Heating problem. I'm stumped!

Alright...so over the summer I performed a bunch of maintenance on the cooling system. I was overheating so I changed out the radiator, the water pump (a chinese star was left!), thermostat and serp belt.

Now, I am getting no heat. She won't even heat to 210. 190 if I'm lucky. I replaced the thermo again...with another 195 deg. Still, not enough heat. I flushed through the heater core only until it ran clear so I know I have passage through that. The blend door is operating properly. I added water since I may have the wrong mixture...still nothing. I placed cardboard in front of the radiator, still nothing.

I am running catless...could this not be creating enough back pressure to heat up the engine?

I have not checked to see if the heater core fins are gummed up, and I have not checked the tension on the serp belt since I installed it. I do get an occasional squeal when I turn on the defroster. Not sure if that is the AC clutch, or the belt.

Anyone have any thoughts?

Oh yeah...this is a 99 with the 4.0...woops

What gasket did you use with the thermostat? A generic one, universal style gasket, one style fits all, you just punch out the right holes or the OEM type especially made for an XJ; 4.0 for your year (there are some changes in the thermostat housings over the years).
Having the wrong gasket in there can cause all sorts of heater grief and cause the thermostat to function poorly.
The heater outlet (which can be blocked with the wrong gasket) on the thermostat housing, as well as being for the heater, is also a bypass for the thermostat. Without the bypass you can have cooler water (coolant) near the thermo with very hot water (coolant) stacking up behind it, well away from the thermostat.
Maybe disconnect the heater inlet and outlet as far away from the heater as practical and blow through there. I know it sounds gross, but is actually a common troubleshooting method. I've found numerous partial stoppages in everything from fuel lines, through the heater to tranny coolers and tranny cooler lines using this method.
It's also possible on some model XJ's to put the thermostat in bassackwards. Though this usually results in very high temps in the older models, in the newer models this can trap cooler coolant close to the temperature gage sender. The tip off is usually wild swings in motor temperature. The thermo eventually opens all at once eventually and not a more gradual process like it should be. The process can Sometimes be similar with air blockages (cold, cold, cold, way too hot).

What about feeling the heater hoses after the engine is hot? If the hoses don't get hot, you have no coolant flow through the heater core. If both inlet and outlet hoses are hot, you have no airflow through the air side of the heater core.

winterbeater said:

What about feeling the heater hoses after the engine is hot? If the hoses don't get hot, you have no coolant flow through the heater core. If both inlet and outlet hoses are hot, you have no airflow through the air side of the heater core.

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Don't be timid just wrap your lips around that black nasty hose and blow.

Good idea though.

LOL 8mud! The top heater hose gets hot, the bottom does not. It almost feels like the top hose gets hot from heat transfer, more than hot coolant. I would think that if I take the cap off the flush adapter, I would get shot with coolant, but I don't.

I haven't paid any attention to the gasket. I always just asked for the gasket for the 99 with 4-oh

bhansen99xj said:

Alright...so over the summer I performed a bunch of maintenance on the cooling system. I was overheating so I changed out the radiator, the water pump (a chinese star was left!), thermostat and serp belt.

Now, I am getting no heat. She won't even heat to 210. 190 if I'm lucky. I replaced the thermo again...with another 195 deg. Still, not enough heat. I flushed through the heater core only until it ran clear so I know I have passage through that. The blend door is operating properly. I added water since I may have the wrong mixture...still nothing. I placed cardboard in front of the radiator, still nothing.

I am running catless...could this not be creating enough back pressure to heat up the engine?

I have not checked to see if the heater core fins are gummed up, and I have not checked the tension on the serp belt since I installed it. I do get an occasional squeal when I turn on the defroster. Not sure if that is the AC clutch, or the belt.


Anyone have any thoughts?

Click to expand...

