Cold bottom radiator hose - where to start?

Wife brought to my attention that her 08 KK has no heat. Checked blend door actuator, was fine. Started checking hoses - at normal running temperature:
1. top radiator hose is hot
2. bottom radiator hose is cold
3. hoses running to heater core are warm
4. radiator cap is cold, and can be removed with no problem
5. coolant under radiator cap is cold
6. overflow tank is empty

Please note that this no heat issue has been present for a few weeks, and during that time the vehicle has not run hot whatsoever during its use as a daily driver (40 miles per day) nor during longer weekend trips.

Any input on where to start will be greatly appreciated. Thank you.

Update...

After playing around with it running while the radiator cap was off, I took it for a ride. During the ride, I turned the heat on, and it blew fairly hot for abut 30 seconds then went cold. After turning the heat off for a while and turning it back on it did the same thing.

When I got back, I noticed the following:
1. top radiator hose was hot
2. bottom radiator hose was fairly warm
3. hoses to heater core were much warmer than before
4. radiator cap was cold, but there was some spray from the cap when opened
5. coolant under the cap was much warmer, but still not hot.
6. overflow tank still empty

I'm assuming the rad was filled when you removed the cap? Fill overflow tank. replace cap with new one. See if that helps. May have pulled in air or next, maybe thermostat stuck.

I assume the radiator was filled, as there was coolant under the cap.

I left it idle for awhile with the cap off, and now the bottom hose is hot to the touch, as are the heater core hoses. Heat is running consistently luke-warm.

Replace the cap anyway. May have worked air out. Make sure you top off the overflow tank (HOAT only) or you may suck more air in as the coolant in the system contracts as it cools.

Ok, not sure what I am missing here. I seemed to make a tiny bit of headway yesterday but not enough to justify the amount of time spent.

I topped off the radiator and let it idle for about 30 minutes with the cap off and the bleed screw partially backed out. level in radiator did not go down and I didn't see any bubbles coming up as I did yesterday.

When I shut it off the top hose was hot, the bottom hose was cold, the hoses going to the heater core were warm and I still have very little heat in the cabin.

going off my recent experience with a different vehicle.
stuck thermostat or bad waterpump

uss2defiant said:

going off my recent experience with a different vehicle.
stuck thermostat or bad waterpump

Click to expand...

My initial thoughts as well - but wouldn't either of these cause an overheating issue?

Frank R said:

My initial thoughts as well - but wouldn't either of these cause an overheating issue?

Click to expand...

Like uss2defiant said, probably the tstat or WP. Tstat is easy but WP not so much. I'd still make sure it's not just air in the system.

Why it isn't overheating? Maybe you caught it just in time. Some component in the system could be in the process of failing so maybe Tstat is partially opening sometimes.

How long did you run it with nothing in the reservoir? I'm assuming the KK tstat has the bleed port like the KJs. This will let some circulate. You asked where to start so I told you what I would do. I like to go easy to difficult.

Seems like poor circulation so maybe air lock from low reservoir level OR tstat OR WP. Not a KK owner but KJs are really sensitive to air especially in the heater core which would cause your no heat issue. Maybe you continued to add to this air issue by not filling reservoir? Now no visible flow and still cold bottom hose makes me think Tstat (easy) or last resort water pump (PITA).

All of this could still just be air in the system. Air is much more compressible that coolant so air could cause the low pressure when you did run it for a bit when full OR maybe bad cap adding to the issue.

again going off my recent experience with a difference vehicle, you may not be running the vehicle long enough to see it overheat.

I was able to diagnose a bad thermostat and/or water pump on that vehicle by using a clear tubing to see if there was flow. The reason why I did so was the inlet heater hose was getting hot but the return heater hose was warm/cold.

So I replaced both and that solved the problem.

I have found that using a coolant pressure tester helps with getting some of the air out of the system. IMHO.

Usually if it's a bad WP you'll have noise and/or a leak. Plus at higher RPMs you'd get more heat. To me it sounds like a Tstat that's stuck largely open. Where does the gauge read? Although the gauges have a big range, I suspect even if it's running cool it'd probably read about normal. It has to really get stuck to trigger a code. You can get an OBDII scanner and see what it's running at - should be 200-220 usually.

Also, KKs have an open cooling system (radiator cap on the radiator, the coolant take just has a plastic cap on it), which self bleeds so I doubt there's air in it.

except in my extreme case, it was a just over a year old WP.
there was no noise, no leaks and the impeller wasn't spinning with the pulley.

Got it. Did it have less resistance when spun by hand? How did you diagnose it?

I really appreciate the guidance thus far.

Its been run daily a minimum of 20 miles each direction, and several times on longer trips over 100 miles each direction during this time. The temp gauge has never gone higher than midpoint.

To swap out the t-stat, do I need to do a complete coolant drain, or just catch what runs out when I remove the housing?

I assume the system will need to be bled again once I replace the t-stat - what is the correct/best way to do this? I've read several methods, but it's obvious that what I have been doing isn't necessarily working so well.

either from the radiator petcock or just unbolt the housing.
you could save some coolant with a hose clamp and clamp the lower radiator hose if it doesn't have the spring in it.

The best is to unbolt the hex bolt by the upper radiator hose and fill coolant from there.
Run the engine and bleed air from there.

Should the bleeder bolt be removed completely or just loosened for bleeding?

unbolt to fill then loosely tighten for the air to bleed with engine running.

So here is where I am at:

Replaced the thermostat yesterday, however the old one tested fine. Let it run with the bleeder cracked for about an hour. At this time, the top and bottom radiator hoses were hot, but the hoses going to the heater core were warm at best. No detectable heat in the cabin whatsoever. Took it for an extended ride, no change in heat output at higher RPMs, and temp gauge never went above midpoint.

Looking at flushing the heater core today, unless somebody has a better idea. Can anyone tell me which hose is the inlet and which is outlet?

Not sure what the heater hose route looks like on a KK but the water pump and I think timing cover on the KK and KJ are the same. The hose that comes off the timing cover higher and closer to the water pump carries coolant to the heater core inlet. Maybe you can trace that back to the firewall.

Edit: Don't think I'm explaining this well so I'm trying to attache a diagram but not sure if its working.