Temp sending unit 3.9L vs 300TDI - different range? - Defender Source
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  #1  
Old September 21st, 2010, 02:28 AM
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Jason Herring
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Temp sending unit 3.9L vs 300TDI - different range?

I fired up my 300TDI in it's new home (my engine bay, replacing a 3.9L) this past weekend and it ran good, good oil pressure etc, but the temp seemed to run warm quickly (beyond mid range on the gauge), so I turned it off and started troubleshooting the cooling system.

A day later I fired it up again and noticed the temp gauge showed temperature shortly after starting - I think it's unlikely it could heat it enough to pull it off cold in 30 seconds.

Now, the connector is definitely different from my 3.9L (bullet on the 300TDI, spade on the 3.9L), so maybe the sender is a different ohm range? Do I need to change sending units?
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  #2  
Old September 21st, 2010, 06:15 AM
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Gren Thomas
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Hi Jason yes you need a 300tdi sender unit

Regards
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  #3  
Old September 23rd, 2010, 10:25 AM
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Jason Herring
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I already have a 300TDI sending unit and it doesn't work with my gauge. So... I have a 300TDI in a former V8 D90, and the 300TDI sending unit which came with the motor seems to be the wrong scale for the V8 gauge. So, I think that maybe either I need a V8 range sending unit but in the thread size of the 300TDI, or I need a gauge with the 300TDI sending unit's range.

Or replace both w/ new VDO.

What is the thread size on the coolant temp gauge on the 300TDI? And what is the range of the sending unit?

The V8 sending unit is too large a thread size to fit in the 300TDI coolant temp sensor location.
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  #4  
Old September 23rd, 2010, 12:44 PM
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one solution would be to put in the correct 300tdi defender gauge. a better solution would be the vdo or other aftermarket gauge with matched sender that provides a more accurate reading and most likely superior nighttime illumination.

the port for the 300tdi water temp sender is 1/8" NPT, (1/8"-27)

Quote:
Originally Posted by jaherring View Post
I already have a 300TDI sending unit and it doesn't work with my gauge. So... I have a 300TDI in a former V8 D90, and the 300TDI sending unit which came with the motor seems to be the wrong scale for the V8 gauge. So, I think that maybe either I need a V8 range sending unit but in the thread size of the 300TDI, or I need a gauge with the 300TDI sending unit's range.

Or replace both w/ new VDO.

What is the thread size on the coolant temp gauge on the 300TDI? And what is the range of the sending unit?

The V8 sending unit is too large a thread size to fit in the 300TDI coolant temp sensor location.
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  #5  
Old September 23rd, 2010, 10:01 PM
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Jason Herring
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Thanks!
If I go for a new gauge I'll want to change them all...which maybe is what I'll do.
Thanks again.
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  #6  
Old September 24th, 2010, 08:01 AM
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Hi Jason, i suspect you havent had much opportunity to test your swap but I'd love an update or two. I'd like to do the same thing once my petrol needs attn (now I have 78k on the clock).
What transmission did you go with? May I ask the rough $$ on the swap?

Cheers,

Eddie
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  #7  
Old September 24th, 2010, 08:58 AM
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Quote:
Originally Posted by jaherring View Post
I already have a 300TDI sending unit and it doesn't work with my gauge. So... I have a 300TDI in a former V8 D90, and the 300TDI sending unit which came with the motor seems to be the wrong scale for the V8 gauge. So, I think that maybe either I need a V8 range sending unit but in the thread size of the 300TDI, or I need a gauge with the 300TDI sending unit's range.

Or replace both w/ new VDO.

What is the thread size on the coolant temp gauge on the 300TDI? And what is the range of the sending unit?

The V8 sending unit is too large a thread size to fit in the 300TDI coolant temp sensor location.
why not get a real gauge and ditch that stocker crap?
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  #8  
Old September 26th, 2010, 03:11 PM
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Jason Herring
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Because if I swap gauges I'll want to do them all - incl speedo etc - and I will want to go 'all in' which means some ciustom stuff since VDO doesn't make the style I want in the LR stock sizes... I'll also want to add boost and probably EGT for the diesel & that then requires the 'Defender dash' center console.... it's suddenly a $1200 job :-S

Quote:
Originally Posted by rover4x4 View Post
why not get a real gauge and ditch that stocker crap?
------ Follow up post added September 26th, 2010 12:17 PM ------

I haven't really driven it much as I don't have exhaust on it yet (though amazingly it's not really so noisy with the turbo quieting it down) and I also need to make a few little brackets & things. I have only gone around the block once so far...

I kept the R380 from the V8 - I have a Disco xfer case which helps the overall gear ratios a bit but 1st is still pretty darn low and I think starting in 2nd will not be a problem...

There is a clutch/pressure plate/throwout bearing set which allows you to use the V8 R380 and 300TDI bell housing as-is without changing the input shaft - very glad I found that.

The cost? Hmmm, not sure. I'm probably around $5500-$6K by now with things here and there - the miscellaneous stuff adds up.

I'm going to tinker with it a bit today - clean up the underhood wiring and make a bracket or two.

Quote:
Originally Posted by TxEddie1111 View Post
Hi Jason, i suspect you havent had much opportunity to test your swap but I'd love an update or two. I'd like to do the same thing once my petrol needs attn (now I have 78k on the clock).
What transmission did you go with? May I ask the rough $$ on the swap?

Cheers,

Eddie
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  #9  
Old October 4th, 2010, 08:22 PM
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Jason Herring
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FWIW a standard VDO temp sender 1/8" seems to work perfectly in the 300TDI with the factory gauge.
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