Dribbling Hose

[mudguard]

Yes JK - particularly as I had the sump off not much more than a year ago and there was no evidence of break-up. 

In retrospect there were a few distinctive symptoms of the obstructed exhaust caused by the failed Cat which I dismissed at the time but which I would now take much more seriously.

On cold starting, the button press would rotate the engine about half a revolution before stopping. The second press would spin it strongly and it would then start. I know what you're thinking. The battery was new, fully charged, and the voltage was high.

On switching off the ignition, without the rad fan running, the engine would stop immediately. Not slowing down rapidly as you would expect, just an immediate stop.

Finally, one of the emissions measurements on the MOT was only just inside the boundary.

[revilla]

The "missing bleed ball valve" is a pain. There's some rumour been going around the Rover world on the internet for many years that there's a benefit to knocking it out, so people poke a big screwdriver into the bleed from the outside and punch it inwards with a hammer! I've been involved with quite a few VVC engine builds lately which has meant buying a few used manifolds off the internet and I've now reached the point where I insist on the seller sending me a photograph of the ball valve before I'll buy as so many of them are knocked out. All it achieves is opening up a bypass circuit for coolant through the expansion bottle which robs the main circuit of flow - including significantly reducing flow through the head itself and through the proper bypass circuit, which as you note prevents the thermostat from opening properly. Unnecessary coolant circuit mods are one of my pet hates - and in my opinion if everything is healthy and the engine is anywhere near stock configuration there really shouldn't be much need to modify it at all. Did you replace the lower manifold to fix it? Or did you find a way to replace or substitute for the missing ball valve? If so, please do share.

[mudguard]

Nail on head Andrew - the "unwanted bypass" is exactly what's happening in my engine. 

For some unknown reason, there is considerably more flow through this bypass route now after all the work, but there was always some. That, by the way, explains why things got considerably better for a while with a hole in the stat I drilled - the hole allows some high-temperature flow through to counteract the effect of the bypass.

The chaps who did the recent work aren't in favour of holes in thermostats, so as a workaround they've used an 82 deg stat, which as it's always open to some extent, consistently beats the effect of the bypass. In terms of opening when it should, it seems a perfect workaround. The downside is of course the engine runs a bit cooler than is ideal, but not overly so, and there's less heat in the interior. At some point we might revisit this - they suggested constricting the flow in the bleed hose or finding a replacement manifold - but for the moment I intend to enjoy an overheating-free car, and slightly too cool is a huge improvement over always too hot.

BTW, I can't take personal credit for any of these findings or any of the work. I'm just reporting the findings of the chaps I paid to sort it, who clearly deserve their rep as K-series engine builders.

[revilla]

I think you'll find that most people with K Series Caterhams run 82 degree thermostats as the default anyway. Mine has an 82 thermostat and the small additional drilled hole.

With an 82 degree thermostats and no hole I found that the temperature used to cycle up and down a bit (the water in the radiator chills, when the thermostat opens you get an inrush of cold water which causes the thermostat to close again in a continuous cycle) and it was a pain to refill (it always ended up with air trapped in the thermostat housing which insulated the thermostat and stopped it from opening).

After drilling the hole the temperature cycling was eliminated (by allowing some residual flow with the thermostat closes it stops the water in the radiator stagnating and becoming over-cooled) and it fills easily without any of the "jack it up, massage hoses" nonsense.

Running a K Series too cool isn't best for the head gasket as it reduces the clamping force from the head bolts (aluminium expands more than the steel of the bolts so the whole sandwich gets tighter as it gets hotter) but thermal shock and constant temperature cycling aren't good for it either. 82 seems to be a reasonable compromise in a Caterham. Personally I would still drill it but if it's working fine for you then go with your engine builder's advice, they clearly know K Series properly.

I reckon that as a solution to repairing a manifold that has been "modified" a simple restrictor could well be the best solution, allowing air bubbles to bleed off relatively easily without permitting excessive coolant flow. I've never found any kind of ball valve insert that you could sensibly fit into the outlet.

[Tony Whitley]

Tazio, isn't Dribbling Hose the name of a village in the Cotswolds?

[StevehS3]

This is an interesting read from 2012.

edited to say it's now not at all readable :(

[SM25T]

I have that as an emailable pdf if required. You can probably also find it in the LF archives via this site. September 2012.

[StevehS3]

http://lowflying.lotus7.club/2012/2012_09_02_Coolant.pdf

[revilla]

I have to say at this point that I've always had a problem with that cooling system modification. Before deciding to say anything this morning I re-read it again, just to make sure I was understanding it correctly.

