VX Too Cool

[gordon wilson]

I'm runnig a 2 ltr VX re-con unit supplied by Caterham with standard steel rad, the temp gauge wouldn't show more than 65/70deg and I was worried about engine wear at less than optimum temp so changed the thermostat (from local factor marked up 92deg) with no difference - still runs at 65deg. If I leave it ticking over it will eventually rise to an indicated 80deg when the fan cuts in. Is this low temp likely to be harmful? I guess the gauge/sender could just be reading 20deg low? Any remedial suggestions gratefully received.

 

Gordon

[stevefoster]

It sound like your sender or gauge is indicating low.

Mine runs at just over 80 and the fan cuts in at ~90.

 

Suspect the sender first.

[EFA]

Yep. Std stat runs at round 82 deg. Siunds like a faulty gauge or sender.

 

Easy diagnosis:

 

Swap the oil pressure and water temp gauge conmnectors around (under dash) and see if the needles still point to the same angle on scale. If they do, the water temp sender is likely faulty, if not the water temp guage is likley faulty.

 

Fat Arn

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[Chelspeed]

I agree with the diagnosis (but didn't realise the oil pressure and water temp gauges were calibrated the same).

 

But in any account don't worry about running at 70 degC water temp even if it turns out you are. Optimum water temp of 90 degC you see in road cars is an economy / emissions thing. For peak power you want to run the water temp colder because you get less charge heating before combustion. I paid a fortune for a custom made thermostat to keep my engine around 70 degC.

 

Oh and before someone points out that F1 engines run at 130 degC thats for a different reason, better fluid to air transfer from the rads and coolers. In todays aero dominated F1 packages getting coolers smaller obviously out weighs the benefits of a cooler engine.

[gordon wilson]

Steve, I think you are right, thanks for confiming your running temps.

 

Arnie, top tip - in principle, just tried hooking water temp lead to oil pressure gauge and when I turned the ignition on the needle went to the max stop...I'm off to get a new sender....

 

Chelspeed, thanks for the info/reassurance, it was relly the oil I assumed needed to get to optimum temp for best effect, but I guess cool, within limits, is no bad thing here either?

 

Thanks guys

 

Gordon

[EFA]

Graham,

ASAIK the gauge mechanisms are all the same just with different scales, so the needles should behave in the same way. This is certainly true for the VDO's that were in my car, as I had a similar problem to this a few years ago.

 

I believe the calibration (or linearity thereof) is derived from the sender.

[Andrew Russell]

Arnie

 

Is that the same for the fuel guage as well? See my earlier un responded to posting....... I have a problem and do not want to tear out the honeycombed boot floor to change the sender unit in the tank if it might just be the guage!

 

Any clues?

 

Andrew

[Coose]

Temp senders are either based on a thermcouple or thermistor, which depending on the materials used in construction determines the operating range. For example, one thermistor with an operating range of 40-110 degC will give a resitance of, say 10Kohms at 70 degC, whereas a thermistor with an operating range of 70-140 degC would have a resistance of the same 10Kohms at 100 degC. This means that the same gauge can be used, but with scales relative to the operating range of the sender, hence the ability to swap gauges to check the relative needle positions.

 

To check the fuel sender, find out from the manufacturer/supplier the max and min resistances of the sender and check this at the gauge by disconnecting it and using an AVO (or multimeter) set to ohms to test these values with a full and empty tank. Saves ripping up the floor when it could easily be the gauge at fault!

 

Coose

 

P.S. The cooler the better!

 

Edited by - Coose on 1 Apr 2002 19:14:34