Your coolent temp is fine. Check the valve that controls the coolent flow to the heater core. There is a butterfly valve inside that opens and closes with the lever on the outside. (I'm in Iraq, so I can't look at my 95 XJ and see if cable or vacuum operated, NAPA shows it to be vacuum) If the butterfly breaks loose from the shaft inside the valve, it can stick in the closed position while the lever moves on the outside. The valve will always pass a small amount coolent to aid in purging air from the system, causing one hose to be hot and the other to be cold. Have someone move the temp lever on the dash while you check the valve for movement before pull the hose off. (NAPA part #BK 6601272 for 95 XJ)http://www.napaonline.com/masterpag...K&PartNumber=6601272&Description=Heater+Valve

Defrost mode will cause the A/C to cycle on and off to dehumidify the air. Check your belt tension to the A/C.

lol I was hoping this wasn't something inside the dash. I'll check it out tonight at work if it is slow and I have time. I am going to check out the blend door while I am at it. It looked fine before, but then again I never ripped it apart. I just watched the actuator move.

I re read my post, when I said silicon, I meant silicon lubricant, the kind made for your door and window rubber. Just wanted to be clear.:dunce:
It helps soften the belt up some.

cf_collins said:

Check the valve that controls the coolent flow to the heater core

Click to expand...

There is no heater control valve on a 99. I believe 96 was the last year for that POS.

birchlakeXJ said:

There is no heater control valve on a 99. I believe 96 was the last year for that POS.

Click to expand...

Guess I won't be checking that then! Shows what I know

So, after the engine is hot, you take the flush adapter off (while it's running) and don't get sprayed with coolant? If so, somehow ???????? that hose is blocked off and nothing is flowing thru the heater circuit.

OK, I checked in the FSM and looked at picture of the thermostat gasket. It should have a teardropshaped slot adjacent to the big hole in the middle. High liklihood (best guess) is that you don't have the correct gasket in there which would block the coolant flow to the heater like 8Mud said.

Try back flushing heater core with a garden hose if it's not the gasket. I've had this problem with both my 1990 & 1987. On mine I took the hoses off & flushed the core. Got a whole bunch of crud out of the core & had heat again. One word of caution, if the core is weakened from corrosion it could blow out. Try to use the least amount of pressure when doing this as garden hose water pressure can be 40# or higher. I have done this on a number of vehicles over the years & I've only blown up one heater core in a Chevy Blazer & that core was rotted out so I had to replace it anyway.

A little update...I attempted adjusting the belt tension and busted off the last 2" of the long tensioner bolt. Needless to say, I made the squealing worse when running the ac/defroster.

I have yet to take a look at the gasket. I will as soon as she cools down a bit.

Still running less than 210 with little to no heat though. I took the cap off the flush adapter on the upper heater hose and there was very little flow. Just enough to bubble up a little bit. My rad cap is cool to the touch as well. This stuff is beginning to make no sense to me. 18 degrees on my way home from work this morning with no heat...it is only going to get worse!

winterbeater said:

OK, I checked in the FSM and looked at picture of the thermostat gasket. It should have a teardropshaped slot adjacent to the big hole in the middle. High liklihood (best guess) is that you don't have the correct gasket in there which would block the coolant flow to the heater like 8Mud said.

Click to expand...

I did this about a week or so ago. I did get some sludge before it ran clear, but it did run clear. This was with minimal pressure so there shouldn't be any damage to the core.

bhansen99xj said:

Still running less than 210

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If it's over 180 at 18 outside, I would say you are fine on the engine temp. I've never had any cooling/heating problems my jeeps, so I've never torn in them. Just worn out tires on two of them and none working electric door locks on one.

http://cgi.ebay.com/ebaymotors/Part...kparms=72:543|65:12|39:1|240:1318#ht_1821wt_0 found this on ebay and was wondering if you had tried taking the motor that actuates the blend door off and turning the axle it is mounted on to make sure that it is not snapped off in there somewhere and stuck blocking your heat. if its broken off just because the motor still moves doesn't mean that the door is moving. i'm having problems with lukewarm heat at best in my '00. flushed the heater core and all that still not great so i'm going to take the blend door motor off next and see about it for myself. doubt that kit is worth it though but who knows.