620R cooling

[7 wonders of the world]

PRT stat will work but the solution is already in the car which CC choose to ignore by incorrertly plumbing the 620 in the first place - despite plumbing all previous Duratec's in correctly.

The stat can be pushed open at sustained high RPM as CC use the standard pulley size on the water pump which as pointed out previously overspeed the pump increases water pressure and lead to caviation and excess air being forced into the bottle.

Cosworth offered an oversize water pump pulley for high rpm applications or the alternative I use is a TTV undersize crank pulley as this keeps both water pump and alternator happy. The oversize pump wont fit on the 620 as space in that area is too tight.

Mark (IOM) understand your frustrations- it is a relatively straight forward cure, if I had a care local that I could work form I would sort a solution and and then sort you a kit and post it too you, fitting is very straight forward - mush mush easier than the radiator on the 420   

Mark W is now on the right lines and a good TIG welder should be easy to find as there are plenty off ally fabricators all over the country -  a few beer tokens should see the welding done no issue.

 

[CtrMint]

Thanks Neil,

Out of interest can you see any flaws in the bypass diagram I've posted.  I know it's not perfect, but surely a big improvement for road driving.  I might even be able to setup a stepper motor and drive the valve from the value the temp sensor is seeing.

[Doctor]

Oversized water pump pulley does fit the 620R - just done it. The only change needed is the longer belt - went from 6PK 1718 to 6PK 1755.

[7 wonders of the world]

Doctor thats a result  - which model pulley did you use..?

[Doctor]

kitspares.co.uk

search for Duratec

[7 wonders of the world]

your car must be an SV then...?

 

[Doctor]

It is. 

[Shropshire AR]

Igor, we would  be very interested to see if the slower rpm of the water pump effects the operating temperature at all, or is it just a fix for the possible cavitation at high rpm. 

If Caterham suggest that high internal water pressure is pushing the stat open more than it should do this larger pulley and resulting slower pump speed might help. 
 

[Doctor]

I'm not sure I necessarily agree with them on this one. The way the water pump generates the water pressure in its housing - that pressure would be pushing the cold limb of the stat shut if its spring would be weak enough. Basically there should be three inflows of fluid into the pump housing: cold limb of the stat from the rad (where 620R has a built in permanent leak), hot limb of the stat (normally bypass) and permanent flow (header tank fill +/- heater) - this one is deleted on 620R and the tank +/- heater is plugged onto the hot side of the stat where the bypass should be. All in all the problem we have is too much of a cold flow when not pinning it. I struggle to understand how and through where would pump generate the pressure high enough to open the cold limb of the stat (opens towards the block) under plodding along regime (with the cold limb bypass already built in into the 620R stat housing). 
 

Two things came together: stat having to rely on radiant heat from the block due to the lack of hot coolant bypass and system that is designed to deal with peak heat management not really considering off peak regime too much. Should probably add the third thing - a s**t water temp gauge and no oil temp gauge. 

[Mark w]

If Caterham suggest that high internal water pressure is pushing the stat open more than it should do this larger pulley and resulting slower pump speed might help. 

 

If you look at the Caterham aluminium housing you will see that the thermostat is only fixed in position on one edge . In the Plastic housing its fixed tight on both sides . 

If the flange of the thermostat is thin and flexes under pressure its conceivable that the stat in the aluminium housing bleeds round the edge on the opposite side to the single fixing point as well as through the machined cut out , even though the stat is notionally closed . 

Just a theory , ive not taken it out to look yet but if its a sloppy fit it wont help.

[7 wonders of the world]

Mark (IOM)

I would look at getting a system with a correctly functioning stat either using the OE or a PRT, a manual valve is just another thing for you to forget whilst in the throws of enjoying the mountain ! ......it adds unnecessary complexity

The water pressure can open the stat this is more a problem for engines running sustained high rpm, the 620 is not an engine you normally rev the nuts off as you would a NA engine.

I would not consider the QED option as this isolates the stat and offers no bypass feature.

 

 

[Mark w]

Ok

so after James Bs nag I will post an update .

New thermostat housing ordered ready for alteration

Bypass hose ordered 

Doctor has sourced and ordered the modified rear water outlets with the correct tappings  and outlet diameters .

A couple of alternatives for the bottle feed connection have been trialed . Neils idea seems to be the most promising so a mock up has been made in true Blue Peter style .

Neil any comments on this last bit ? It's a -8 fitting and the top entry elbow can be 90 degrees now we've moved the male fitting to face vertically .the internal diameter of this fitting is exactly the same as the internal diameter on the exit from the bottle .

ps your not commenting on my woodwork skills just the principle !!

[Mark w]

The other thing I've found out today is that the oversized pulley for the water pump will fit on my S3 despite all the plumbing in that area .

I am not going to fit one just yet because I am not sure the 620 needs it but that may be included in phase 2 of any changes .

 

[7 wonders of the world]

Mark,

That's nigh on exactly what I had in mind ! simple but effective.

Remember to get the little cut out welded up and dressed inside the housing too,

Good news on the water pump pulley too if you can safely squeeze in into and S3 without fear of interference with anything in the locality too.

 

 

[Mark w]

[Mark w]

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

[Shortshift]

Oooohhhh.....

Getting exciting!

James
 

[Doctor]

Right, local fabricators and custom build guys visited today, the first guess is that the stat housing is easily modifiable. Watch this space. 

[7 wonders of the world]

Indeed it's a very straightforward process, easy machining and you just need a decent TIG welder

[Mark w]

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 .

[Shropshire AR]

£176 each! 

[Mark w]

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 .
 

 

[Doctor]

Right, all of the bits are on one pile, the car is going in tomorrow to a local workshop - fabricators and welders. the aim is to alter the current 620 stat housing in order to close of the cold stat bypass and add the extra tube to be able to connect the header tank fill and create a permanent flow through there. Next is to fit the modified water outlet with the ability to connect the hot water bypass. 

[Shortshift]

All coming together, Igor (and Mark) - keep us posted!

James

[Mark w]

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 .......