cruiser54 Posted December 9, 2020 Share Posted December 9, 2020 I have had catastrophic failures of HCVs. Likely one of the reasons for my hate of them. When they split apart driving down the road, MASSIVE coolant loss that could lead to engine damage. Not worth it.... Here's my favorite. Gonna do an oil change on my wife's xJ. Good and warm!! as I'm removing the oil filter, my arm touches the heater hose or HCV and it explodes!! Covers my left arm and my face with 208* coolant!! That's with a factory valve. I'm sure the available replacement valves are worse..... Link to comment Share on other sites More sharing options...
Manche757 Posted December 9, 2020 Author Share Posted December 9, 2020 2 minutes ago, cruiser54 said: Here's my favorite. Gonna do an oil change on my wife's xJ. Good and warm!! as I'm removing the oil filter, my arm touches the heater hose or HCV and it explodes!! Covers my left arm and my face with 208* coolant!! That's with a factory valve. I'm sure the available replacement valves are worse..... That makes a believer out of me. I had the mechanic replace the HCV even though it was not malfunctioning but probably original. I asked him about A Mopar one and he said that some of those made later might be better. Link to comment Share on other sites More sharing options...
Manche757 Posted December 9, 2020 Author Share Posted December 9, 2020 17 minutes ago, Minuit said: I went through the FSM quickly to see if I could find an acceptable spec for vent temperatures and came up short, but if there was a spec I would expect 140 to be within that spec, especially on a very cold day. In my mind, 140 is roughly where "good heat" starts, and I personally wouldn't call 140 "lukewarm" either, so there may very well be something else going on here. Like I said, it'd be best if you could collect your own measurements of the vent temps and report back. Maybe I have less of an issue that I thought. Less heat than in most cars though Link to comment Share on other sites More sharing options...
Manche757 Posted December 10, 2020 Author Share Posted December 10, 2020 On 12/9/2020 at 7:20 AM, cruiser54 said: I can't imagine the heater core is that dirty and it would happen that fast. Hold your hand on each of the heater hoses at the firewall. Same temp? either side of the HCV. How do they compare? If you have an IR gun, use that. But, your hands will likely tell the story. The intake and discharge hoses at the firewall feel to be about the same temperature. The hoses on each side of the HCV feel to be about the same temperature also. I ran across this picture. I guess an AZ plumber had some left over copper. Link to comment Share on other sites More sharing options...
cruiser54 Posted December 11, 2020 Share Posted December 11, 2020 So now we're getting somewhere. I'm gonna bet the blend door under the passenger dash is out of adjustment, allowing cool air to mix with the hot air. Link to comment Share on other sites More sharing options...
Manche757 Posted December 11, 2020 Author Share Posted December 11, 2020 On 12/6/2020 at 3:51 PM, jdog said: Either the blend door isn't opening all the way ... Link to comment Share on other sites More sharing options...
Manche757 Posted December 11, 2020 Author Share Posted December 11, 2020 On 12/6/2020 at 5:31 PM, Strokermjcomanche said: ... it has something to do with your blend door Link to comment Share on other sites More sharing options...
Manche757 Posted December 11, 2020 Author Share Posted December 11, 2020 19 minutes ago, cruiser54 said: I'm gonna bet the blend door under the passenger dash is out of adjustment, allowing cool air to mix with the hot air. Link to comment Share on other sites More sharing options...
Manche757 Posted December 11, 2020 Author Share Posted December 11, 2020 Cool air from outside? If the blend door, it will also negatively impact the ac? Link to comment Share on other sites More sharing options...
cruiser54 Posted December 11, 2020 Share Posted December 11, 2020 Depends. Poke your noggin under the passenger side dash and move the Heat/Cold back and forth. Should be obvious. Link to comment Share on other sites More sharing options...
Manche757 Posted December 12, 2020 Author Share Posted December 12, 2020 I spoke with the mechanic who has done all the work on my 2 MJs. He said he checked the blend doors and found them to be ok. He said one of the hoses going to the heater core was very hot and the other was not. (A change from what I had stated.) He also said that even though the new heater core was installed only a year and half ago, the flushing of the radiator and engine was very rusty. He spoke of working on an XJ recently with a heater core he had installed about 5 years earlier and was filled with rust. I will take the truck back Tuesday for him to disconnect hoses and flush the core. I also asked him after he flushes it to attached short pieces of heater hose to the heater core and turn them up and fill the core with a rust dissolvent and leave it for a day and flush it again. Link to comment Share on other sites More sharing options...
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