is a knock-on effect of the general cold engine temp and sluggishness. 

The engine used to get up to temp just fine and the heaters were actually great. This is a recent thing over the past few weeks where I cannot for the life of me warm the engine up.

 

Thanks,

Tom

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Okay, you have confirmed the thermostat and cable operation at the heater box so you know controls are functioning correctly. You can also discount a malfunctioning fan.

So the engine is running and obviously producing heat. When the engine has been running following a drive, do the coolant hoses feel hot to touch? Are you confident there is water in top hose to the radiator? 

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Thanks for the replies guys!

@monkie Header tank is at the correct level & when squeezing the top hose, it does feel like there is water in there, plus it slightly warms up.

 

@western This has crossed my mind. The only reason I am doubting it is because I did it in Oct 2019. Surely it wouldn't fail this early?

 

Cheers,

Tom

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24 minutes ago, western said:

Just a thought but is the water pump actually circulating the coolant 

That is another great point. One or two have been known to fail over the years :mellow:

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20 minutes ago, tomw92 said:

Thanks for the replies guys!

@monkie Header tank is at the correct level & when squeezing the top hose, it does feel like there is water in there, plus it slightly warms up.

 

@western This has crossed my mind. The only reason I am doubting it is because I did it in Oct 2019. Surely it wouldn't fail this early?

 

Cheers,

Tom

Anything could happen - did it arrive in a blue box by any chance which would strongly suggest it was a part made in Britain? By top hose, I mean the hose from the thermostat housing to the radiator. When you drained the coolant to swap the pump, did you also undo the plug on the block by the oil dipstick tube so the whole cooling system was completely empty? Also did you measure how much coolant you put back in to fill it so you know it took the full capacity with no dead spots?

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It was in a white box if I remember correctly, grabbed it from eBay for £39 new. Listing title is "Land Rover Defender 2.5L N/A Diesel & Petrol Water Pump Bearmach STC635". 

Yep, that little plug was a bugger to get off! Measured it out too. Well, as best I could with plastic jugs on the drive haha.

Cheers,

Tom

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Remove the belt and see how the pump feels by hand when you turn the pulley by hand. 

Did you undo the plug on top of the radiator to let the air out? Squeeze the hoses to see if coolant is in them.

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Hi Monkie,

Good thinking on the belt. When turning the pump by hand, what should I be feeling for? Just a smooth action? 
 

Yep, I even bought myself a shiny brass plug for the top of the rad after I chewed the original plastic one. 
 

Cheers,

Tom

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Yes. Check it feels smooth and no nasty noises of broken things. 

If that checks out okay, I would recheck everything suggested above. I think the capacity of the cooling system is 13 litres, but double check that in the manual. 

 

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Undo one of the heater hoses with the engine running, can help move an air lock and will show if the pump is moving water.  

If it's running very sluggish check air/fuel filters, has timing slipped, leaking injectors etc etc - could be the engine isn't producing enough power to heat up all that cast iron and big cooling system in the current low temps, even my tdi is struggling at the moment. 

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Turning the water pump over by hand will only reveal bad bearings.  You need to remove it to check the impeller is still secure on the shaft - it is not unknown for them to separate, so the spinning shaft fails to drive the impeller.

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I may be missing something, but, as far as I understand, the problem is that the engine and coolant are not getting hot enough. It seems that the possible causes so far suggested would be aimed at addressing over-heating, eg no circulation, pump ineffectual, air lock.  What causes lack of heat?  It seems that the thermostats that have been tried are functioning correctly, so what else is there?  If fuel is being burned, and there is no mention of a lack of performance, where is the generated heat being dissipated? tomw92, I'm also at a loss.

Mike

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1 hour ago, Troll Hunter said:

I may be missing something, but, as far as I understand, the problem is that the engine and coolant are not getting hot enough. It seems that the possible causes so far suggested would be aimed at addressing over-heating, eg no circulation, pump ineffectual, air lock.  What causes lack of heat?  It seems that the thermostats that have been tried are functioning correctly, so what else is there?  If fuel is being burned, and there is no mention of a lack of performance, where is the generated heat being dissipated? tomw92, I'm also at a loss.

Mike

Or heat being produced by the engine isn't being sufficiently transferred to the coolant...

*edit. Remember the thermal efficiency of internal combustion engine really is terrible. Most of the chemical energy in the fuel goes to making waste heat. 

Edited by monkie
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Where is it going, if not into the coolant?  You said that you had taken the temperature of the actual engine block as about 60 Deg. C.  If the heat isn't going into the coolant just about the only other places are the exhaust, so your manifold and pipe should be glowing, or into the engine oil, and I'd expect that to be seriously degraded in double quick time.  Have you taken the temperature of the sump pan after a hard drive?  If that is normal temperature you've discovered how to destroy energy, and should be in line for a Nobel prize!  Alternatively, you may have a super, and I mean SUPER, efficient engine that uses hardly any fuel.  What sort of MPG do you get?

Mike

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6 hours ago, Troll Hunter said:

Where is it going, if not into the coolant?

Where would the heat go if you ran the engine with no coolant...? I think you are over complicating this, there are no strange physics going on here. That lump of iron that is the block and head are massive heat sinks. 

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On 1/21/2021 at 11:03 AM, tomw92 said:

it's generally bit sluggish (yes, more than usual!).

If it's down on power for the usual reasons, might only be putting out 40-50hp and just not creating enough energy to heat that big lump and full width radiator. 

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Do you get a bit of pale white smoke, very easy starting and a fairly smooth engine sound even when the accelerator is on the floor?  Just wondering if the fuel injection is too retarded - it would give sluggish performance and low temperatures, plus the above.

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Hi Folks,

Sorry for the lack of update, I've been a bit tied up with work (le sigh)...

I'm yet to take the pump off and take a look, but will hopefully get round to it this week, all being well. Work is a bit crazy at the moment.

@Snagger, I get white smoke when starting, but it's fine once I'm away. If anything there's a small amount of black smoke when I'm giving it the beans. It starts just fine and sounds like any other 2.5na (LOUD!).

Cheers,

Tom

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12Js are quiet and smooth compared to Tdis!  Mild black smoke is correct on full throttle, along with a sharper but not raucous sound.

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