The blower works ok, but heat comes out of the vents inconsistently. Sometimes heats, other times no heat. Does anyone know what may cause this problem?

 

Heater pump going out. Eventually it will quit entirely

Z

 

Is it the small pump located at the firewall where tit's nearly impossible to reach ? ( on Jag kk8 )

 

yes it is. IMHO, The easiest way to remove it is to take out the catalytic converter on the left side. Then you have some room to get it out working from under the car. Jag repair com has the procedure in their procedure listings.

http://www.jagrepair.com/JaguarXK8HeaterPumpValve.htm

mine is out too, so you’re not alone .

Z

 

As your problem is intermittent, it’s possible that your heater valve is sticking. Sometimes just a quick tap with a hammer is enough to release the solenoid.



in my pic, just left of the clear house (I was cleaning out the heater core) you can see the top of the valve body.

Worth a tap as a zero dollar fix. In my case dirty coolant blocked the solenoid valve and heater core.

Later I did a full coolant drain and flush, replacement. Was working fine after that.

Saying that the water pump is always working, so failure is a common problem.

 

Dont jump to conclusions ..it could be the fan on the temp sensor behind the knee pad or bunged up with fluff. ..little slotted vent . I put in a second pump at the top by the expansion tank
Look at my post Heater Inconsistencies. it covers the lot. If you look below under related topics you will see it.

 

Hi o gary,

Probably the first thing to check is your coolant level. Low coolant can cause intermittent heat in the passenger cabin. The low coolant sensors sometimes stick and don't report low coolant.

Cheers,

Don

 

Could be the thermostat. I'd replace that before tearing into the heater pump/valve.

 

DefaultUpdate. Items checked to date and still no heat. I am now questioning if one or more blend door actuators are not working. Does not seem easy to reach to check these out. Looked at all the videos and still not perfectly clear. Apparently have to lay upside down in footwell under steering column to see. I removed the glove box and verified the Recirculating actuator operates properly. No other actuators on passenger side.

1. Drained, flushed and refilled coolant system. Replaced new water pump and thermostat.
2. Pulled the white connector to water valve and still no heat.
3. Tested the continuity of the pump motor with an ohm meter at the black connector terminals at wire end and via the fuse box . All tested fine. Pump was running as we removed the relay. It stopped at that time, relay replaced.
4. Checked all fuses and relays with ohm meter. All are good.
5. Pulled thermister and cleaned. Fan was running on temp sensor
6. All fans are blowing strong, just no heat at all.
7. Finally, after all those items above, I had a shop back flush the heater core and then I started slowly to get some heat. It does not burn you out as some have mentioned but after a few miles, it warms up the cabin enough for my wife who is very cold natured.

 

Double check/replace the kinked hose to the heater core. There are 2 hoses. The problem hose is the one with the one-way valve and that nasty flat/kinked section in it. That kink (supposedly there by design) sometimes collapses and stops/slows the flow to the core. The shop that cleaned your core had to mess with this hose and likely nudged it enough for some flow to go through. To my knowledge, there is a cheap Uro replacement part from the usual online places.

Apparently, that one-way valve is there to prevent the heat from the cooling system to flow back into the core by convection in the summer months. It is probably worth a try to temporarily install a conventional hose instead for debugging purposes. Our cars provide PLENTY of heat to the core.

As you pointed out, the vents/flaps also matter. My car seem to produce the heat the cabin the fastest on recirc and face.

Best of luck, keep us posted.