Temperature drops when revved - Sigma Supersport 140

[W33SVN]

Thanks Derek, I tried my OBD dongle and app, but it couldn't connect to the ECU. I do have access to another dongle, so will try that. Thank you. 

[W33SVN]

Prior to a new OBD reader arriving, I couldn't find my other. I tested coolant hose temps with my infrared thermometer. This indicated the gauge was reading correctly and the fan now does indeed kick in when the gauge reads 110 rather than the previous 85-90 degrees prior to the new sender, thermostat and fluid.

The above makes me question whether the thermostat is not indeed an 82 degree as it's part number suggests. I have now ordered another thermostat, as discussed on this forum, a CIRCOLI part no. 209590300. The original thermostat was not stamped with a temp and was shorter than my original thermostat, albeit meant to be 82 degrees.
 

I will update my findings. The increase in running temp I believe must be down to the thermostat, albeit it still seems to overcool when driven. This I will clarify tomorrow with my OBD reader and app when driving. 

[ScottR400D]

The thermostat shouldn't affect the temperature at which the fan comes in unless it's coming on immediately as the stat opens and the hot water gets to the sensor. 

[Jonathan Kay]

"The above makes me question whether the thermostat is not indeed an 82 degree as it's part number suggests, QTH576K. I have now ordered another thermostat, as discussed on this forum, a CIRCOLI part no. 209590300. The QTH576K was not stamped with a temp and was shorter than my original thermostat, albeit meant to be 82 degrees."

You could test them both in the kitchen...

Jonathan

[W33SVN]

Sorry Scott, I'm going to show mechanical ignorance here, have you any ideas why the fan would come so much later after changing the sender and thermostat? I pondered an air lock, but every hose gets hot. Gauge showing the same temp as the sender body when taken with an infrared thermometer and I'm sure I only have the singe sender under the coil pack. Unless, it's meant to come on at 110 and previously wasn't operating correctly???

[ScottR400D]

No, I have no idea. I understood that the temp is set in the ECU and is related to whatever stat should be in the car. I was thinking that the sensor was in the rad but of course it isn't so it can't be matter of the fan not coming on until the stat opens. 
 

We need someone to confirm how the fan switch temp is set and if it's fixed. 

[W33SVN]

Thanks Scott, I've assumed the rad fan was driven by the signal from the sender, just as the gauge is. It seems cars are often wired differently. 
 

[Jonathan Kay]

Have we ever found a Sigma wiring diagram with only one sender?

Jonathan

[W33SVN]

Hi Jonathan, I have looked at a build manual (2.2), but it has the hose fitted sender and no other mention of a second sender. No wiring diagram though, although I did try to Google. I'll keep looking, it's a great shout 

[150SV]

On my 150, if I disconnect the single temp sensor, the fan goes ballistic....

[W33SVN]

Thanks 150SV.

Thanks Jonathan, found a wiring diagram that confirmed one sender only.

I've just read my Owners Handbook, it states "the optimum operating water temperature for your engine is 110 degrees C" (maybe there's a lesson for me there), so clearly it wasn't reaching its proper operating temperature beforehand. Still doesn't explain why it drops so dramatically when revved, but the new running temp and fan operation temp no longer concern me. Albeit, many Sigma owners seem to see the 80-85 degrees I saw previously.

[StevehS3]

My 310R with factory radiator is rock solid at just over 80 degrees on the gauge. Winter, summer, road, track - always the same unless in standing traffic in which case it goes higher until the fan comes on. My manual says "the needle will rise from the lower (cold) mark to the middle part of the gauge, where it will remain while the engine is operating at its normal temperature." 
I think mine has only one temperature sender and the ECU controls the fan.
I think the Duratecs run hotter.

I wonder if yours has a different radiator which over-cools when the thermostat opens? 

[ScottR400D]

Both the Sigma and Duratecs have had different temp stats in at time depending on where the engine is from. 

As far as I can see the only advantage of running them hot is emissions/economy. 

[W33SVN]

Thanks Steven and Scott, I'm going to put my original temp sender back in and see what happens. 

[W33SVN]

I'm sorry to keep coming back folks. I appreciated my overcooling issue has now morphed into running considerably hotter than it did pre-coolant, thermostat and sender change. 
 

Original sender back in, just the same. Up to 110 before fan kicks in. Haven't taken out just in case I might overheat it.

I have however noticed the radiator bottom hose is only getting hot as temps approach 105ish at sender. Should the bottom hose not be very hot at a much earlier temp? 

Could I still be looking at an air lock? 

[150SV]

All my hoses are almost to hot to touch, inc heater when the stats opened.....

does sound like a possible airlock?

[DerekH]

When I fill my Sigma I run the engine with the cap off and the radiator bleed open.

When the thermostat opens the header tank level drops and the water comes out of the radiator bleed.

Close the bleed, top it up and run it up to temperature.

Done 3000 miles this year after fitting a Radtec with no issues other than it maybe runs a bit cooler by 10 degrees.

The other way of checking you have no air lock is to measure the volume of water/coolant you put in. Capacity is supposed to be 5 litres

I think I got just over 4.5 into mine as you never get the block completely drained.

DerekH

[W33SVN]

Thanks folks,

Prior to even running the car today, I raised the front end, took the radiator screw right out and the expansion bottle cap off. Upon turning the key and starting the engine, I had a pink fountain erupt from the radiator bleed hole. 
 

Was I being stupid and this was obviously going to happen, or does this also show a potential blockage from an air lock? 

[DerekH]

On a sample of one, mine only does that when the stat opens.

Derek

[ScottR400D]

#43 IME the Sigma isn't hard to bleed. Just fill with the radiator vent open. Squeeze a few pipes. Done. 

Yes, that's exactly what I'd expect if you start the engine with the vent open. Path of least resistance. 

Did you test your stats? 

[StevehS3]

As above, my Sigma with a heater was very easy to re-fill. Didn't need a second go at it. 

[W33SVN]

Thanks guys, I'm a mechanical buffoon. 
 

Just bought another thermostat and will fit this weekend. Different manufacturer and actually stamped 82 degrees.

oh yes, thermostats tested, didn't go down well in the kitchen. What's that you're cooking? Nothing. No show me, what on earth are they in the pan?

Anyway, far left original thermostat that was slow to open, failed to open fully and remained open even when temp returned to mid 70s.
 

Far right, brand new and not fitted, started opening at 82, fully open by 88 and shut again at 82. 
 

Middle was another that's been fitted and was again slow to open, failed to open fully and slow to close.

However, all did work to a degree.

 

[W33SVN]

Thanks Steve,

I've swapped a thermostat before with no issues at all, never reached anywhere near 110 in the past.

[ScottR400D]

#47 looks like only the new one is working properly so fingers crossed. 

[StevehS3]

Did you have any luck with the ODB reader? Did it connect to your ECU?