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MG MGB GT V8 Factory Originals Technical - EFI plumbing & heating question

I'm coming towards the end of my MGB 3.9 Hotwire build and have 'dry fitted' my machined EFI and all fits well. Now that I am looking closer at the installation can anybody tell me how they have incorporated a heater take off/control?

Is there an in line valve avaiable that I can plumb in to my existng heater and connect up to the original heater cable?

I will also need to look closer at the plumbing in general as the plenum heater is now redundant


R Weston

The earlier Golfs had an inline heater valve which seems to work well with one of the OE factory V8 heater hoses - beyond that its ingenuity.

I used a normally closed vacuum heater valve on my conversion engaged using a vacuum solenoid. The only problem is the heat is either on or off. It did work well in my case. I used an inline ball valve style unit on my four cyl. MGB that works great. It was originally used on a Chrysler. Here is a photo of the unit on my MGBV8
Evan Amaya

The intake manifolds on the 3.9's seem to vary alot but they will all have a heater take off point somewhere. I retained my 1800 MG heater valve and made up a fitting to adapt it to the range rover location. In my case on the front RHS of the engine manifold.
The very important thing not to forget is some sort of coolant recirculation facility while the engine is warming up.
This ensures that the coolant will circulate through the motor prior to the mechanical thermostat opening and allowing water into the radiator. therwise hot spots, over heating, all sorts of problems.
The 1980's RR's (and the RV8)had a short bit of hose from the manifold to the back of the water pump. The later ones (at least my 1994 did) rely on a double heater switching valve. When the heater is on the water circulates ( returns to the pump) through the heater. When the heater is off the water does a U-turn at the valve and returns to the bottom hose, then up into the pump.


EFI inlet manifolds generally seem to have a 5/8" outlet to plumb to the heater. I used this along with a 5/8" inline valve from europa spares and 5/8" to 1/2" reducer to connect to the radiator. I had to open up the valve and reverse the innards so that its open and and shut position matched hot and cold on the control knob. In addition I use a metal pipe to run from the outlet at the front of the manifold to the valve located near the heater. This is probably the most inelegant part of the conversion as you end up with a whole series of hose - pipe - hose - valve - hose - reducer - hose all jubilee clipped together but it can still be done neatly enough. There is some more detail of my plumbing solution on my web site.

Re plenum heater - you can block off the hose that ran from inlet manifold to plenum heater by jubilee clipping a bolt into the open end - this was the TVR standard factory solution. But as Peter says you must have a thermostat bypass plumbed somewhere into the system - it normally runs from the front of the inlet manifold to the back of the engine front cover behind the water pump.

Geoff Richmond

Thanks all for the advice. I'm going to see if I can track down a valve and have a play with it over the bank holiday weekend.
R Weston

"the bank holiday weekend"

What's a bank holiday weekend? Is that why I haven't been paid by my UK client this month?
Edd Weninger

" What's a bank holiday weekend? Is that why I haven't been paid by my UK client this month? "

Edd, More bad news - there is another Bank holiday coming up at the end of this month! A successful weekend though, I picked up a heater valve from a Porsche 944 (for 2.20)on E-Bay that looks like it will do the job.
R Weston

This thread was discussed between 26/04/2004 and 10/05/2004

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