Temp in a V8

[iomlt]

Having searched the forum and came across this old thread ( http://forums.lr4x4.com/index.php?showtopic=51698 ) i am looking into adding a line trimmer variable resistor because i have installed a 3.9l into my 90 what was a 200tdi and now the clock is reading high,

My question is

There are so many and so many different ohms ratings,

In the link i have added above the results read below

This is the result.. (sensor value in ohms)

Temp....TD5.....3.9....3.9(2)

10......3900...1198

20......2700....810

30......1810....543

40......1213....360

50.......877....254....230

60.......636....173....184

70.......454....118....128

80.......336.....84....89

85.......298.....76....72

90.......252.....63....60

95.......224.....56....50

100......190.....50....30

Sowhat rating resistor would i need? 2k, 5k, 10k, 50k, 100, 300k, 500k, ?? i'm guessing a 2k? would this sound about right?

thank you in advance

[zardos]

Given those readings which was for a TD5 gauge (ECU controlled) I don't think you can match it with a trim resistor as the two sets of readings are not linear

e.g. adding 2000 Ohms when at water actual water temp of 20C the numbers are 810+2000 = 2810 which is close to the TD5 20C

but at 100C actual water temp the numbers are 50+2000 = 2050 which is some where between 20C and 30C (more towards the 30C at a rough estimate of 27C)

But your 200tdi gauge is probably not the same as the TD5 gauge

You would need the values for the 200tdi temp sender to work out if they were linear and what the value of the trim resistor would be if they were linear.

The easiest way is to get a gauge to match the V8 sender (my 3.9l V8 in a 200tdi) has the correct gauge.

[iomlt]

Hello Zardos,

The readings given were from this forum for yes a TD5 and two 3.9 senders,

In my other transplant 3.9 V8 90 (which is V8 from new 1985 3.5) i had to change the dial to a 50th anniversairy gauage to make it sit in the middle, In this one i want to keep an orignal dial because of the looks and i think the resister will be the easiest way as long as i can work out roughly which one i need.

How have you made yours work? are you running a 82 or 88 thermostat? what sender and gauage are you using please?

Regards

[zardos]

How have you made yours work? are you running a 82 or 88 thermostat? what sender and gauage are you using please?

Regards

Unfortunately it was done by a previous owner, so I don't know the thermostat value or any part numbers of the gauge.

I assume that you want to keep the 200 tdi gauage?

You will need to find or measure the resistance of the 200tdi sensor to see if it linear to the v8 sensor.

If it is then you can use a trim resistor.

Another option is you could probably get a water sensor adaptor (some like this in ebay) to fit in to your heater circuit house.

And then you could put the right sensor in for your gauge.

[iomlt]

I'm runing a Efi, not the carb version, so maybe you have a different sender? i know the senders arent interchangable do to thread ???

so my options are new gauage and maxing sender? or to find a way round it.

yes i'd like to keep the factory dial, i'll have to get measuring a 200tdi and go from there.

[mickeyw]

I went through this saga when I fitted a 3.9 Serp V8 into my 90. Now my 90 was a V8 from day 1, but the old style (5/8") sender (fitted to all multi-vee belted engines, 3.9 included) is electrically different to the 10mm dia one in the later engine.

Things I learned:

Adding a resistor only moves the reading. I added R to get temp gauge correct at normal operating temp, only to find it never actually registered hot when the engine was cooking. So the reading was offset, but not in proportion. Basically the two senders change in resistance by a different amount when moving from cold to hot.

A 300Tdi sender is the same thread as the serp engine. Therefore a 300Tdi dash gauge would work correctly. The standard V8 'stat is an 88 degree unit, and AFAIK the Tdi operating temp is the same.

Now you have mentioned using a Td5 gauge. Is this because of the styling, or because it was just another gauge to try?

If you have a multi-vee 3.9 then I think the 200tdi gauge, or even the 2.5 or 3.5 petrol gauges will read correct with the larger type V8 sender.

If you have a serp 3.9, then try the 300 bits as mentioned above. If you want the Td5 styling, I can recommend the VDO Cockpit Vision range of gauges being near identical with a flat faced bezel. I bought mine from Merlin Motorsport with the correct threaded sender.

