91 5.3L XJS coupe, heater core leaking, misting up the windshield. Wanted to know if there is any danger to temporarily bypassing the heater core until the part comes in, I'd like to drive it in the meantime. Wanted to hook up a 4' long 5/8" hose from the passenger side all the way over to the driver's side, under the air inlet drain tube. Any reason not to do this?

 

I don't see any harm in it.

Others will chime in.

Don't forget to bleed the system

Cheers
DD

 

I was going to take hose #22 and #25 loose, and attach a 4' hose from the engine where I took #22 loose, and the other end to the end of the pipe # 27 going back towards the front in the attached diagram:

 

When you do replace the heater core make sure to replace the O rings on the feed and return pipes, these leak. I used XJ40 O rings on mine they are an upgraded part and fit my 89 perfectly.

 

I would NOT do that.

Reasons:

HOT HOT coolant is now travelling DIRECT to the COOLED side of the radiator, via that pipe, thus preheating the return coolant TO the engine.

Factory design closes the tap, STOPS the flow. When the tap is open, the heater core dissipates a lot of that heat, and the systems does what it does.

Gareth in Manila did that with his 1990, loooooong time ago (who needs a heater in Manila), and had serious temp issues. I suggested "capping" the engine outlet, AND the return pipe. Once this was done the temp issues were sorted.

I know that Manila is way different temps to where you are, but I still dont suggest the hose by-pass.

Just my experience.

 

You could buy a used temperature switch and fit that to the engine Hot water exit rail connector on the rear of babk A. It is only screwed in... The other side then should just need some Kind of plug to stop sucking. So a larger screw with a clamp on the hose should be sufficient.

 

Grant's point has got to be right.
If Jaguar are happy to block the coolant passage under hot conditions (ie heater valve closes automatically at coldest aircon settings) then this is the thing to do. Just block the input hose (22) with a suitably sized bolt and Jubilee (worm drive) clip. Then undo the return hose from the firewall exit pipe (25) and do the same. Then blow out the coolant from the heater and job done.
Greg

 

Done a lot of ways in various critters. I've not had the "pleasure"
of a V12. Well, way back, for a short time, a Packard V12, 34 vintage as I recall. Fuel way more than a poor college kid could handle, even discounted by my employer from 22 cents a gallon to a mere 20!!!


My daughter's VW Passat suffered terminal plastic heater disintegration. Her gal pal's mechanic, looped the hoses. I looked at the car.I saw why he didn't just plug at the sources. Avery complex hose system??? but, why not just plug each end? don't knw, but so far, no ill effects, Well complaints of cold. Why, in CA???


Way back when, USA critters had summer winter valves at the source. Close in summer, open in winter. Manual, done under the hood/bonnet.


My Jaguar mas two heater valves. One the plastic vacuum operated one. and, the one, I added on the other hose. Ordinary manual off/on lever operated, standard plumbing gear. so, in summer, no hot water at all in the cabin. I can run the fan as a power vent.


Carl