K Series Cooling Issues

[glasgow]

even the most effective radiator in the world shouldn't be able to cool the water much below the thermostat temperature as the thermostat should shut off the flow to the radiator leaving only the bypass circuit.

The thermostat takes time to "shut off"

[revilla]

The thermostat should respond in seconds. When testing a thermostat in a pan of boiling water water it opens and closes fully in just a few seconds. I think in reality the idea is that under steady driving conditions the thermostat should reach a state of equlibrium where it is open just enough to provide the appropriate degree of cooling rather than repeatedly opening and closing, although in the Rover bypass installation it can oscillate and cause the temperature to cycle, However, I can't see any way in which the response time of the thermostat can explain how for example when driving at a steady speed on a fast road the temperature can run steadily well below thermostat temperature.

[Jonathan Kay]

However, I can't see any way in which the response time of the thermostat can explain how for example when driving at a steady speed on a fast road the temperature can run steadily well below thermostat temperature.

Quick brain dump to stimulate yours, based more on physics than knowledge of car engines, nothing excluded, common sense set to OFF:

1. The coolant is being cooled somewhere other than the radiator.
2. The thermostat doesn't stop all flow through the radiator
3. The temperature is being measured at an inappropriate place for comparison with the thermostat rating.

Jonathan

[revilla]

All good points, but:

1. So why does blanking the radiator solve the problem? That suggests the radiator is still cooling significantly. Sure heat will be lost through other places but the radiator seems to be very significant.
2. It should do when closed, other than the very small bleed through any hole drill. Very very surprised if there's enough flow here and I think we've had examples of overcooling without drilling. There's no other way back from the radiator other than through the stat and it should close fully unless faulty.
3. Yes and no. It's a funny old setup on the Rover. The thermostat is in the return line from the radiator, not the feed to it where the temperature gauge resides. When closed, it responds to the temperature of the bypass flow. As it opens it gets a blend of the two. However, the water will be at its hottest where it leaves the head and this is exactly where the gauge sender is. You would expect the water here to be no cooler and possibly quite a bit hotter than when it reaches the stat. So if this does introduce an error in the gauge reading, it would tend to read hot rather than cold (actually it is wrong to call it an error, it would be correctly reading the peak temperature of the coolant and indicating head temperature but this may be offset from thermostat temperature).

Is it possible that there are large percentage of thermostats out there that just don't close properly?

[Jonathan Kay]

Looking that way, isn't it?

But again I say that not understanding the flows... if I were designing something like this I'd want a two-way switch! Have you got a convenient schematic you could share?

Jonathan

[john milner]

What would happen if a thermostat was installed the wrong way around?

 

[revilla]

It wouldn't fit in the housing

 

[revilla]

It wouldn't fit in the housing

 

[john milner]

I have read that the size of K Series water and oil ways is of variable quality and that the metal in VVC engines is a bit better. Perhaps this leads to less problems with VVC engines and the others being inconsistent.

I would have that overcooling would in most cases be caused by a stuck or missing or wrong value thermostat. Any surplus cooling capacity of the radiator should make little difference if the thermostat works.

[Dave_P]

Ok, this is some can of worms. I have thought of blanking part of the rad to cure the over cooling but concerned about the temp increase at rest.(see origional post) I was wondering if replacing the standard fan with perhaps two 7 inch ones. More of the rad would be covered so hopefully less air passing through when fans not running. But when fan required a small increase in cooling would be achieved. Done the maths, but does not take into account fan hub sizes mounting brackets etc. Has any one run with anything other than standard fan setup. 

[gulf 1]

I have the standard cc cooling system but I have noticed when the heater is turned off the coolant temp fluctulates slightly up and down although not enough to worry about,however with the heater on the temp.is rock steady at 80C on the gauge.I have changed from an 88C thermostat to 82C with a 2mm hole drilled and fitted a Radtec radiator. The symtoms I describe also happened before changing to a lower temp stat but just at a higher temp.I am inclined to think it is just another Caterham quirck with their cooling system set up.

[AndyCam]

It is a can of worms, the variability of coolant temperature between different cars could be due to many factors.

From experience mine only exhibited this problem after a drilled stat was installed and the rad was flushed out. So at a risk of post hoc ergo propter hoc, either my rad now works better or the flow through the thermostat has an undesirable side effect, or both. I had the coolant temp drop with 88 and 82 rated stats, though the latter is less marked.

I found this article which may give a clue related to the K series in the Elise

"A common attempt to improve things is to drill one or more small holes in the original thermostat outer ring to allow a small flow through even when closed. As it works as a small extra bypass it does reduce the dynamic issue, while the thermostat will adjust to maintain the static issue as is. It also needs to be said that the drilled thermostat does increase a little the flow with the stat closed (which is good) but it also cools the bulb, keeping the thermostat closed for much longer (which is very bad)."

So maybe you can make it better but not solve the problem completely?