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Heater plumbing - differences between 143 and 160? 
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Post Heater plumbing - differences between 143 and 160?
A call for advice as I'm baffled! I changed from 143 VVC to 160 VVC late September and since then the heater isn't working. There seem to be some differences in the way the coolant plumbing is arranged on the 160 MGTF from how it was on the previous version but I'm struggling to see why it isn't working. The TF had two hoses that connected to the pipes to the heater matrix and I've used these to connect to the Spyder's heater hoses. As far as I can tell the only thing I could have done wrong is reversed the flow and return so unless there is a one way valve somewhere in the Spyder's heater system surely it wouldn't matter which way the water flows through the circuit? As the coolant warms up I can feel heat in the bypass circuit in the engine bay but nothing seems to be going to the heater pipes as they stay cold. When the main thermostat opens I can feel the flow start to go towards the rad but still nothing flowing around the heater circuit.

I've checked for kinks in the hoses and nothing obvious. Could be an airlock I suppose but there does seem to be fluid in the heater pipes, just cold!

Any ideas?


Sun Dec 22, 2019 4:11 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Do you have OE stat near the pump or a PRT?

Pretty sure the Metro heater matrix is just a 'radiator' with two pipes off it and no flow control valve.

I'd guess its an airlock in the matrix, it's a bugger for that if you've drained the system.

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Mon Dec 23, 2019 5:13 pm
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Post Re: Heater plumbing - differences between 143 and 160?
It looks like it has the PRT installed but would have been a modification as it came from a 2002 TF and as far as I know the PRT was introduced in 2004. As such I'm assuming the original stat would have been removed from the housing but I didn't check. To be honest it was a bit of a rush to install it. I'd had the 160 engine etc sat on a dolly since I dismantled the TF about three years ago and had intended to give it a good going over before fitting it this winter but when my gearbox bearings went and at the same time the HG started to let go on the 143 after a track day in late August I brought forward the swap and to avoid missing the good weather I chucked it in as it was. The pipes that make up the bypass loop seem overly complicated and I'm scratching my head a bit trying to make sense of the flows. From a brief overview it looks like the bypass loop will be the path of least resistance until the stat opens and once open the radiator becomes the preferred route so I'm struggling to see why the water would ever bother to go through the heater matrix unless there is a flow restrictor in the bypass. Maybe there should be one but it wasn't installed when the PRT mod was done, in which case the heater in the TF wouldn't have worked either! I never drove it before I broke it for parts as I bought it as an MOT failure so that is possible.
Might just be an airlock I suppose - I can't find a bleed valve at the heater matrix (but haven't got down in the footwell to look), If it is an airlock, how would you clear it? On the old system I'd drained and refilled a few times and never had a problem with airlocks in the heater circuit. This time, following advice, I filled it with the rear of the car lifted as high as I could get it so the header tank was about 400mm higher than the the level of the heater matrix and filled very slowly.


Mon Dec 23, 2019 6:27 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Front bleed for heater should be under bonnet on one of the pipes going thru the bulkhead. At least it is on my Libra as that's how the manual said to do it.

I use a garden pump sprayer to force coolant into the system via the rad overflow to expansion bottle pipe. Clamp off the heater pipe with the bleed and use pressure to force fluid (and any air) thru the matrix and out the bleed rather than back down the pipes. (set heater control to 'hot' also)

A pic of my PRT based layout here: 1-8-vvc-timing-t4194-30.html dunno if that helps. When I went from Metro GTa 1.4 to 143 VVC all those years ago i just plumbed the engine to the pipes I had. When I went from OE stat to PRT I only altered the rad pipework to accommodate the PRT, the heater pipes were untouched. I believe the MGF pipework links rad and heater together though around the hot outlet.

I don't think the MGF has a rad to exp tank hose like the metro (and OE Libra) has but it comes from that area around the hot outlet from the block. Also does the 160 have an oil cooler as standard?

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Mon Dec 23, 2019 7:44 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Correction, no PRT. What I thought was the PRT is actually just a plastic Y connector with the heater flow coming off the smaller side of the Y. The hot water is flowing fine through the big pipe, even when the stat is closed which must be using the small return pipe from the rad to the header, but nothing is going down the heater pipe at all as it is cold straight after that Y. I'm starting to wonder if the small branch of the Y is blocked.


Tue Dec 24, 2019 4:23 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Sounds like you have a blockage somewhere or air lock in the matrix, i've had that and it can stop flow down the heater circuit pipes.

Try blocking off the rad to exp tank pipe so it no longer has that path, thereby forcing it to go round the heater circuit?

