brandon402

So, I had some issues with my heater and Ive gone through all the steps as far as checking for hot coolant through all the associated hoses, as well as getting my system power flushed. I checked that bypass valve that opens and closes when you switch from hot to cold and that works wonderfully.

My heat, while warmer than it was before i got it power flushed, still just doesnt seem to get as hot as I would think it should. My t stat is brand new btw. I also noticed that, when I drive, its not nearly as warm as when Im sitting still. I have installed a piece of card board in front of my rad at the advice of my roommate, and that seemed to help a bit.

I have also pulled the actual control unit and checked the vacuum hoses in back of it and those appeared to be good to go. So... what next? The blower is blowing, its just the air just isnt that hot. Is there something else I am over looking? Does the temp switch or temp sensor have anything to do with it?

Any advice would be great.

Abovetimberline

What is your actual temp on the guage?mine reads at the halfway point which I assume is 160 or approx and the heater is to hot to run all the time. It is possible the blend door is not closing all the way.
Are both hoses to and from the heater the same temp?

miglia-spyder

I have warm air too. I have a lower T-stat in mine so mine runs at about 185 all day long. This made more of a difference than i thought it would. So i will be putting the 210 T-stat back in.

BTW jeeps run at about 205-215 usually. And straight up on the guage is 210.

djb383

Had our '98 for a couple of weeks now and been doing the R&R. Factory t-stat is 195F and the ScanGauge showed coolant temp ranged from 193F to 201F. I flushed the heater core with the garden hose going in thru the top heater hose and out the water pump (bottom rad hose removed at the water pump). Replaced the 195F t-stat with a 180F and the ScanGauge now reads 181F to 188F and the heater will drive you out. It's my understanding that '98s don't have the heater control valve. I've seen new t-stats malfunction so I always check them on top of the stove in a pan of water using a cooking thermometer. Poor coolant flow thru the heater core and/or malfunctioning t-stat are usually the cause of poor heater performance.

dan lawrence

i was having similar problems and ended up getting a new water pump and flushing the system. my heat works fine now and was a much cheaper alternative then getting a new heater coil!

brandon402

My gauge NEVER gets close to 210 (which is the line thats straight up on the gauge). It always floats between the line to the left of the 210 and the 210. Rough guesstimate would be 195-ish. Which, from what Ive read, is normal operating temp. And yes, both hoses are hot, which is why I dont think its the t-stat.

As for this blend door? What and where is that?

Yea, I definitely agree here, but in my case I have had the core power flushed, the t-stat is new, and I can physically feel the lines to and from the core are hot. So, I really dont think my problem is any of that. However, just like you, ive seen brand new t-stats go bad from the store so Im not totally ruling out the possibility of a bad stat. But, if the stat wasnt opening like it should why would the hoses going to the core BOTH be hot? Wouldnt a closed stat result in cold hoses? And additionally, I do have heat, its just not HOT heat, its room temp warm heat.

golfmiser

Sounds like you may still have air in your coolant.Try bleeding the system completely.

djb383

If you have hot hoses, sounds like the flapper door under the dash isn't fully closing and allowing cold outside air in the mix.

I've had some vehicles that were a bit stubborn to "burp", after a coolant drain/flush/re-fill, but our '98 4.0L was NOT one of them. I filled the rad, started the engine (rad cap off and idling), watched coolant level and added coolant as the level dropped. Once the coolant level begins to rise, install the rad cap before it overflows. Make sure there's plenty of coolant in the overflow bottle and be sure to re-check the coolant level at the rad cap when cold. The best way to make sure the cooling system is full is by removing the rad cap (COLD ENGINE), not by just looking at the overflow bottle. There are two one-way valves in the rad cap. Both must function correctly in order to keep air out of the cooling system AND allow the system to re-fill from the overflow bottle as the engine cools. If one or both valves in the rad cap fails, it can be bad news. Rad caps are cheap, I replace often.

98 JeepJeep

then your heater core is clogged.........or flow is restricted........

brandon402

I agree 100% with what you're saying about properly burping the system using the rad cap. And, if I had a rad cap, I would for sure have done it that way. However, my 89 doesnt have a rad cap, the rad is filled via the overflow bottle.

That flapper door sounds like my next avenue though. I'll check that next.

Thanks everyone for all your suggestions!

djb383

Isn't the principle still the same though?........you fill it at the overflow bottle with the engine idling until the system is full. Our '06 Satun Vue has the pressurized overflow bottle and it's very easy to fill/burp.

brandon402

Well yea, but you were going into great detail about how to do it on a rad cap equiped system. So, it appeared as if you thought my system was like that. But yea, again you're right, its the same thing either way. Just one less cap for me too look at. But, as I said before, I had the system power flushed and they use a pretty nice machine that uses a vacuum setup to get the air out and flush the entire system pretty thoroughly. So I figured that setup removed any air pockets I might have had.

After I dig into the dash and check out that door, I'll know more. Either way, I'll make sure to update this thread with my progress. Thanks again!

brandon402

So, i braved the below zero temps today and dug into my dash a bit today. I think i found that flapper door... Is it the one that is actuated by a sort of vacuum diaphragm? If so, it works and works great. I also found that, when I pushed the controls all the way to MAX i got the most heat. Also, when I put the vent to go to the windshield, that it gets way hotter than when set on hot.

So... again im at a loss. My next move is to replace the t-stat with a lower temp one (thinkin a 160). Other than that.... anyone got any ideas?

chrisl757

My Defrost is way hotter than HEAT or VENT.

Both hoses are hot, I flushed core clean and temps are 210 steady. There should be heat pouring into the floorboard, but it's not.

Because I CAN get hot air on defrost, it makes me think that this has to be some sort of a door issue (which may or may not be a vacuum issue?).

Where did you look to verify your blend door works? I don't know what this looks like, so it is hard to know if it is a piece of foam or fabric that has completely disintegrated.

Thanks for any help. I'd be willing to bet that both of our Jeeps have the same source of trouble.

brandon402

Hell yea, sounds like we are both experiencing the same issue. As for the door, thats what I was hoping I could get verified by someone on here. I found a "door" that was accuated by a vacuum diaphram but im not sure if its the exact one I should be looking for.

It is located right under the passenger side dash. There was a little shield that can be removed by 2 phillips head screws and then there is the door and the diaphram. I verified that it opens and closes depending on the position of the vent control (not the temp control).

Oh, and try this... push the arm completely to the left, not off, but to max and see how much heat comes out. I was amazed how much warmer it was compared to the actual HEAT setting.