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300Tdi cooling issue


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I have a 300Tdi installed into a 2.5NAD engine bay, and I have always had 'concerns' about coolant. It runs the original pressed-tin header tank, and the engine is higher in the engine bay than standard so I'm not certain the header tank is high enough, or big enough for the job. I can fill the header tank right up, but the tank is empty again at the end of the next journey - presumably the water's gone out of the overflow pipe as it expands. However, opening the cap with the engine running always spits water out as you'd expect, so I presume it's full when the engine's up to temperature. I've run the engine with the header tank cap off and I can see a stream of bubbles in the coolant flow going across the tank (from the de-gas pipe) but it's not pressurising excessively and there's no oil in the water / water in the oil.

Recently, the temperature gauge has been dropping back to 70deg during a run, although the heater's still warm, so I swapped the thermostat out with a known good one. As I removed the thermostat housing... it was empty of water entirely :o so the level in the block when cold must be pretty low.

Do I just need more expansion volume or a 'higher' header tank? Thoughts / suggestions please.

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Sorry John, sound like the head gasket to me. Mine did pretty much the same, no exess pressurisation, bubbles in the coolant, coolant loss, clean oil and no oil contamination in the coolant. On the bright side it is a one day job with tea breaks and the bits are not dear. I have a torque wrench and the angle tool if you need to borrow them.

Chris

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id heard somewhere that those tests for zorst gas in the coolant dont work on deepfatfryers cause they check for the wrong gas, anyone know for sure?

most tdi headgaskets seem to go around no4 cylinder & just chuff/lose compression. id guess it'd gone towards the water jacket in this case. i know what you mean about no other symptoms, but if it has gone then do you want to wait for more damage to occur to produce those symptoms?

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I forget exactly where mine went. It was from one or both of no. 2/3 into the water jacket. It was only just leaking though.

I would imagine that the machanics at pretty much any bus garage could help with coolant testing... :) Failing that most back street garages will have the kit to test it for a few quid.

Chris

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That's it then - if Mo's works with the steel tank then mine should.

Do I just need a replacement (1,2,3 hole as applicable) head gasket and a bucket of coolant? I've got torque wrenches and sockets.

Angle guage in the post as per your PM.

Yes, you will need a head gasket and, unless you like weight lifting (looking at you I cannot imagine that to be the case! :D) some manifold gaskets too. I would reccomend new head bolts as they are stretch bolts - so in short, buy a de-coke kit which will have all the rubbers for the rocker cover and valve stem oil seals too. Check out the main stealer price for parts as some stuff (like bolts) can be cheaper there than at the motor factor - I discovered this when changing the Freelander head repeatedly. :( Oh no, the Freelander, I am all depressed now I have thought about that...

Chris

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Further to my musings on head gaskets I've done some numbers and I'll share here. Considering I want to do more tuning work on the LR in the future (especially on the turbo) I shall fit the thickest gasket. It's common practice in petrol engines to lower the compression ratio when supercharging or turbocharging to prevent knocking, and the same principle in a diesel will reduce the very highest pressures, at the slight expense of fuel consumption (when operating off-turbo).

For engines which currently have the standard 19.5:1 compression ratio with a 2-hole gasket, the following applies:

gasketthicknesses.jpg

This means that compression will be down by 6% on all cylinders, or to look at that another way, the boost can be increased by 6% so that compression energy can come from the (free) exhaust gas instead. It will have more lag and use the turbocharger more, but that shouldn't be for too long.

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This means that compression will be down by 6% on all cylinders, or to look at that another way, the boost can be increased by 6% so that compression energy can come from the (free) exhaust gas instead. It will have more lag and use the turbocharger more, but that shouldn't be for too long.

Is power directly proportional to compression ratio? In a diesel, I suspect not.

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No y'eejit, it's proportional to expansion ratio. The difference is, at a lower CR and higher boost pressure you'll only expand through the same ratio (hence poorer fuel consumption) but by working higher up the P-V curve you'll extract more energy (or the same energy with less stress on the engine) as I understand it.

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More "testing" at the weekend - I added less than half a litre of water from cold (replacing what gets pushed out by expansion?) and drove ten miles Bristol to Bath with water temp bang on 88 degrees, with a mixture of hard dual-carriageway driving and round town. Late in the journey the temperature needle dropped to 60 degrees and stayed there, and it wouldn't get any warmer on the return journey (after 5 hours stood on a frosty night).

At the end of both journeys, the header tank was full, and revving the engine produces a flow across the header tank (with a stream of small bubbles). I didn't check to see if the thermostat housing was empty again, but I suspect it was from the low indicated temperature.

I'll pull the head at Christmas but I'm erring more towards a de-gassing problem because it's not using water...

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For some interim closure on this (I know you're all losing sleep over my phantom coolant problems) I took the car for a run up the motorway last night. The gauge points here:

tempgauge.jpg

50 degrees? 60 degrees? 70 degrees? We could start a survey.

but using TroddenMasses' thermocouple and Fluke meter, the coolant in the header tank was at 80 degrees C, so I'm of the opinion that there's not too much of a problem really. I'll pull the head over Christmas anyway, but I'm increasingly leaning towards an instrumentation problem... just like last time!

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Did you use the RaceTech sender unit to go with the gauge, if not then the gauge won't read correct? The sender will screw into the hole the standard 300Tdi fits into. Thread pitch isn't exactly the same but its v close and it doesn't leak...I've got the same gauge and with the correct sender it measures the same as K type thermocouple that I had temporarily plumbed in. Others on here will vouch for the accuracy of the RaceTech gauge - far better than the original LR one!

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:huh: I did buy the correct sender, and it worked like a dream when it was new. I'll run a new wire between the gauge and sender at the weekend, see if that makes a difference. Otherwise it's a new sender I think - can anyone remember the thread that 'nearly' fits - M10x1.0?

300Tdi water temperature gauge sender unit. The bit that firs in the thermostat housing.

Thread is 1/8 NPT

Many years ago when fitting a 1600Riley engine inti a Morris 1,000 I was told the more water you have above the engine the better the cooling will be.

I ran that car woith a Mini radiator alongside the pulleys !!! A nice big [Ford Transit] header tank where the battery should be. Never had any cooling problems even on a hot day.

mike FOAK

Knickers

I can cause trouble in an empty house !!

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