Top hose thermostat

[paul richards]

I fitted a QED top hose thermostat housing to my K series engine a little while ago and reused the the 82 degree thermostat that was fitted in the normal thermostat housing. This thermostat had a 3mm hole drilled to aid bleeding. The car runs fine but runs a little too cool for my liking in normal ambient temperatures. I therefore changed to a new 82 degree thermostat with no hole. Temperature now comes up quicker but will rise to around 100degrees or even a little higher and will then drop very quickly to 80 degrees. I assume this is when the thermostat opens.  It then stays at 80 but gradually climbs again to 100 and then very quickly drops again. Picture attached to show how it is plumbed. Yes I have replaced the original thermostat with the recommended spacer ring. I have also tried 2 new thermostats with the same result. 
Any ideas why it is doing this?

Edited February 23 by paul richards
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[7 wonders of the world]

The 'bypass' arrangement on the qed start is a small bore which will affect the ability. Of the start to react quickly. 

Have you checked if this line is clear.. Especially the entry into the expansion bottle.. This is usually a very small. Bore that can often become restricted meaning the stat has to rely on conduction and convection to receive a heat source due to. It's location.. Much slower than a direct source of hot water. 

Also the tee piece with the kit what are the leg sizes on it....? 

Yours appears to be an aftermarket brass one teed into the bleed from the head by no 1 into the expansion bottle.. Hence both these sources are venting via the same small bore outlet. 

I haven't seen inside the qed casing so I can't say if the stat operation affects this bleed as it opens as it ideally should. 

A bypass system. Would normally. Engage the stat to control the flow of both hot and cold sources however due to the qed location I suspect their bypass is indeed more likely a renamed bleed. 

The land rover prtversion is a full. Flow bypass set up which works very well and locates in the bottom hose maybe consider this as an alternative istr it's the light grey 82degree soft spring version I used with a 32mm tee. 

[SLR No.77]

As a test I’d be tempted to remove the thermostat bypass pipe and use the thermostat you have with a hole to check whether this makes it behave any differently, if there’s no change this will concur with Neil that there’s not much coolant being fed by the bypass pipe. In the o/e Rover install there would have been a small ball valve in the inlet manifold, IIRC a one-way valve, do you still have this or is it an open line with the Jenveys fitted?

Stu.

[Englishmaninwales]

Paul,

I run the QED with the bypass outlet plumbed via a T piece into the lower header tank outlet to submarine pipe so bypassing the header tank. I fitted the CH to header tank hose with a 2mm restrictor fitted to replace the jiggle valve (on the standard manifold) when I fitted TBs.

Malcolm

Edited February 24 by Englishmaninwales

[paul richards]

Gents. Thanks for your suggestions.
Neil. I was coming to the conclusion that something was wrong with the bleed/bypass as it is not allowing hot water to reach the thermostat. As you suggest it appears the thermostat is only being operated by convection/conduction. 
Stu. I can’t recall whether there is a small ball valve in the cylinder head outlet but I did wonder if this could be the problem as I understand they are prone to sticking. In any event this is a very small orifice which could be easily blocked. I’ll take the hose off and give it a poke. Don’t really need some form of valve? I seem to recall someone advising to remove it.
Malcolm. Your idea of tapping into the hose between the header tank and the submarine pipe seems like a good idea. I’ll investigate and report back in due course.

[Englishmaninwales]

Paul - Just a further thought - If you are running without a giggle valve or restrictor in the CH to header there maybe reverse flow     back into the CH prior to stat opening. This may explain the rapid rise to100 and fall when stat opens?

[Graham King]

The QED remote stat is supplied with an 8-16-16 tee piece as it’s meant to splice into the 16mm hose out of the header tank, not into the 8mm hose from the CH to the header tank. I had one installed in my old k-series for a good number of years and never experienced the issues you are referring to Paul. 

That said I was never convinced the QED solution was a perfect solution as it did seem to result in the engine cycling between normal to low temps until it eventually evened out. 

Graham

[paul richards]

I’ve done further investigation and no problems with blockages in pipes or waterways although the orifice in the top of the standard header tank is very small as standard with a narrow metal insert to stop the plastic crushing. 
Graham - Thanks for your response. I was intending to follow Malcolm’s advice and put a T in the 16mm hose from the header tank rather than the 8mm outlet and you have confirmed it. I note on QED website the kit does in fact show a 16/8/16 T piece.

I’ll order the T piece and report back in due course. 

[Simon.Rogers]

As per the Doctor above.

Your bypass from the QED runs largely back into the head.  It needs to T in to the small outlet at the bottom so it goes back into the main flow of the system.

This will warm up the system a little faster and then also not keep making these big changes in temps.   I have run one of these on my SLR since day 1 and you will get that initial swing on first opening of the stat but it should be fine ofter that.

[paul richards]

Update. 
The lead time to get a suitable brass T piece is around 6 weeks (from China) so I opted for a plastic T from Car Builder Solutions and fitted it earlier today in the 16mm bottom outlet of the expansion tank. Took it out for a run and it quickly warmed up and never went above 80 degrees. Result. Returned home and left the car ticking over. Fan kicked in at a suitable point and switched off after it had cooled. 
I’ll order a brass T from China and replace the plastic one in due course. Many thanks for your assistance. 

[paul richards]

Brass T piece finally arrived from China so I have now fitted and shortened/tidied the hoses. Took the car for a quick test drive and it performs exactly how I hoped. Picture below as it might help others. Many thanks again to those who helped with their advice.