I am experiencing a problem with my 99 XJ8 where I am getting no heat at all.

I have removed the electric coolant "aux" pump and it is working fine but the "heater valve" doesn't seem to be working.

When I look thru the valve the top ports that align with each other are wide open. The bottom "offset" ports that appear to control flow to the electric pump do not allow water to pass thru. I have taken the solnoid off and tried pushing on the valve pin and it will only barely move.

Basically if I push or turn the valve "pin" no water will flow thru the bottom 2 "offset" ports.

When I apply 12v power to the solnoid, it clicks like it is trying to do something but I don't see the pin moving much (if any) thru the top 2 ports.


Basically I guess I don't know how the valve is supposed to work to know if it is working correctly. Any insight would be greatly appreicated. I would like to try to repair the valve if I can as a new one costs $350...

Also, I am considering just by passing the valve by connecting the hoses together with couplers, any issues with that approach?

Thanks....

 

Its a normally open valve, but they can stick cl0sed. You can bypass it in the winter and block off again in he summer cause the ac will not overcome the heater core temp without shutting off the coolant flow. Ie..heat all the time. Or you can buy 1 used. Im sure ken at motorcars on here has one or andrew. Jagtechohio

 

The CHEAP answer is to bypass it with two hose connectors. Connect the two TOP hoses together. Connect the two BOTTOM hoses together. It will always flow for winter heat. Summer time you will have to cap the system, or return it to the water valve for control.
Mine did the same. As I investigated, I found out that the rubber stoppers in the valve had swollen up. Two people form two different shops informed me that I had used a chemical in there to "restore" or "clean" the radiator OR that I had a petroleum product in there like OIL. Either of those would make the rubber swell.
If you replace the valve, you will need to flush your system. Then flush it again. Then flush it AGAIN. The valves are not cheap and they take a bit of time to get in/out.
Write me if you have any more questions about this. I am vague sometimes. davidlthies@hotmail.com

 

unfortuantely, last month i had the same problem with my 98 VDP. in, what seems like, my never ending repair/upgrade of my car i checked the aux pump, which was working fine so i replaced the heater control valve. heater is working like a charm now.

i bought the heater control valve from ebay for $50. i got a good deal since the person i bought the unit from included the whole "spider web" connections (all the hoses from the expansion tank, etc) along with the aux pump. i lucked out since i need to change the heater hoses under the intake manifold next week and will use the "new" hoses since they are in better shape than mine.

 

I have the same problem with my '98 XJ8. I have run through all possible avenues thus far, short of removing the heater core. My thought is that the heater core is plugged. I got a wild hair today to check the voltage coming to the valve. There is a steady stream of 6.5 volts to the valve. Is that correct, or should it be 12 volts? Further, I am getting 6.5 volts whether the car is on or off as well as if the heater is on or off.

My understanding is that it is "energised" for closed" and "not energised" for open. My dilema is why I have power at all times??? Is this a relay issue? If so, which relay is it. I referred to my JTIS for about 2 hours trying to locate a solution but I didn't find anything.

Any takers for this one?

 

^^^ if memory serves me I believe you should see batt+ when energized at the valve. You may have an AC ecu failure. A cheap check and fix as fell is to run a jumper wire from the Aux pump + to the + on the valve. Also would recommend disconnecting both heater core hoses and useing a rubber tipped air blower. blow out the core, there is nothing better to blow out crud

 

Thanks for the reply Brutal, I used a standard Voltmeter for the voltage reading...where would I see Batt++? I am going to bypass the the valve today to see if that soves the problem and then I will address the vavle further. I really don't have a way to keep coolant from getting all over the place at the moment, so I don't want to break into the heater core hoses until later (it is raining here for the weekend).

What is the purpose of running the jumper wire from pump to valve? Is this to let the pump's power energise the valve in case there is a short somewhere?

Thanks again.

