620 Cooling - Radiator Bypass Loop

[ScottR400D]

Are you sure that’s not the readings being taken from different places? (Though 15deg seems quite a difference!)

My gauge reads around 80 and checking with a pyrometer at various places under bonnet it’s not too far off; I appreciate that’s not as accurate as reading the ECU (then again, how accurate is that?) but it all seems ‘about’ right. 

I wonder if you have the wrong resistance sender to the gauge? 

[CtrMint]

I've found the gauge in the 420 to be spot on, and the 620 has only a slight misalignment of a few %.   Assuming the ECU value is correct.

[Mark w]

To answer the queries above , both senders are in the same place , it's not the senders it's the gauge .

Swapped it with Igor's this morning and the problem travelled with the gauge . Seems there's two specs with slightly different part no's, the one ending in C is the more accurate .

Our modified bypass system worked fine on track . Going to modify the second car now .

 

[Shropshire AR]

Spot temperature checks are fine but it still doesn't get away from the alarming indicated 30C swing of temperature depending on how much air is flowing through the radiator. The thermostat does not seem to act fast or effectively enough to stabilise the temperature at the stat's rating. Could this be to do with the pressure in the system pushing the thermostat open too much. This would probably be the reasoning why the housing has such a large bypass cut out to try and minimise the pressure effect on the stat.

[CtrMint]

That's what Caterham told me, they added the cut out to ease the pressure.  

[Doctor]

Guys, we are turning in the circle here. The reason there was a pressure build up pushing the stat opened (possibly as the build in bypass flow was huge) was that Caterham hasn't built any permanent circuit in (one that would flow irrespective of what the stat is doing) which is usually through the heater and the header tank. Caterham decided to incorporate the permanent circuit into the cold return from the rad to the stat, that is why the car overcools under the regime of low -ish heat generation - the flow through the rad is out of control of the stat. Our modification eliminates all of this - we mimicked the intended flows through Duratec stat - permanent flow bypassing the stat is now coming from the header tank, bypass hose from the head water outlet goes to the hot side of the stat and the rad cold return goes to the cold side of the stat. It works, the end. 
 

Yesterday at Anglesey the car performed beautifully - set off at five in the morning (relatively chilly) and traveling westwards on the motorway doing 70-80 mph at 6th gear the water temp (my gauge seems to be quite accurate when checked against the Easymap ECU reading) was sat at 70'C. Slower traffic (40mph) the temp comes to 80'C. On the racetrack abusing it for 20min the temps stayed below 100'C. The crucial point here - we need to start measuring the engine oil temp. I'm in the process of sorting that out. Very happy with everything so far. 

[CtrMint]

Went out last night just before it got dark, drove the TT course anticlockwise, stuck something over half the temp gauge so I could only see the needle over 90, though I intentionally let it get some heat into it by driving slow to the filling station etc.  Had a blast, really enjoyed the quiet roads, it was still 20c, t-shirt, shorts on and aeroscreen driving quickly through the derestricted areas was refreshing and an excellent way to cool down from the days heat.  The grunt up the hill from the Creg to Kates, was staggering, well north of 100mph.  Thought it post something positive, since it was positive. 

[Mark w]

[John Vine]

The grunt up the hill from the Creg to Kates, was staggering, well north of 100mph. 

I recall doing that some years ago on a Triumph-Norton (at a much lower speed!), heading from Douglas to Ramsey to signal for a friend racing a G50 in the MGP.

Pleased to hear the positive news.

JV

[Doctor]

Well done Mark, that's the spirit!! My green fatty did nearly 150mph at 5th gear down the back straight on Coastal circuit. The Marshall on top of the hill felt a bit uneasy as I was coming at him. An excellent day out and the car behaved. 

[Shortshift]

"My green fatty did nearly 150mph at 5th gear down the back straight on Coastal circuit"

Blimey!  Err - according to a calibrated speedo I assume??!! 

James

[Mark w]

Blimey!  Err - according to a calibrated speedo I assume??!!   [Nerd]

I told him not to use those 10 inch wheels !

[Doctor]

Nope, just the crap one on the dash. 

It felt plenty fast enough. 

[Doctor]

Funny you should say that Mark, when it was dry, I havent seen you anywhere near.