Hissing after engine is turned off

Im hearing a hissing noise coming I believe the radiator... I'm having all sorts of issues right now with the system and I'm completely green when it comes to cooling.

My issues:
- heat takes forever inside the cab
- hissing sound
- noticing small ammounts of coolant leak

I want to revamp the whole system as I do a fair bit of driving in the mountains and climbing hills taxes the cooling system quite a bit.

What should I replace to make this systems bullet-proof?

Water pump - get a good quality one, and not remanufactured
Radiator - again, as good quality as you can afford
Thermostat - Stant SuperStat Premium 195 degree
Thermostat housing gasket - fel-pro makes a good one
Radiator cap - 16psi iirc, don't buy the cheap junky one AZ has, mine broke when I tried to put it on

While you're in there you might as well replace the lower hose (get one with a coiled spring in it to avoid it collapsing under load), the heater outlet tube on the water pump (you will probably mangle your old one trying to remove it, it's Dorman part number 56398 at least for a '91, under 7 dollars), and probably the heater control valve if you have one and it hasn't been done recently, they are plastic and after a decade in contact with hot coolant they break if you look at them funny.

Year?
Motor?
Mileage?

Bullet proof? - No - Better, yes!
More info needed.

Sry, 1999 XJ, 4.0L, 160,000 kms (100,000 miles)

I also noticed that there is a hose that comes out on the lower passenger side of the firewall in the engine bay and it is constantly shooting air? Is this normal? I've never noticed it before... I can snap a pic later if it helps.

That little hose contols the amount of hot coolant going into your cabin, if i'm think of the right one. It plugs into the valve thingy(forget the name) that has 4 hoses attached to it. This is your vacuum leak aka hissing and reason you dont have heat

heater control valve, probably.

What size hose is "shooting air"? If it's just by sound it could be a vac leak like lowicz96 said, if it's actually blowing air out, it's probably a leak in the AC system or... heck I dunno.

No, the hose terminates in the engine bay and is just streaming air. I'll get a pic in the next hour. It looks very unatural.

No HCV on a 99. There is only one hose on my 97 that goes into the firewall (small flexible hose for the blend door), but the vacuum lines and some of the emissions lines run on the passenger side. A pic would be very helpful.

Only things I can think of are maybe a severely broken AC refrigerant line, and the compressor is blowing air now (very unlikely due to pressure switches), or perhaps the condensation drain line on the HVAC box?

Guessing vacuum or AC leak, but some details here (how long it hisses, is it only when off, does it smell like gas, is it cold, is it hot, does it stop after a few minutes, etc) would help. There are something like 4 vacuum lines, the 2 lines on the purge solenoid, 2 on the can, 1 to the vac can, the AC lines, the blend door line- surely there's something that looks like it should be plugged in?

The hissing you are hearing after the engine is turned off might not be related to your problem. When I turn my engine off the vacuum amplifier (located on the passenger side of the front bumper) drains its excess pressure and makes a hissing noise for a few minutes. Is your knob for adjusting where your heat/air comes out working properly?

2000 xj,
Eric

Honestly this sounds like a head gasket leak. There are two different main indicators for head gasket leaks: Water in the oil, and exhaust in the coolant. It sounds like you've got the second indicator.
During the combustion event the exhaust is pushed into the water jackets. If I'm correct, the hissing you hear after you turn off the Jeep is the built up exhaust gas and the pressure still left in any cylinders that were on their compression stroke escaping from the cooling system. The pressure from these is going to be much higher that the coolant pressure and the cap pressure. Your temperature gauge may not show that your engine is getting hot in the earlier stages, most don't.
The reason the heat takes forever is because the exhaust gases are taking the place of the coolant in the heating lines. This is also the reason for the coolant leak.
Every 1999 and older Toyota I've worked on and many Cadillacs these were the symptoms for a head gasket leak instead of the water in oil.
The way I always verify this is by taking a compression tester hose, removing the Schroeder valve, and connecting it to my air tool lines. I then rotate the cylinder to be tested until the valves are closed and pump compressed air in. Do that to all of the cylinders and listen for any hissing from the cooling system.

hubs97xj said:

Guessing vacuum or AC leak, but some details here (how long it hisses, is it only when off, does it smell like gas, is it cold, is it hot, does it stop after a few minutes, etc) would help. There are something like 4 vacuum lines, the 2 lines on the purge solenoid, 2 on the can, 1 to the vac can, the AC lines, the blend door line- surely there's something that looks like it should be plugged in?

Click to expand...

Hisses when on and then for about 20 seconds when off and only happens once the engine heats up. I believe my radiator has a small leak.

But, as you can see in the pictures that hose leads to nothing and blows constant air out only while running

I have that same 20sec hiss just after the engine runs, im thinking its a vac leak somewhere.

Is that hose really short and connected to something sticking through the firewall? Looks like it is to me.

Pretty sure that's your HVAC condensation drain line. It's supposed to have some sort of a constrictor or something on it to only let water through I think, but I am not certain. I haven't had much experience working on the HVAC system yet.

I have the same hiss.... so at least you know you're not alone.

The hose in the picture comes out of the firewall and then has a 90 degree turn facing the ground. This hose does not hiss, it only has a constant flow of air coming out of it when the engine is on... My thinking is that potentially this was affecting my vaccum system and is partially to blame for my no/slow heat.

From your latest description DEFINITELY the condensation drain tube from the HVAC box.

Probably not affecting the vacuum system.

Does your engine get up to normal operating temperature quickly? i.e. is it at approximately 210 degrees within ~5-10 minutes of driving? If not, you may need to replace your thermostat, it could be stuck open.

No, the jeep seems to reach normal op temp in the correct time. The AC condensor is infront of the radiator correct? I believe the hissing is coming from there... again I'm so green when it comes to anything HVAC, cooling, etc... thanks for the help guys.