What temperature stat ??

[Mark w]

So the percieved wisdom is to change the Thermostat in a K to one that operates at lower temperature to protect the head.As i understand it the standard one begins to open at 85 degrees,there is an 82 degrees available and also a 74.

My engine is a 200 hp R400 with a tripple pass rad mainly user on the road but with the odd excursion onto the track.Cold weather like we had last week sees the Stack showing 78 to 80 degres on the motorway (I have never understood why this is if the stat doesnt open till 85 but i guess it is because some coolant bleeds into the engine through the stat even when closed),rising to high 80s or even low 90s in heavy traffic.

I am keen to stabalise the temp as much as possible,if i change the stat ,what should i go for.?Two options so ,no doubt,i will get two polarised replies!.The 74 seems quite a step down but 85 to 82 doesnt seem much different

Pros and cons of each ??

For those that run a 74 degree stat what temperature fluctuations do you see , i.e. does the engine run lower temps in normal driving but still creep up into the high 80s in traffic.

[Myles]

I guess it is because some coolant bleeds into the engine through the stat even when closed),

 

This is indeed true for most stats these days - they have small bypass-holes drilled in them. Some people seem to think this is a good idea to help bleed the coolant system - but the real reason/benefit is to allow some flow through the radiator at all times.

 

Personally, I've been running 78 IIRC for quite a while in my standard 1.6k - this does keep it pretty stable (even on the track) - but, yes, of course it will still rise 'way above' this in traffic - an open-stat is an open-stat...

 

The scare stories about thermal shock and creating large temperature gradients across the head (leading to HGF) when using lower-temp stats are mainly (IMHO) the result of such installations in Elises etc. where there is such a distance between the rad and the stat/engine (allowing the coolant to drop more significantly in temp). The short hose-runs in the 7 should allow the system to reach a more stable equilibrium.

 

IN discussing this in the last few days, someone pointed out to me that the outlet coolant temp from the head is not fixed - so dropping the inlet temp (via a lower-temp stat) will not necessarily cause a large gradient in itself.

 

I know a number of tweaked VHPDs (200ish bhp) have been running 74s or thereabouts without any trouble - I'd be tempted to go for it in your case (I'll be putting one in to my new engine).

 

 

 

Project Scope-Creep is underway...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

[Shaun_E]

I have never been entirely convinced that lower temperature 'stats can be of any great benefit. In theory the temperature at which the 'stat opens is the steady state temperature the engine coolant runs at - if the engine coolant temp exceeds the 'stat setting the 'stat opens and reduces the temperature until it closes again. The average temperature of coolant in the engine is therfore close to the 'stat opening temperature. If an engine is designed to work at an average coolant temperature of 85 degrees then what benefit will be gained by trying to run it 10 degrees cooler? The important thing is that a radiator is sized to dump excess heat from the engine and in fact if you run at a lower coolant temperature then the temperature difference between coolant and incoming air will be less and therefore heat dumped more slowly. The only possible advantage I can see is that in extreme conditions (e.g. track or traffic) the 'stat will open earlier and therefore start to dump heat sooner - the smaller temperature differential could negate any benefit from this but someone would need to do the detail maths to be sure.

I await a better informed view 😬 It's certainly an interesting debate but as you say it might just be "perceived wisdom".

 

Yellow SL #32

For Sale: wet sump, ali bellhousing, chrome headlights, sill protectors

Wanted: Black headlights, blank carbon dash

[Myles]

The only possible advantage I can see is that in extreme conditions (e.g. track or traffic) the 'stat will open earlier and therefore start to dump heat sooner...

 

That'd be part of it. As I said before, once a stat is fully-open, it doesn't matter what temp it started to open at (assuming we're talking lower full-open rating temps than standard). If you are stuck in traffic, or caning the engine on track, your final temperature will be dictated by the cooling properties of the rad - the 'stat will be irrelevant.

 

However, in less arduous conditions (a bit of sluggish traffic, a reasonably high-spirited blat), a lower temp 'stat could help the engine run a bit cooler or at least allow the coolant to blend more smoothly.

 

I'm not sure if the analogy is at all helpful - but I have the image of soft-cut and hard-cut rev limiters in my mind.

 

 

 

 

Project Scope-Creep is underway...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

[inspector71]

My standard 150Bhp VVC engine had a 92 degree temperature stat fitted to it, One problem i found with it (and it was only by accident that i did find this) was that after i had turned off the engine the following 5 minutes the temperature would creep up to around 100 degrees, sometimes even higher.

I fitted an 82 degree one (about £6) and since, the temperature has never gone above 90/92 after switch off.

I'm not a mechanical engineer, but it seems to me to be a good idea to keep the water temp from creeping up to 100+ temperatures. Would be good to get an experts opinion on this...

regards

peter h