I know there's a thread for this but it's pretty old, so I figured I start a new one with the Temps dropping. I'm thinking I have a vaccuum issue somewhere because I only get air flow from the defroster. But that air is also warm at best and far from hot. I found what I think are the heater hoses and followed one coming out of the top of the water pump to a t-intersection with a cap. Continue following that to a 4 way intersection down into the firewall. Followed the return to the same 4 way intersection which then continued on back to the water pump. I put a garden hose to both hoses and both times I pushed antifreeze out of the top of the water pump and no water out of the other hose. Really confused here. And any help would be nice. Any insight on what this inintersections are and what they are for would be great, I have a picture but I'm not sure how to upload it. Thanks guys.

Hot coolant flows from the t-stat cover on the head, to/thru the heater core under the dash, then returns to the water pump on the block. This coolant flow "loop" is the bypass loop. U may have what's called a heater control valve between the motor and heater core. It is known for causing leaks and heater performance problems. Lots of folks have eliminated it......the factory eliminated it on '97 up XJs.

So in theory I could go get all new hose and run it straight amd take out all the garbage in between?

I'm confused also since you don't state your year, engine etc.

Absolutely.......no theory to it. Be sure to plug/cap the vacuum hose. 2 sizes of heater hose.......5/8" and 3/4".

Except we don't know what year he/she has, do we?

And while you're at it flush your heater core both ways with a garden hose.

What's with these people that don't even know WTF they're driving.

I'm going out on a limb/reading between the lines that the OP has a HCV.

That's great.

But, HO and Renix have different hose configurations and they can both have HCVs.

I vote for a software change on CF that allows no posting without signature filled out with at least year!!

Brilliant!.......that's why u da man.


Can the HCV be eliminated on Renix as well?

Absolutely, but the configuration is different because of the expansion bottle.

We will just have to lay in the bushes & wait 'til he comes back on to pin him down on what year he's dealing with..

So as long as the configuration of the bottle plumbing is kept intact, the HCV can be eliminated using 5/8" and 3/4" heater hoses in the proper lengths, right?

Yes. Like this: