Need help with heater system

I have a 1988 MJ. I changed out the closed system to the open cooling system. I also changed out my gauge's and couldn't get the temp gauge to work so I installed an aftermarket one.
Here is my problem. Whenever I start my vehicle and it gets warmed up my heat takes forever to get hot. Sometimes it gets hot and then comes out cool again. The jeep is running pretty cool as well. Temp says 180-200 most of the time. The thermostat was replaced when I changed the system. I noticed that if I get on the highway and put it in 3rd gear(I am on 33's with 3.55's) that the heat starts working great. In fact, it usually stays working good after this. So, it seems to be something about running higher RPM's is helping. Anyone have any thoughts.

I also wanted to add that everytime I shut my jeep off I can hear the coolant going into the resevoir which is located right next to the radiator cap. There is plenty of coolant in there though. It is weird how you can hear it. Almost like it is boiling or letting air out.

Heat in drive, cool at idle, is pretty common problem. Possible causes are an air bubble, blend door, water pump vanes (not much fluid circulates at idle in the first place), clogged heater core (low heat transfer at low pressure), and so forth. The fact that the temperature gauge also shows low indicates to me that you probably have an air pocket. Backflush the radiator, heater pipes, and block, then refill with heater on full blast, and bleed

Okay. I have thought it might need a good flush. I did blow out the core with an air compressor, but maybe I loosened up a bunch of junk and its clogged again.

My one question is how do you bleed an open system? On my closed one I would take the heat temp sensor off from the back of the block and fill it on a hill until coolant came out.

This is how I do a full fill after flushing. Make sure the heater is running full blast so that the valve and core are unrestricted. Add 1 gallon of green coolant and 1 gallon of distilled water ($2 at any grocery) to the radiator, add more coolant until radiator is full, then add coolant to the FULL line on the overflow bottle. If you have a temp sender at the back of the head you can keep it loose during the fill to allow air out, although I typically use the sensor in the thermostat housing since it's higher up (I don't believe you have that though). Once it's full, run the engine with heater on full to allow everything to circulate. The coolant will drop when thermostat opens up and as air is evacuated, so add more green coolant as needed to keep the overflow bottle between the two lines.

Okay, that makes sense. Your right about not having the sensor at the t-stat housing. So, after you add that one gallon of water you don't add anymore water? Or is the coolant you mentioned adding after the water already 50/50? I just want to make sure I am not assuming anything. Last time I did the job I did a complete 50/50 mix.

just add coolant after the water, you will probably have some old stuff still in the engine so you want to make sure to end up on the 60/40 side of 50/50

mbogosia said:

My one question is how do you bleed an open system?

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It's an OPEN system and should "self bleed" after a few drive cycles. That's why you hear coolant going into you ovwerflow. when coolant expands it pushes into the overflow (along with any trapped air). When it cools, it suck coolant back in (without air).

On the gauge question: If you swapped a full gauge cluster (as opposed to idiot lights) you'd need a different sender.

T-stat: Is it a 195F stat??

Heater core: Flush the core independently of the rest of the system, flush, back flush, flush, back flush (with water). It's a plumbing system. The only thing you'll get out of there with compressed air is dust, and may even blow a hole in the core (I said "may")

I think I know what may be the problem. My hose that connects to the reservoir didn't want to seem to fit snuggly when I first put it on. It was an old hose I grabbed at the junkyard. I didn't think it was a big deal and just clamped it down the best I could. Well, now when we talk of it sucking coolant back in after it bleeds itself I wonder if it is sucking air where the hose connects to the reservoir? I might try to replace this and see if that helps.

Okay, I just pulled the hose that goes to the reservoir and the end was clogged bad. It looked like the rubber inside the hose had deteriorated. I cut the end that was clogged off and the rest seems okay. I blew air through it and it was fine so I am going to see if this helps.

yeah those hoses fill up with dried fluid and clog up like the rest of the system, another thing is don't tighten it too much or it will collapse the nipple

Okay, it already seems much better after cutting off that clogged end of the hose. Heat actually got real hot on a short ride to the car wash. I know it needs to bleed some air out still so hopefully with the hose now sealed it will. Thanks for everyones help.