I’m getting ready to start my conversion to triple SU’s and as part of that of course replacing the intake manifold. I’m fitting a 4.2 style, and have a question about the thermostat housing. What’s on there now is a fairly long unit, which includes a small rubber hose fitting that attaches to the radiator. See pic 1.
I’d prefer to eliminate this, and go with the more common housing as shown in pic 2.
For the life of me I can’t figure what the small hose is supposed to be accomplishing… I’ve looked in the parts books and online and can’t find anything.
Can I use the adapter in pic 2 and just block off the small hose attachment at the radiator?
Not sure I follow your question. The thermostat fits inside the new housing, and the new housing has the connection to the radiator and the bypass hose to the pump…
In pic1 you don’t see the bypass hose, as it’s under the radiator hose. It’s the small hose, wire tied to the large radiator hose, that I don’t understand
Sorry. I think I misunderstood your question. There are several members of the forum who’ve put triple SUs using the Series 1 4.2 manifold into S1.5s, so hopefully one of them will be able to verify your proposal. The thin pipe between the manifold and radiator on the S1.5s and S2s has been discussed on the forum several times. As I recall, it has been speculated that it was added to ease bleeding air out of the cooling system.
It bleeds air automatically and is a common Jag feature after the late 1960s when engines began to run hotter. Yesterday I was fitting a new rad to the XJ 12 that uses an air bleed about three feet long from low on the left inner fender, up over the radiator and all the way across to a banjo fitting at the top right corner. I’ve always put it down to a combination of Jags having issues with correct coolant filling, and alloy heads that don’t like air pockets, plus low bonnet lines and frequent use of crossflow radiators meaning the typical high spot of the cooling system is not always obvious.
On the S1.5/S2 pic the spigot is often blocked with crud but in theory I think any air or steam pockets from around the combustion chambers broken up by turbulent flow and bleed high into the top of the bulbous thermostat housing and assuming the jiggle pin or plain hole are uppermost the air bubble is bled into the top tank and from there to atmosphere via the normal coolant expansion vessel headspace. I always try to jack Jaguars nose-high when filling, to minimise any entrapment in the first place, plus of course putting the heater on hot and checking/topping up after running the engine to circulate the fresh coolant. I’ll be finishing off the XJ12 filling today.
Morning Robert,
On my '68 I used a 3.8 manifold and blocked ‘it’ off. Has worked fine but like Peter suggested I’m very careful to bleed the system by having the front of the car up in the air.
Cheers,
LLynn
I cleaned my jiggle valve but still didn’t trust it (didn’t think about raising the front of the car) so I drilled a hole in the thermostat to assure an easy bleed.
My SU set came with the housing in your picture 2, and my S2 came with the picture 1 housing. If memory serves the bypass design is considerably different; 2 uses the slot in the side with the big sliding cap, 1 has the pipe with a plate bypass thermostat (not sure of the names of the two types, never paid attention, however both sets had a standard non bypass thermostat in them when I got them). I liked the design of picture 1 better, the bypass flow seemed more efficient, so I went with keeping the S2 parts on the triples. By the way the S2 parts have a tab cast on them that blocks the side slot on the older manifold, so it seems as if Jaguar intended them to be fully interchangable, and for the record the S2 parts work great on the older manifold.
Hi Robert I’ve played around with these fittings over the years, what with racing, Weber carbs etc etc. I would urge you to install the manifold extension off the Ser II onto the Ser 1 manifold, and keep the area Ser II stock. As you may be aware the water pump is different between the two series, because the bypass arrangement is different, which means that you will have to change it as well, or do some kind of jury rigging of hoses (nasty job). Secondly you will have to install an extension into the top big hose to the rad as that hose in stock form is too short, once the extension is out of the system. There are other problems - I’m away from home so I can’t go and have a look, and can’t recall everything, but trust me - using the extension and it’s plumbing is a whole lot simpler.
P.S. As I think about this I’m not sure the Ser I water pump is compatable with the Ser II bypass system. The Ser I puts the bypass water through the rad - the Ser II puts it back into the pump.
ROW S1.5s (fitted with SUs) feature the same longer thermostat housing as the US Federalized cars with Stroms so your conversion would be more period correct, albeit to the ROW spec, if you reused it rather than the new housing. As David says above the housing will bolt right up to the SU manifold and will require no plumbing changes.
Thanks to all who responded. After thinking about it I’ve decided to keep the S2 extension in place. Looking at it it seems to be a better bypass system. AND my car temp was running fine with this system in place, so why fix something that’s working.
“Will require no plumbing changes.” Incorrect. As Terry Sturgeon points, out, there are major plumbing changes required to make this switch. The complication arises from the difference in bypass designs: the water pump and radiator need to be changed to accommodate the S1 bypass system. Changing the radiator is a major deal, because the S2 downflow radiator mounts from the sides, in order to allow room for the A/C mount and reversed alternator. The side mounts also carry the fan shroud and A/C condenser. So now you need a water pump, radiator, radiator brackets, cooling fan, shroud and alternator mount, plus there would be no way to mount the compressor or condenser if you have A/C. You would also need an S1 picture frame with the fan mount welded to the top rail. When you are done, you would have taken a major step backwards: a less effective bypass system, no A/C, and less than half the airflow. Don’t be too quick to pull on this string.
The little hose on the S2 system is a bit of silliness that is there to bleed air on the initial fill. Most thermostats will have a small hole or bobble valve which would accomplish the same thing. Once the air is bled, it serves no other purpose.
I don’t think so. This is a pic of a 1968 home delivery Canadian S1.5. It is an almost completely original, low mileage car that used to be in the neighbourhood.
Quite. There is one difference, though, and that is the breather pipe that goes to the trumpet plate. It’s different inasmuch as it’s just a little shorter in the ROW cars. Probably just a matter of lopping off an inch or so at the trumped plate end.
Thanks Nick. That looks like what I’m trying to do, and if I use the extension on the front of the manifold I’m not changing any plumbing, front or rear. ( ok minor changes on the rear. Two adapters are horizontal rather than vertical. I can manage that one)
I see the problem. The original question was whether the S1 “short” thermostat plate could be used instead of the S2 “long” adapter and thermostat plate. And I think we agree that the answer to that is no.
