Hey all,

Would anyone have the part number for the "Assembly hose-heater to water valve (return)" from drawing J.412.089 for a 99 XK8?

My hose has collapsed. When the engine is hot, the hose is cold. One can lock a small vice grip in place over the hose where it bends to meet up with the check valve and feel the flow as well as the heat build up.

At some point, my vice grip will tear through the hose and I will need a new one.

Please and thank you,

Sabrina

 

Note - pipes 4 & 6 are flattened by design anyway (although I don't know why).

Could you explain what you mean by ...'One can lock a small vice grip in place over the hose where it bends to meet up with the check valve and feel the flow as well as the heat build up."

 

The problem with a flattened hose design is that as it ages, it is more prone to collapse or kink. For six years (six I know of, sixteen most likely) the hose has had flow when the heater valve is open, all of a sudden there is no flow at all in this particular hose. To regain flow, a special small vice grip helps while I locate the hose to replace it.


I can't find a dealer willing to sell just the hose, they want to sell the hose to the check valve, the check valve, and the hose I want as a complete assembly. Jagbits has the assembly for $102.42, about half of what the dealer wants. The vice grip was $2.99 at Harbor Freight.

 

Hi Sabrina.

It looks like it is only sold with the attached one-way valve and the hose on the other side of the valve, part number mja6739ac.

My suspicion is that it may not be the hose, but rather reduced flow in the system caused by a bad heater pump, bad heater valve or clogged heater core.

 

As to flow, I would tend to agree, except that when you squeeze the sides of the hose where it is kinked, there is ample flow and immediate heat build up--from stone cold to hot in 20 seconds.

I wonder how many "NO HEAT" heater valve and pump replacement fixes were 'fixed' not by replacement of the pump/valve, but by the concurrent replacement or re-positioning of the #6 hose in the process of replacement or flushing?

Do you show the correct assembly as either MJA6739AC or MJA6739AB?

What is the ID of the hose?

 

The AC assembly part number superseded the AB assembly, so both are correct. I do not have any more information on the individual hose.

Interesting thought...maybe you are on to something here.

 

Thank you.

Speaking of a simple fix. When my battery got old it would not hold a charge well and my car would, at times, not start (turn the key and nothing). I purchased a new battery and the problem went away.

Then I thought, it would be interesting to compare the voltage required to engage my existing ignition relay (under my hood in the same box as the heater pump relay) to a new relay. The 16 year old relay required 12+ volts to engage. A new 'replacement' from Amazon only required 10 volts to engage. The issue would not arise with the other relays (heater pump, horn, lights, headlamp washer, etc.) since the alternator would bring the voltage up above 12V.

Before replacing a marginal 'nominal' battery in the future, I would consider pulling the old relay, jumpering it and then see if the car starts. If it does, one might consider buying a newer 10V-trip relay. At the very least, jumpering it might get one on their way back home.

 

I am very interested in this thread Sabrina because I too have been fighting a no heat problem in my XK all over the winter. I replaced the pump. Then I direct wired the pump to cut out all the control stuff. Then I stripped/checked the water valve. Then I disconnected the heater matrix and flushed it though (it was clear). Nothing got it working!

In the end I decided it has to be the hoses or NRV's. With no skin left on my knuckles and my fuse burnt out, I stuck it in my Indie's workshop and asked him to fix it! Sound familiar?

 

The heater return hose is just old (and a bad design) and when the throttle was adjusted, leaning on it caused it to kink/collapse semi-permanently.

Initially, it appeared electrical since the center instrument bulbs both went out at the same time. Thinking back, it was just a coincidence. However, checking the electrics did lead to the replacement of the ignition relay with a new one.

A return hose from the supercharged version (that has a 180 degree bend that is molded round rather than flat) is on order. It was $11 compared to $93 for the XK8 hose.

It will need to be cut in half (the 90 degree bend removed, and possibly used on the other end of the check valve, routing it to the outside of hose 5 rather than inside of it, so the top hose can approach the heater core at a better angle) and the hose that connects the shut off valve to the check valve will have to be rotated/shifted slightly. It should work better than the original. If not, then the $93 hose will go in.