Mark w

Still expensive , I had to send a 27KG WC to Germany last month and it only cost £12.30 by DPD air freight-48 hour guaranteed delivery ( Parcel Hero ) I dropped a bit of a clanger and bought the wrong thing , was pleasantly surprised how cheap it was to send it back given the size and weight . PS i can confirm that Villeroy and Boch sanitaryware is much cheaper from German outlets than it is in the UK . Now , back to OBD connectors ..........

Mark , thats not quite right , Water exits the rear of the block , and returns to the rad as you have indicated . The temperature isnt sub 82 degrees , its whatever the engine has heated it to , it flows through the rad and is returned to the block via the thermostat housing . The expansion pipe bleeds air from the system and some ( minimal ) water flows this way and is returned to the thermostat housing on the block side of the thermostat .It is the temperature of this flow which is actuating your thermostat . The heater circuit mirrors the route of the last para . The arrows on your diagram are correct for the direction of flow but your words "therefore coolant will be forced into the 16mm bypass and back towards the heater" ... are not .

Obviously using something far superior to Royal Mail first class , maybe a white gloved butler carrying them on a silver tray ?

There should be a spare connector behind the dash for shift lights , its got the correct black/white ( or is it white/black !) signal cable .I would try and find / use that rather than cut the dedicated tacho wiring .

I said I would give you the fan switching parameters , this is what I have on mine . On at 92 , off at 90 .

Mark Whilst you are thinking about thermostats think about the standard Duratec one , its double ended , when it heats up it opens to let cold water flow from the rad whilst at the same time it closes the bypass loop . Not trying to be obtuse here just want you to think and understand how the system on your 420 works .

i can't see where it states this is 82 degrees , the standard Rover ones are normally 87 or 88

https://www.dmgrs.co.uk/products/prt-thermostat-rover-75-mg-zt-1-8-k-series-pem100990 This one is 82 degrees

Mark Igors fitted a larger water pump pulley which reduces the water pump speed , this might help with any issues of the thermostat being forced open at higher revs . Ive left mine as standard at present to see if there's any difference in performance when all the other parts are similar . Don,t forget in the standard CC system on the 620 there's no volume bypass ( only the small diameter bleed to the expansion bottle ) so water has nowhere to flow when the thermostat is closed, This might cause it to be forced open.With a proper, larger diameter bypass from the rear water outlet on the block back to the pump the water can circulate through the engine without having to force a route elsewhere . Thats the main reason we ended up going for the solution we did . I will have a look at the standard CC map settings for you tomorrow and tell you what the fan switch on setting is . The standard OEM thermostat is operating against water temp on the engine side of the stat , its expecting the rad feed temp to be lower . I repeat what i said earlier , i think the remote stat solution could work but i have reservations about leaving the original stat in place . https://www.eliseparts.com/shop/engine-br-gearbox/cooling/pressure-relief-remote-thermostat-kit/ This appears to be 82 degrees

Mark Ive also just noticed that the thermostat in that bypass unit is 87 degrees , that means that it will circulate water back to the engine until it reaches quite a high temperature . The standard 620 thermostat is 82 degrees , just check you wont have a miss match with the fan switch on setting on the ecu . If you do the fan may run continuously . The remote stat idea should work but you just need to think through all the affected issues .

Hi Mark One comment on your initial post , you say that you think the OEM thermostat is being forced open by the water pump pressure causing the cold water to flow , Based on what we've found running our modified design in the other thread i don't think that's the case , the cold water flows in the OEM set up because of the big machined cut out in the housing, its akin to trying to fill a bath when you've left the plug out , the water keeps escaping . Have a look at this picture and you will see what i mean . Good luck with your alternative solution , Just have a think about what the effect of having the original thermostat left in position might have on the way the system responds , each thermostat is going to be responding to different sources , personally i think you need to remove the OEM stat if you are fitting a remote one .

Sorry , forgot this which wasn't in the box . Mark After we've run one car at Anglesey on track ( on the 10th ) just to check its ok , we have agreed to write this mod up as an easy to follow guide . All the parts bar one are available off the shelf , the modified thermostat housing is more problematic but I am not adverse to sorting out a bulk buy if there was enough interest . As a guide the cost would be £400-£500 for the thermostat housing ( starting with a new one from CC at £190 ) plus £100 for the water outlet £ 20 for the bypass hose , say £15 for water gaskets and £20 for plenum gasket . This assumes we use the chap who prototyped the design Igor and I developed to manufacture some more thermostat housings , possibly the easiest route if not the cheapest .

Kit of parts And if you think you have the skills to strip the plenum off to get access , you can fit it .

James My parts are still in a box ( 200 miles away !) when I get them I will document the changes as they are fitted on the car . Once we've got two installations up and running Including a track day thrash we could perhaps look into seeing if there's interest in a group buy . The cold running appears to have been sorted , we just need to check we don't have issues with hot running after sustained thrashing on track . We chose to go the all new parts route so that the mod was reversible , it's cost us several hundred pounds each , some of which was buying off the shelf components to see if they fitted , some was just buying in stock parts like the Caterham thermostat housing which retail at £180 each (plus the modification costs ) Maybe a quick show of hands from anyone who might be interested in doing the same ?.

Here's a few shots of the modifications .

So Igors car has been modified and the initial reports are that it warms up quickly and holds the temperature OK . Poor chap has to work this evening so cannot pick it up from the fabrication workshop until tomorow . Full report with photos to follow .......

My 981 GTS is one of just 75 manual cars . Of those only 5 were fitted with the lowered passive damper set up .I get a call about every 6 months from my dealer trying to buy it in for customers looking for one Last offer was over £40k , not bad for 6 year old car that was mid 50s new .

rubbish to fill box

Sold my C2s manual back in 2009 when i went over to the dark side and bought a 997.2GT3 . I suspect that the C2s hasnt dropped much in value since . Good luck in the search . PS Ive got a 6 cylinder GTS Boxster now ( and its a far better car )

Might be worth a read of the Additional points section .

After all this is fitted and tested we might be able to offer a modified part as a bulk buy but based on initial discussions it will be quite expensive due to the machining and angled drilling required .

new housings from Caterham ready to modify , not what you would describe as top quality welding . thankfully the welder we sourced has agreed to tidy them up .

Water outlet with bypass connection and two sensor tappings have arrived .

10th August