 

I know this is an old thread, but I have experienced a problem with my 98 xj-8 heater so I am passsing this info on. The voltage feeding the heater valve cannot be thought of as on-off. The valve is normally open in the heat full-on position. If you set your temp control to HI inside the car, you will see 6.75 volts going to the valve...this leaves the valve wide open for full coolant flow. If you lower the temp control to 75 degrees, you will see the voltage change to 13.75 for a couple seconds, them 6.75, then back to 13.75....This valve is modulated.... in other words, it is being fed 13.75 for short periods of time to close the coolant valve when you require cooler temperatures. The cooler temp you set inside the car, the longer the 13.75 duration. If you are having problems with intermittant heat , you can disconnect the heater valve at the connector when the heater is working on HI. This will leave the valve in the open, or full-on position. Run your car for a few days and see if this fixes your problem of having poor heat. If it still is intermittant, it is probably the aux water pump, not the heat valve.

 

I want to bypass the heater valve to cap off the flow to the core so my ac works. Which hoses do I dissconnect?

 

So the problem I had with low heat was that the heater valve was bypassing from top ports to bottom internally in the valve.
I went the route of the blend flap because I was getting a little heat, but the blend flap was working fine.
After some checking to verify the pump was pumping and the valve was stroking, I removed the valve.
The top ports in the valve are a straight through ports always open to return pressurized water from the heater matrix back to the engine and expansion tank at the "T" connection.
The bottom port is actually the on/off valve for the suction side of the pump, draws hot water from the engine Cylinder heads, through the valve to the suction side of the pump, then through the pump for flow and pressure to the heater matrix.
If the valve shunts between the top ports (return to engine / cold return from heater) to the bottom port (pump suction / hot water from engine) , then the pump will short circuit - water flow wise not electrically, from the discharge back to the suction (high pressure to low pressure), and you will only get a very low amount of heat in cold weather.

I am looking at disassembling the valve which is proving to be a bit difficult - these do not look to be assembled so they can be repaired.
So for now, it is the cheap fix with a few hose barbs and clamps.
I don't think I would trust a used valve considering what i am discovering in mine until I fully understand the valve, but I am not sure I buy the explanation about chemicals swelling the seals - those seals are synthetic rubber pretty immune to a lot of stuff in the OAT, plus heat/cold cycles. I would believe crud in the system making the valve stick open or closed, and the shunting around the pump.

 

That sounds like the DCCV as used in S-Types - pics etc are in that forum if so.

 

Fortunately I have two similar XJ8's, a 2000 and a 2001 (glutton for punishment). One heater works, the other does not and they both have the exact same valve and hose setup. It is nice to be able to compare working / non-working side-by-side. The 2001 will bake you right out of the car and controls temps perfectly.
The valve is a Denso MNA6711AC like the one below which is what I believe to be the correct valve. I am thinking there should be a seal between the top ports and the bottom valve that the actuator stem passes through, it must have failed somehow.

I'll know more if I can get the valve apart without destroying it. The Yellow spot is where I think there should be a seal - or that path between the top and bottom pump side is open only when no heat is needed and the bottom ports are closed - that might make sense. that way the heater core only gets a little heat to stop condensation freezeup in AC mode.





Denso MNA6711AC Top ports are straight through, bottom offset ports are open/Close

For more followup, my heater core was not plugged - if flows clear water in both directions and no crud came out of it - captured in a bucket. Also with the valve bypassed, I get tons of heat all the time, so I will either have to pinch the supply hose to the pump, disconnect the pump, or sort out how to control temperature On/Off until I get a replacement Valve. I think a permanent bypass is not the best way to go.

Best new in the box price for this I have found so far is about $350

 

Just to pipe in, I did find a used valve on e-bay when my heat went out last fall, and so far it's been fine for me (it did come off a relatively low-milage car though). Exact same symptoms though, and even testing it, it did flow SOME even with the pump not working, which I assumed was just to keep flow through everything, but when it was called upon, nothing. Took about 10-15 minutes to replace, which was far easier than trying to repair prior to sourcing more parts. I kept the spare pump with the intent to fix the brushes and clean it. Guess what never happened yet lol

 

After tearing down the valve, I discovered it is actually a 3-Way valve. What I was expecting to find as a seal between the upper and lower ports is actually a functioning valve seat.
I also noted the materials in the valve seat are very durable and seem to be the type of seals that resist different cleaning solvents.

So valve operation is
Un-powered: [LIST]
- Top ports (return from Heater Matrix) straight through (always open);
- Bottom Ports (feed from Engine to Pump Suction) - OPEN
- Between Top Ports and Pump Suction lower port (Pump Discharge to Pump Suction) - CLOSED
Power Applied - variable Voltage
- Top ports (return from Heater Matrix) straight through (always open);
- Bottom Ports (feed from Engine to Pump Suction) - CLOSING as voltage increases to 12VDC
- Between Top ports and Pump Suction lower port (Pump Discharge to Pump Suction) - OPENING as voltage increases to 12VDC to reduce hot water from engine flowing to the heater matrix

It looks like my valve is functioning as designed, so why low / no heat when?
- the pump in pumping well - no blown fuse, good relay;
- the Valve is operating - not stuck - no blown fuse, good relay;
- the heater matrix is not plugged;
- no blockages in the feed or discharge hoses;
- hot water is available at the valve lowest intake port.

One of our other forum contributors lends helpful advice:

The varying voltage to the valve comes from the Climate Control Module based upon thermal sensors in the heater discharge and return airducts. \
If Jaguar applied standard Climate Controls, then this is a sensor based computer that senses temperature with thermisters or RTD's, feeds back the signal the the climate computer to vary the control valve in heat mode. (Some people may call this valve a blend valve, but I think the XJ8 also has an air blend flapper valve not to confuse the two).

If one or more of the thermal sensors used for heating mode has failed, then the climate control module will not allow the heat valve to be open enough (lower voltage to valve) for heated water to be drawn from the engine through lower valve port to the pump to the heater matrix, and will recirculate through the valve. that will be the next part of the tests.

A quick test that the valve is not stuck closed - provided your pump is functioning - is to simply unplug the valve at the connector and go for a drive. If you get cooked out when the car is up to temp with the heater on, the valve is not stuck closed. plug the valve back in and your heat goes away, then the fault is in the Climate Control circuit, either sensing in heat mode or the voltage control to the valve.

 

All,
I removed my heat valve bypass hose barbs as Spring has Sprung here in Colorado, reconnected my cleaned and rebuilt valve. Just for satisfaction I put 12VDC on it and it CLOSED fully.

FULL Closed of course means you will get NO hot water from the engine circuit as shown below.





Between my two XJ8's, I discovered another quick test - assuming your heater core and water circuits are clean:

Remember that 12vdc or so at the valve connector = Valve CLOSED, not OPEN. The valve is OPEN with no voltage meaning you should get heat if the valve electrical connector is disconnected.

If you have no heat, set the heat to the max which should show "HIGH" setting after 90 Degrees F. Heat? possible Controller /circuit problem

If you still get no heat after a few minutes with the engine warmed, the pump might be at fault.

You can easily and carefully put your hand on the pump and you will feel if it is running.

Pump Running on HIGH heat setting and HEAT = bad controller / thermostat / thermostat connection to controller / open circuit voltage to valve.

If you change the heat setting to normal temp, pull the valve connector and measure the voltage from the controller with a volt meter. IF you get 3VDC to 12 VDC, it is a stronger possibility the valve is indeed bad, or you have a clogged system if you get no heat at all.

I found that the air temperature thermostat inside the heater box was bad as I get heat when set to HIGH, and some regulated heat if the setting is set to over 85 degrees F. This is a good indication the controller is not giving the proper voltage to the heat valve based on the thermostat feedback.

That are my experiences so far ...
XJ8 Denso Valve shown CLOSED when 12VDC is applied, the valve is otherwise NORMALLY OPEN meaning you get heat with the electrical connector disconnected.
XJ8 Denso Valve shown CLOSED when 12VDC is applied, the valve is NORMALLY OPEN with no voltage applied (Electrical connector disconnected)

 

My friendwill appreciate this discussion thanks

 

This thread helped me out sooo much! Turns out my hoses were routed incorrectly after doing my timing chain tensioners.

 

Great info on this discussion.

 

I think it is such a wealth of information that we have available to us on these excellent but
sophisticated cars. There are so many things that are obscure to the average driver and
may not be as apparent upon initial troubleshooting. Having the copious experiences of
forum members is a treasure and deeply appreciated.