[iomlt]

to save confusion i'll explain

number 1

This is a 1985 genuine V8 CSW, I put in a Multi-vee belt 3.9 from a 1991 RRC. the original clock read high (just touching the red on operating temperature, I through in a TD5 style 50th anniversary clock and it read perfectly, (half way) But really i need to replace all the other clocks now to make it look "matching"

Number 2

Still in the build, 1993/4 200tdi, again I put in another Multi-vee belt 3.9 from a 1992 rrc, again clock reads high (just in the red) at operating temp, i have x switch for leccy fan and that comes on and goes off and gauge sits firmly in the red.

The only real reason i don’t want to put another 50th anni clock in the tray back is A because of the looks but if i have too then i will but surely there is away round it. I will play with other sensors tonight and see if i can come up with something as we have plenty of defender variants cars around to try, I was just trying to save time.

AL

[FridgeFreezer]

Aren't the gauges made by VDO? Must be some VDO specs somewhere for the gauges & senders that you can have a ponder over, even if you have to tap a hole for a different sender.

[iomlt]

As temperature accurancy is pretty important when off roading especially with eleccy fans etc, i have decided to by a new gauage and matchuing sender, that way i know exactly whats going on rather than the vage reading of a lr gauge,

I will have a quick play and see if there is a matching sensor / gauage tonight but i will be fitting one of these with correct sender http://www.merlinmotorsport.co.uk/p6142/VDO-WATER-TEMPERATURE-GAUGE/product_info.html

thank you

[zim]

In answer to your thermostat question, i run a 72 (or is it 74??) degree stat. With a couple 4mm holes drilled in it. My engine (cam'd 4.2) sits between 85 - 88 occassionally up to 90, being controlled by the fan(s). Only used offroad.

G

[iomlt]

In answer to your thermostat question, i run a 72 (or is it 74??) degree stat. With a couple 4mm holes drilled in it. My engine (cam'd 4.2) sits between 85 - 88 occassionally up to 90, being controlled by the fan(s). Only used offroad.

G

I reckon if i used a lower thermostat like that my dial would read better, but i use a genuine 88 thermostat.....

[zim]

The thermostat has no effect on your gauge reading. It just opens to let water through your rad when it reaches X degrees.

[iomlt]

hello, your thermostat controls the temp of the engine correct? and your temp gauage takes a reading of your engine correct? so if you have a lower temp thermostate or a higher one for that matter thus changing the temperature of your engine surely this will have a knock on affect of your gauge??????

[zim]

hello, your thermostat controls the temp of the engine correct? and your temp gauage takes a reading of your engine correct? so if you have a lower temp thermostate or a higher one for that matter thus changing the temperature of your engine surely this will have a knock on affect of your gauge??????

But...if your gauge is wrong at 90 degrees, it is also wrong at 85 degrees and also wrong at 80 degrees. So running temperature has no effect on your gauge.

Secondly - a thermostat doesn't depict the temperature your engine runs at. It decides whether you have water circulate through the radiator or not. Or better put, once up to temperature it *should* be the minimum temp possible.

Your radiator will probably only cool it when the fan is running - thus your engine will run at the temperature your fans are set to. If your engine is working hard it'll run at hotter than the stat & fan temp.

You could possibly get around this by having fans constantly on or driving on a road at a decent speed (assuming you get air flow through the rad) - but your motor looks like an offroader.

G

Edit : I'm hope i don't come across like i'm looking for an arguement . I think you've made the right choice getting a new gauge and matching sender. Water temp and oil pressure are your engines lifeline I also have gear and engine oil temps.

[iomlt]

i did alittle to be honest, so i do appolagise,

but i have found in the past that using a lower or higher temp thermostat does make a difference to where the needle sits in the gauge regardless of the gauge being right or wrong, i have always changed a thermostat first if i have ever had coolant issues as its cheaper than a pump and or gauge... (presuming you have airflow, be it fan or forced air driving)

Do agree with engine temp and pressure, but i'm a firm believer if you can keep your water temp correct then you dont need to worry about oil temp so much.

[mickeyw]

hello, your thermostat controls the temp of the engine correct?

Not entirely. It will restrict coolant circulation to reduce warm up time. Once the stat is fully open it's down to the radiator and airflow through it to control engine temperature. So the stat can be fully open and you can be chonking around off road, but without airflow the engine will get hotter and hotter (V8s are good at that).

If you're trundling along downhill at 50 mph on a cold day, and the engine isn't working very hard, there's a chance the rad temp will drop below the stat temp, and it will begin to close restrict coolant flow and hence maintain engine temperature.

The new matched guage and sender is the easiest way to ensure accurate temperature readings. If you are inclined/have the time, you should also be able to match up the right LR parts for it to work right