So this modification is in fact simply redirecting the the coolant flowing out of the head through the bleed port and the expansion bottle from the radiator return circuit to the bypass circuit. But the thing is, in normal operation there shouldn't be any coolant flowing out of the head through the bleed port; it's an air bleed only and a ball valve should restrict any flow of coolant to a trickle. If there is no flow, it doesn't matter where you route it. So as far as I can see, when everything is functioning correctly, it should make no difference whatsoever.

OK, it may make the system a little easier to fill initially, but in my experience a tiny bleed hole in the top of the thermostat flange to allow airlocks to escape and filling it slowly from the highest point eliminates the issues here anyway; I never have to jack mine up, massage hoses aggressively or anything like that.

After the discussions we've already had on this thread, I can see how it might help on a car which has a malfunctioning or missing ball valve in the bleed port. If there is significant flow out of the bleed port this will compromise the proper bypass circuit which is responsible for opening the thermostat (only the bleed flow hits the wax capsule of the thermostat when the thermostat is closed as the flow from the radiator is blocked off be the thermostat itself). This modification will at least route the robbed flow back into the normal bypass circuit which should help ensure that thermostat opens when appropriate, however the coolant flow through the head will still be compromised on a K Series that's really not a good situation.

The modification does also have a downside. Especially in a Caterham when being driven enthusiastically, any flow which does occur through the bleed / expansion bottle route is likely to carry some air bubbles. If this occurs when the thermostat is open the bubble will be carried away through the system harmlessly and will eventually end up in the head where they will be cleared by the bleed (that's what it's for). If it happens with the thermostat closed however, the modified configuration will route these air bubbles straight round the bypass side of the the thermostat which is a known problem area for airlocks. In this case the air bubbles act as an insulator around the wax capsule and prevent the thermostat form opening, which also means that it then struggles to clear the airlock.

There have been several cases where people have done this modification and found a tendency to discover the expansion bottle full to the top and air stuck around the system after a blat, with cooling significantly compromised.

So my personal opinion (for what it's worth) is still as I stated earlier; in a reasonably stock cooling setup where everything is functioning correctly, there is no modification necessary. The design is actually sound provided that all of the components are functioning as designed. The only exception being that I and many others have found the drilling of a very small bleed hole in the top of the thermostat flange to be significantly beneficial. This allows air bubbles to escape while filling and also allows the water in the radiator to continue to move slowly when the thermostat is closed, reducing the tendency for it to be become chilled and cause temperature cycling and thermal shock with the thermostat cycling between wide open and fully closed.

If the cooling system isn't working properly, something somewhere isn't functioning as it should, and the correct thing to do is to identify the faulty component and fix or replace it not, not fudge the system to work around it.

Component failures worth investigating include:

• Blocked / Missing bleed valve.
• Faulty thermostat / airlock from filling (or even the wrong thermostat fitted).
• Clogged up cooling system (I've stripped engines that have been treated with K-Seal and similar for leaks - please, please never put that stuff in your engine! Over time it results in thick deposits all over inside, around and in between the cylinder liners, and does clog the radiator).

I qualify all of this when I talk about about a reasonably stock cooling system as I have seen issues with things like triple-pass radiators. These may well work for cooling on track at high RPM but at low RPM / idle the water pump struggles to provide enough flow due to the increased resistance of the radiator. I've seen a couple of cars now where triple-pass radiators have led to overheating issues at idle. Unfortunately being installed on track cars that generally get a good thrashing and become very hot, compromised cooling at idle and low RPM tends to mean heat soak into the head from exhaust primaries while on a cool down lap or idling in the paddock and that's a recipe for head annealing as the areas around the exhaust valves are already the most vulnerable.

[CageyH]

No "traditional" thermostat and a PRRT avoids this issue completely. I lost my ball valve when I went throttle bodies and have run my car at -15 degrees up to 42 degrees C and have never had an issue with it, nor have I had to blank off the radiator as the PRRT effectively does this for me.

[revilla]

Yeah I guess once you're on TBs with no bleed ball valve you're well away from a "resonably stock cooling system" in the sense I meant it. I which case a PRRT solution is probably the best as you say, and maybe the "Low Flying Coolant Mod" is not a bad haflway house in this case.

[7 wonders of the world]

The light spring 82 degree PRT works perfectly, and holds a constant temp, my K was stop on with this - assuming its installed correctly.

Cant remember what colour PRT the light spring 82 degree is now though sorry.

Found it -  

PRRT Colours

Cream is 87°C With Medium Spring: first being used on FreeLander & MGF/TF.
Black is 82°C With Hard Spring: Not suitable for Rover K engines.
Grey is 82°C With Light Spring: Latest being used on Freelander (MGF/TF ?). Land Rover replace the old stat (87°C) with this one if they have to open the coolant circuit. THIS IS THE ONE YOU WANT !!!

[CageyH]

That is the one I have.