OIl versus Water temp

[skydragon]

1.6K ex-supergrad car, with a Caterham temp gauge, wired via a 2 way switch to the water temp sender and the oil temp sender in the Apollo.

 

On the road, the water never gets above 80 when moving, and often is nearer 60. The car has a thermostat fitted (don't know what temp rating). On a trackday at the weekend, the water temp never went above 80-85 despite some heavy work.

 

Question - is 60 - 70 deg ok as a 'normal' operating water temp for a K-series or a bit too cool ? If so, what is the end effect of running a K-series a bit too cool?

 

Oil temp wise, in general use it's around 60, on a longer run about 80 and on the trackday went up to around 90-95 max. That sounds about right doesn't it?

 

(I haven't checked the calibration of either temp sender so I guess these figures could be eronous ? I should really check them)

[skydragon]

(I haven't checked the calibration of either temp sender so I guess these figures could be eronous ? I should really check them)

 

I've just ordered a cheapo infra red thermometer from ebay, so I can hopefully check the sensor temps and see if that correlates with the gauge readings.

[skydragon]

Ok, I ran the car up today, checking the temps with a infra red thermometer.

 

Monitoring the rubber skin of the water bypass hose round the back of the engine, the thermostat opened at around 72 deg C which I guess is about right. I know monitoring the water temp via the outside surface of the pipe won't be exact, but it should be fairly close.

 

My water temp gauge is reading approx 5 - 10 deg C too low, which is Ok as long as I know this is the case, as a reference point

 

The radiator fan however came on at around 76 - 78 deg C water temp (monitored at the bypass hose), which seems to be way too low. The radstat body is marked 87-92 which I'm guessing means it (should) close at 92 deg C truning the rad fan on and open again at 87 deg C turning the rad fan off.

 

With the fan kicking in at around 76deg C the car never got above 80 deg C water temp.

 

I guess I need to replace the fanstat in the top of the ally radiator with a new radstat -this radstat from Caterham here ?? Any tips on fitting? How tight does it need to be tightened up?

 

The oil temp reading on the switchable gauge seemed to be fairly accurate, so I'm happy with that.

[MarchHare2008]

Are you sure it has a thermostat fitted? Not sure about grads but roadsport regs require the thermostat to be removed for the race series.

[skydragon]

Are you sure it has a thermostat fitted? Not sure about grads but roadsport regs require the thermostat to be removed for the race series

 

Originaly I presumed it hadn't a thermostat fitted, but on testing the radiator and botoom retun hose stay cold until approx 72 deg C at which point they suddenlt get warm - I'm guessing this must mean a thermostat is fitted?

[Mick Day]

A few things? The rubber skin of the water bypass hose will insulate readings maybe as much as 10 deg C.

 

To get a more accurate reading of water temperature do the reading directly where the top hose goes into the rad. Measure on the metal. So with your readings you're probably in the ballpark.

 

To check whether your car has a themostat put your hand on the top of the rad & start the car from cold. Does this stay cold whilst the bypass hose gets hot? If so you have a thermostat. If it gets hot at the same time as the bypass hose then you don't.

 

Most of us have 82 deg C thermostats & yes the fan thermo switch is about 87-92 deg C, however they are not that precise. A 5 to 10 deg inaccuracy in the temp gauge doesn't surprise me.

[skydragon]

A few things? The rubber skin of the water bypass hose will insulate readings maybe as much as 10 deg C.

 

To get a more accurate reading of water temperature do the reading directly where the top hose goes into the rad. Measure on the metal. So with your readings you're probably in the ballpark.

---

 

I couldn't, an infra-red thermometer won't work on the shiny metal of the radiator, only on dull surfaces. I'll try putting some thin tape on the radiator top and measuring off that. I'll repost the readings in due course

 

To check whether your car has a themostat put your hand on the top of the rad & start the car from cold. Does this stay cold whilst the bypass hose gets hot? If so you have a thermostat. If it gets hot at the same time as the bypass hose then you don't.

The rad and bottom hose stay cold whilst the bypass hose gets hot, so there is a thermostat fitted.

 

Now we've established there is a thermostat fitted. The question now is why does the fan kick in when the indicated water temp is well below 80 deg C. Either the water temp gauge/sensor is reading over 15-20 degC too low (quite possible) or the fanstat is switching in at too low a temp.

 

[skydragon]

I tried measuring the radiator temp again, but this time used a piece of thin black electrical tape stuck to the top of the radiator to act as a target (the instructions for the infra-red thermometer suggest doing this when a shiny metallic surface is being measured).

 

This time the radiator temperature was approx 90 deg C when the fanstat came on, so that is correct/fine.

 

This means that the only issue in fact is the water temp gauge which is totally inaccurate and didn't go above 75ish deg C at any point during the test. Since the oil temp reading seems to be OK, the gauge itself is probably ok and the problem should be sorted with a new water temp sender unit.

 

This can wait until I next have to drain/fill the cooling system at which point I'll probably fit silicone hoses as well as a new temp sender unit.

 

Thanks for your help and saving me from believing the bypass hose surface is a good place to read coolant temp from..

[Mick Day]

If the gauge works in a linear fashion don't bother changing the sender. Your new sender may have the same "fault". The temperature gauges/senders can read 5 to 10 deg C out.