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StevehS3
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Just to satisfy my curiosity, why would a car run cool when fitted with a thermostat to control the temperature by varying the flow between the bypass and radiator? I hear this all the time and never understand it.

 

CtrMint
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Covered it up this afternoon with some thin flexible plastic wrapped in electrical tape, it was running between 95c and 75c depending what I was doing.  ~75c at 80mph over the Mountain, it was baltic up there.  Through the slower villages it sat mostly at 85c.  From Ramsey to Ballacraine it seemed pretty normal in terms of temps.

Neil as for giving it the beans, its been driven up to 5k, but I don't have the confidence in lower gears its so rapid, then in higher gears its a bit too quick for the public road this time of year.  Plus I'm nervous of the ZZRs in the cold.

 

Caterham 420R S3 Lotus Toxic Green,  Caterham 620R S3 Exocet Red. Blog: https://www.caterham7diaries.com
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It shouldn't in a correctly designed and functioning system, especially in a modern set up.

Mark w
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"Just to satisfy my curiosity, why would a car run cool when fitted with a thermostat to control the temperature by varying the flow between the bypass and radiator? I hear this all the time and never understand it."
 

I think it's because the thermostat has a bypass ( look at the groove in the housing picture ) which feeds cold water through even when  it's not needed plus the radiator is oversized to cover peak load so the temperature drop is too extreme in low ambient temperatures in relation to the demand .

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The bypass feeds HOT water and allows the stat to respond in a more timely manner being fed in th case of the Duratec via a 19mm hose direct form the water outlet behind No 4.

Once the hot water being fed over the stat reach the critical temperature the stat opens allowing cool water from the rad bottom hose to flow into the engine and hence as the radiator circuit is now open hot water to flow to the radiator from the same outlet albeit via a full size hose.

It then shuttles back and forth being moderated by hot bypass and cooler radiator return.

NB as the stat opens it closes off the bypass circuit, which is only reopens as the stat is cooled and closes again.

Whilst there are packaging limitations on the 620 but this is no excuse for a poorly functioning cooling circuit, bearing in mind the DS runs circa 7Ltrs of oil via a full flow oil cooler but again this runs with no oil stat - the poor engine will never reach a reliable operating temperature unless many horses are being unleashed, running the risk of dropping back into the realms of warm up fueling and therefore and washing the bores.

 

 

Mark w
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Re#16 

Theres NO hot bypass / return feed into the stat on a 620 

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Are you sure theres no bypass as this goes into the metal pipe pressed into the block itself adjacent to to the stat housing, the hose that normally fits onto the stat (absent on the photo above) is the heater / expansion bottle return.

Mark w
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OK We may be debating terminology here .

Theres a FILL pipe connected to that spigot that comes from the expansion bottle .The expansion bottle just has mini air bleed pipe serving it ( connects off the top of the return water rail ) . Whilst there will be some flow via this route it will probably be minimal .

When you said bypass pipe i understood that to mean a full flow return pipe from the back of the block direct to the stat housing .

Heres a picture of a 620 in build .

And one stripped to have the modified supply pipe fitted to enable a stat to be fitted .( old supply pipe still in place ) 

Mark w
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" bearing in mind the DS runs circa 7Ltrs of oil via a full flow oil cooler but again this runs with no oil stat - the poor engine will never reach a reliable operating temperature unless many horses are being unleashed, running the risk of dropping back into the realms of warm up fueling and therefore and washing the bores."

Good points made here , some tin foil round the oil cooler can reduce overcooling the oil .

Ive got an unlocked ECU on my car and have adjusted the cold start ,over fueling , cut off point to a lower setting so that it doesnt do this . It doesnt seem to have any adverse effects on running .

 

Jonathan Kay
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Does anyone have a cooling system diagram for the 620, please?

Thanks

Jonathan