Mysterious coolant leak

[mancheflo]

So I have this mysterious coolant leak going on and it just happened out of the blue, backed the truck up to unload some stuff 20 minutes later I notice this big puddle of fluid, I go look at it and it’s definitely coolant leaking but the reason it’s mysterious is that it’s leaking from the middle left part of the engine bay near the reservoir tank but the outside of the tank and near where it’s bolted in doesn’t seem to have any fluid on it but In the second picture I circled where there is some coolant but I’m not sure about it at all,

[mancheflo]

And I haven’t ran it since Friday and this morning there was more fluid on the ground 

[jeeptec1]

That is the heater control valve leaking. I have replaced many of those. They become brittle from constant heating and cooling of the engine. Easy to replace.


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[yxmj]

Or it can be taken out altogether.... And it will never leak

 

 

[mancheflo]

1 hour ago, jeeptec1 said:

That is the heater control valve leaking. I have replaced many of those. They become brittle from constant heating and cooling of the engine. Easy to replace.


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That’ll cause it to leak that much and even when it’s not been ran?

[jeeptec1]

That’ll cause it to leak that much and even when it’s not been ran?

Yes coolant flows through the valve when heater is on. And is bypassed externally but will always have coolant in it. It will leak under pressure when running. Will drip when off.


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[mancheflo]

5 minutes ago, jeeptec1 said:

Yes coolant flows through the valve when heater is on. And is bypassed externally but will always have coolant in it. It will leak under pressure when running. Will drip when off.


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Alright well hopefully that’s it! Thanks man

[Minuit]

Its purpose is to reduce AC vent temperature by 3-7 degrees when the temperature selector is pushed all the way to "cold" - if you don't care about that, delete the valve. Otherwise, replace it. The Mopar valve is still available.

[AZJeff]

The later XJ’s were plumbed from the factory without the heater control valve, and I never noticed poor AC performance because of it, and I live in Phoenix.

 

if I had an XJ or MJ with a leaky valve, I would delete it.

[Minuit]

4 hours ago, AZJeff said:

The later XJ’s were plumbed from the factory without the heater control valve, and I never noticed poor AC performance because of it, and I live in Phoenix.

 

if I had an XJ or MJ with a leaky valve, I would delete it.

I wonder if the HVAC box in '97+ XJs have different routing compared to the earlier models, or if Chrysler just decided to eliminate a couple of bucks and a potential failure point at the cost of some A/C performance.

 

On the '96 and older HVAC setup, air that has already been cooled by the evaporator flows right past the heater core (separated by some plastic, but still) no matter what the blend door position. The A/C can be performing perfectly, but it's no good if that ice cold air gets warmed up again by the piping hot heater core ducting.

 

I'm not @$$-pulling the 3-7 degree number, by the way. That's from my own testing. That was a big enough difference for me to un-delete my heater control valve. That's not enough to turn a well-performing system into a poorly performing one, but it does make a difference.

[schardein]

1 hour ago, Minuit said:

I wonder if the HVAC box in '97+ XJs have different routing compared to the earlier models, or if Chrysler just decided to eliminate a couple of bucks and a potential failure point at the cost of some A/C performance.

 

On the '96 and older HVAC setup, air that has already been cooled by the evaporator flows right past the heater core (separated by some plastic, but still) no matter what the blend door position. The A/C can be performing perfectly, but it's no good if that ice cold air gets warmed up again by the piping hot heater core ducting.

 

I'm not @$$-pulling the 3-7 degree number, by the way. That's from my own testing. That was a big enough difference for me to un-delete my heater control valve. That's not enough to turn a well-performing system into a poorly performing one, but it does make a difference.

I deleted the valve on both my XJ and MJ.  Later, I completely went through my AC, but was underwhelmed with the results (on both).  They do ok on max setting.  I agree that an additional 7 degree  reduction is significant.    

[AZJeff]

10 hours ago, Minuit said:

I wonder if the HVAC box in '97+ XJs have different routing compared to the earlier models, or if Chrysler just decided to eliminate a couple of bucks and a potential failure point at the cost of some A/C performance.

 

On the '96 and older HVAC setup, air that has already been cooled by the evaporator flows right past the heater core (separated by some plastic, but still) no matter what the blend door position. The A/C can be performing perfectly, but it's no good if that ice cold air gets warmed up again by the piping hot heater core ducting.

 

I'm not @$$-pulling the 3-7 degree number, by the way. That's from my own testing. That was a big enough difference for me to un-delete my heater control valve. That's not enough to turn a well-performing system into a poorly performing one, but it does make a difference.

Interesting.   What's most notable is that, for the most part, I cannot think of any modern cars that have a water shutoff valve for the heater core.   It's like the auto manufacturers figure it's not worth the hassle (probably more likely the cost) of adding in that device for the small difference.

 

I kinda wonder if my old 2000 XJ (or my current MJ with 2001 dash) had sported a heater valve if it would have been more efficient.   I guess if I REALLY want to get motivated, I can temporarily bypass the core and do some measuring.   Maybe this summer.....

[Ωhm]

Maybe HVAC plenum design has something to do with heater core valve or no heater core valve.

[AZJeff]

7 hours ago, Ωhm said:

Maybe HVAC plenum design has something to do with heater core valve or no heater core valve.

Perhaps.  I have detailed photos of a disassembled 97+ XJ heater box.  If someone has photos os a disassembled pre-97 XJ/MJ heater box, I would be glad to compare them.

[cruiser54]

I've never noticed a difference using an AC vent thermometer before and after deletion and I live in Arizona.

 

So, what is more uncomfortable?

 

POSSIBLY, but not probably having higher AC vent temps, or sitting alongside the road on a hot and humid day with an exploded heater control valve?

 

And that's what they tend to do. Come apart unexpectedly and nearly empty your cooling system before you know it.......

[Minuit]

20 hours ago, cruiser54 said:

I've never noticed a difference using an AC vent thermometer before and after deletion and I live in Arizona.

And I have noticed a difference. On two back-to-back days, in virtually identical conditions, driving the same route at the same time of day on the same A/C setting.

 

I encourage everyone interested in this subject to try it for themselves. Bypass the heater core (that's pretty much what the heater valve is - a switchable heater core bypass) and tell me if your vent temps go down any. Without any more data, it's your word against mine.

 

Yup, it's a potential failure point. Yup, it's 4 more hose connections. On my truck, it makes the A/C work better. I really like it when my A/C works better. Everything is a trade-off.

[cruiser54]

Always make sure the heater door is closing completely!!

 

Now, when it comes to one guy's experience to anothers....

 

I've done this on at least 10 vehicles.......