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Tue Dec 24, 2019 5:02 pm
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Post Re: Heater plumbing - differences between 143 and 160?
I've noticed that when the engine is running coolant is constantly squirting into the header tank from the pipe that comes from the jiggle valves. I thought these are only supposed to open when there is air present and seal by means of a floating ball or similar when full of coolant. This suggests the jiggle valve is not closing so maybe this is short circuiting the flow, especially as I also have another bypass route courtesy of the radiator top return pipe that also goes back to the header which it seems isn't present on the MGTF setup. The bypass itself is also always open and that includes the OEM water bath oil cooler. That means that when the stat is closed the heater is one of four options for the coolant to circulate via, with the stat open there are five options. My next trial now the family have all gone home is to block off the pipes from both the jiggle valve and the radiator header return and see if that encourages some flow to the heater.

Looking back at the plumbing from the previous set up with the 143, there was no separate bypass loop, the only options with the stat closed were the heater or the rad top return to header. Might be on to something!


Fri Dec 27, 2019 1:20 pm
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Post Re: Heater plumbing - differences between 143 and 160?
I thought Jiggle valves are supposed to allow fluid/trapped air up into the tank but not allow it to return back through them into the system. However i've just read that "The idea is that the valve will be open to the passage of air but that water will lift the (ball) valve and close it" which makes more sense.

Yes the MGF has no return path to the tank direct from the radiator (like the metro OE libra setup has). Instead there is a return from the pipes somewhere around the engine's hot outlet that goes back to the tank.

If your heater circuit is blocked by whatever (and the stat is shut) that pumped fluid's gotta go somewhere. Or maybe if there are easier paths the fluid will use that instead. Have you only tested at idle?

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Fri Dec 27, 2019 3:24 pm
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Post Re: Heater plumbing - differences between 143 and 160?
My non VVC K series pumps water out all the time back into the expansion tank, there are 4 pipes coming off the front of the engine, 2 larger ones (about 32mm) which go to each side of the radiator & 2 smaller ones (about 19mm) which go to either side of the heater matrix. There are 3 bleed places, one on the pipe at the back of the engine, one on the heater matrix & one on the radiator, as I didn't use a MGF radiator I sandwiched a schrader valve into the top hose to bleed from there.


Sun Dec 29, 2019 5:33 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Update on this thread as I've now got heat again. I took some time to trace all the pipes and work out all the flow routes and I've come to the conclusion that I can't understand how the heater would ever take flow on the TF system. The flow to the heater matrix comes off a Y connector from the main rad flow pipe not far after it exits the cylinder head near the bulkhead. The outlet boss from the head also has a side connection for the bypass loop and the return from the heater matrix tees into this bypass loop only about 150mm from the outlet from the head. As such both the flow and return to the heater matrix are both effectively connected to the same place so the pressure would be equal so I can't see any incentive for the water to go via the heater matrix when it has the much easier route of going via the bypass loop back to the water pump side of the stat.

The TF has a shut off valve in the heater loop so there has to be a bypass but on the Metro based system in the Spyder there is no valve so I figured there is no need for a separate bypass. I re-plumbed it to remove the separate bypass, took the heater flow directly from the side outlet from the head boss and the return direct to the metal return pipe. I blanked off the Y piece on the rad flow pipe. Whilst doing all this I also installed a laminova but that is a different story.

This saved about a couple of foot of 16mm bore pipe and similar length of 6mm bore so a decent weight saving too!

the coolant I'd drained out went back in again, all bar about 1/4 litre so consistent with the reduced pipe length. The heater now works perfectly again so suggest an air lock wasn't the problem.


Wed Mar 18, 2020 6:07 pm
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Post Re: Heater plumbing - differences between 143 and 160?
Good to hear you sorted it.


Wed Mar 18, 2020 6:17 pm
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Post Re: Heater plumbing - differences between 143 and 160?
The metro and MGF have slight but significant differences in the coolant plumbing as you've found and trying to 'combine' the two probably gave the problem you had.

Well done Sanz, you've fixed your heater just in time for warmer weather!

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Wed Mar 18, 2020 7:38 pm
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Post Re: Heater plumbing - differences between 143 and 160?
sidewinder wrote:
you've fixed your heater just in time for warmer weather!


Had a run out to Stourhead (National Trust) on Monday morning - only 5 degrees outside on the way but glorious sunshine so we were both very glad of the heater working!

National Trust have now shut most of their properties so glad we siezed the opportunity!


Thu Mar 19, 2020 10:47 am
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