XJ XJ8 / XJR ( X308 ) 1997 - 2003

How to test for a bad water pump?

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  #21  
Old 01-20-2018, 08:20 AM
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Yes, I checked for bubbles on yesterday's cold start. There were none, which surprised me. So you think that it's not worth getting a cooling system check on the car? What about one of those tests that uses a blue dye to see if you have combustion gasses in the coolant?

No white smoke, or sweet smelling exhaust.
 
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Old 01-20-2018, 09:39 AM
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Sounds like it may have burped finally?....I'd monitor it for a few more days.
 
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Old 01-20-2018, 10:14 AM
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Originally Posted by Highhorse
Sounds like it may have burped finally?....I'd monitor it for a few more days.
I'm guessing that is the case, at least for the time being. I was FINALLY able to get a coolant reading. Using dash command. But it only let you log for 30 minutes. I'll buy it, so I can read coolant all day. It does work with my ELM obd2. Highest I saw the temp get up to was 203 Fahrenheit. In the city, not highway. What is the halfway point on these cars?

Then I had another 5 minutes drive to get back home. And the fans kicked on for 2 minutes, then shutoff. It is 59 degrees Fahrenheit at the moment, ambient.
 
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Old 01-26-2018, 01:52 PM
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Was off today, so had time to mess with the 308. I checked the coolant reservoir again for bubbles. There were none. That was on a cold start.

Driving in stop and go city traffic, the temp went as high as 221 fahrenheit which scared me. Moving, the temp comes down quick. So I kinda hauled azz back home to keep temps down. And it worked. BTW, damn this car is pretty quick. Trans kick down is way more responsive to throttle position in sport. Made me miss my dad's XJR lol.

When I got back home, I let the car idle for a bit. When it got to 210 fahrenheit, I popped the hood to see if the fans were coming on. They weren't coming on. So I let it idle a bit longer. When it was reading 217 degrees fahrenheit, the fans were still not on. This is with the AC off, if that matters. So at that point, I shut the car off. Weird thing was, the fans didn't come off after turning the car off.

Any ideas?
 
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Old 01-26-2018, 03:56 PM
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Need to meter the temp sensor and check the wiring all the way to the fans.
 
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Old 01-26-2018, 04:17 PM
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Originally Posted by Highhorse
Need to meter the temp sensor and check the wiring all the way to the fans.
What do you mean by "meter the temp sensor"? I can and will check the wiring to the fans.
 
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Old 01-26-2018, 05:52 PM
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Just did some diagnosing on the car. I read that fans should turn on at 205(96 Celsius) is that true? Mine did not turn on at that temp.

With the AC blowing cold, the lower left fan was turning on and off. Keeping the temps below 210 Fahrenheit. Although this was with my car in the driveway. The upper right fan was not on. Should they both be running with the AC on?
 
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Old 01-26-2018, 08:15 PM
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For the switch check, no its not a Jag, but your measuring resistance, I'm not keen on the paper clips, I prefer a shielded wire, but you get the idea...
For the fans, you should be able to use a 12v source to activate the fans to check function. Obviously you know the one works, I'm pretty sure with the climate system engaged, both are supposed to be operative to maintain temp.
 

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  #29  
Old 01-26-2018, 10:20 PM
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Both fans should always run together. The fans will kick on HIGH when the aircon compressor is engaged (and some other conditions maybe, if coolant is above 40c or something to do with ambient temp, don't recall for sure but it's in the climate control documentation somewhere). They will kick on LOW when the coolant is slightly above the nominal operating temp (and AC compressor isn't engaged), and HIGH if the coolant temp gets a certain amount above that. LOW just runs the fans in series to run each at 6v, so if you have an open circuit in one motor you may only get HIGH operation.

The motors do give out sometimes, I had a dead one when I got my car. It could also be a wiring fault going to the fan. It's pretty easy to remove the fan shroud and test each motor independently.
 
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  #30  
Old 01-27-2018, 09:20 AM
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Originally Posted by Highhorse
For the switch check, no its not a Jag, but your measuring resistance, I'm not keen on the paper clips, I prefer a shielded wire, but you get the idea... https://www.youtube.com/watch?v=zIMjsrOvCqU
For the fans, you should be able to use a 12v source to activate the fans to check function. Obviously you know the one works, I'm pretty sure with the climate system engaged, both are supposed to be operative to maintain temp.
Got it. Will check it.
Originally Posted by nilanium
Both fans should always run together. The fans will kick on HIGH when the aircon compressor is engaged (and some other conditions maybe, if coolant is above 40c or something to do with ambient temp, don't recall for sure but it's in the climate control documentation somewhere). They will kick on LOW when the coolant is slightly above the nominal operating temp (and AC compressor isn't engaged), and HIGH if the coolant temp gets a certain amount above that. LOW just runs the fans in series to run each at 6v, so if you have an open circuit in one motor you may only get HIGH operation.

The motors do give out sometimes, I had a dead one when I got my car. It could also be a wiring fault going to the fan. It's pretty easy to remove the fan shroud and test each motor independently.
I'll start checking stuff in a bit.
 
  #31  
Old 01-28-2018, 09:40 PM
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Well I was busy helping remodel my mom's house. Didn't get to do much. I did find out the #12 and #14 fan fuses are good.

I saw two relays to the left of the fan shroud, or behind the left side headlights. Thought they were the cooling fan relays. However I googled the part number on those relays, and it said fuel pump relay. Does anyone know where the fan relays are? Yes, I know I need to make sure both motors work.

I'm sure the lower left fan motor works, as it was running with the AC on.
 
  #32  
Old 01-29-2018, 06:49 AM
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Here, this will help you with this and other future endeavors.... http://www.jagrepair.com/images/AutoRepairPhotos/jagxj1999.pdf ...dowload it and/or bookmark it.
 
  #33  
Old 01-29-2018, 08:19 AM
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Originally Posted by Highhorse
Here, this will help you with this and other future endeavors.... http://www.jagrepair.com/images/AutoRepairPhotos/jagxj1999.pdf ...dowload it and/or bookmark it.
Thanks!
 
  #34  
Old 01-29-2018, 04:05 PM
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Found some new info just now. But since it went from water pump to cooling fans, I'm starting a new thread. Hope that is ok.
 
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