K-Series cooling ... or overcooling?

[SLR No.77]

Whilst you were all enjoying the sunshine on the Fish & Chip Run at the weekend I was battling the elements travelling to and from Spa, pretty well five solid days of rain. Due to the distances involved I filled up maybe 4 or 5 times, on each occasion at around 160-170 miles, but on returning to the UK and the high temperature we experienced on Sunday I'm blasting up the motorway and getting 200 miles from a fill, the difference was chalk and cheese.

Very noticeable is that my car regularly struggles to get up to temperature and in colder conditions as at the weekend it might get barely above 70 C, sometimes dropping nearer to 60 C if I have the heater on. Then on Sunday, no heater needed, and in the hot weather it's running at a rock solid 82 C, exactly as per the thermostat that's fitted, rising a little in standing traffic but being controlled nicely by the rad fan as expected. Both the gauge and ECU temp senders are located in a small submarine type tube just upstream of the heater, so no influence from the manifold nor the heater, the temperature is as the coolant comes directly from the engine around the bypass circuit and I expect the (Stack) gauge is quite accurate.

The engine temperature is in fact very stable, other than a slight drop with the heater running it will remain consistent through a day's driving. What isn't consistent is day to day and it's clearly affected by the outside temperature. I'm guessing at this point that when not up to the full temperature the engine is over-fuelling hence the poorer economy/range on colder days.

Any thoughts on where to go with this? The car has a standard setup K-Series cooling circuit, thermostat where it should be, small hole in the stat, big rad as per the SLR.

Could it be that the hole in the stat is too large?

Would the PRRT setup or a top hose stat give a more consistent temperature in different atmospheric conditions?

I reiterate that the engine temperature is stable, there's absolutely no issues with bleeding the system, it's just not consistent and is influence too much by the weather.

Stu.

[Toby S]

Sounds like the thermostat is jammed open - I had the same sort of readings on my supersport when I first bought it and found on investigation that the thermostat had been removed completely so it was a fully open system all the time - a sticky thermostat would have the same result

[Jonathan Kay]

Could be that the hole is too large. Could be that the thermostat isn't closing.

Overcooling is increasingly being reported on K series Sevens. And a radiator blind might be the best solution... and is an easy experiment.

...

But I don't understand the big effect on fuel consumption.

Jonathan

[7 wonders of the world]

Radiator blinds are fine for Series 1 Land Rover but have no place on modern vehicles. 

The low coolant temp can put the engine into the later stages of warm up therefore you suffer increased fuel consumption. 

When I ran a K the PRRT install worked perfectly

Edited May 25 by 7 wonders of the world

[SLR No.77]

Correct Neil, I also believe a radiator blind has no place on a modern vehicle.

I’ve managed to source the bits to switch to a PRRT setup so I’ll give that a go and report back.

Stu.

[Miker7]

I fitted the 82 degree stat this winter - because that seemed the general wisdom. I don't drive like I've stolen it. When it was 10 to 15 degrees outside my temperature seemed 'cold' but I've learned the gauge displays 10 ish degrees colder than the ECU sensor. that difference would put it more like 80 degrees.

How are you measuring temperature & is their any other difference to rule out eg faster speeds abroad?

[SM25T]

3mm hole in stat plate won't overcool, but will allow air bubbles through

[aerobod - near CYYC]

 

1 hour ago, SLR No.77 said:

Correct Neil, I also believe a radiator blind has no place on a modern vehicle.

I’ve managed to source the bits to switch to a PRRT setup so I’ll give that a go and report back.

Stu.

Radiator blinds and becoming more common on modern vehicles as they have the benefit of reducing drag while not cooling, the only difference from the ancient ones is they are now automatically controlled. Here is the one for a BMW 5-series:

[7 wonders of the world]

Not sure if the drag reduction wll be quite as effective on a 7 

There are a few versions of the PRRT start istr I used the 82 degree soft spring which I think was light grey in colour

[ScottR400D]

Since when has a 7 been a ‘modern vehicle’? 😁😁

[Steve Sheldon]

Just use a standard thermostat as I found to my cost - too much cooling if you start drilling bleed holes - the engine will cope as designed.

[Miker7]

Now we're in warmer weather i'm watching my temperature with interest and wondering if i should go back to 88 degrees from my 82.

[ScottR400D]

6 hours ago, Miker7 said:

Now we're in warmer weather i'm watching my temperature with interest and wondering if i should go back to 88 degrees from my 82.

Why? 

[Miker7]

Cause the gauge doesn't get to 80 degrees unless I'm driving enthusiastically. It's often lower. Im a new owner and potter more than I drive enthusiastically. I'm aware the gauge under reads by 10 degrees but don't want the engine running out of the optimum range.

[ScottR400D]

9 hours ago, Miker7 said:

Cause the gauge doesn't get to 80 degrees unless I'm driving enthusiastically. It's often lower. Im a new owner and potter more than I drive enthusiastically. I'm aware the gauge under reads by 10 degrees but don't want the engine running out of the optimum range.

Ah, sorry missed that. 
 

But the 82 stat, as long as it’s working properly should be fine. Why run it hotter than that? 

Shouldn’t you be fixing the gauge first if you know that’s wrong? 

 

[SLR No.77]

17 hours ago, Steve Sheldon said:

Just use a standard thermostat as I found to my cost - too much cooling if you start drilling bleed holes - the engine will cope as designed.

In the standard K-Series Caterham install a small bleed hole is needed to prevent an air lock in the lower radiator hose. This has been tried and tested by hundreds of owners.

Stu.

[Colin_T]

I suspected mine had no thermostat in it, or had had its gubbins removed.

as it always seemed to run quite cold in winter - to the point where it still be getting slight warm up enrichment fuelling being added.

i was quite shocked to find a thermostat fitted when I removed the housing. 
I tested its operation and it was all working fine. 
 

maybe it’s a water pump speed thing, cruising along at 4000rpm rather than normal 2500-3000rpm ? 
 

At some point further down the line when I update the ecu and electronics to something considerably newer I was going to use an electric water pump and have that ecu controlled.