Have heat sometimes. replace radiator,thermasta and water pump. Flushes sysytem. Flushed heatr core 3 different times.works for awile then stops???? 2001 jeep cherokee. my heater core isn't leaking but antifreeze was really rusty...is heater core bad or heater control valve

Check the coolant level in the radiator. If the coolant gets low enough the heater is the first thing to stop working. If there is plenty of coolant and the temp gauge is get in up to the half way mark than it's possible the heater core is just about plugged up. Your local repair shop should be familiar with flushing the heater core. I have had many successful heater core flushes over the years and it can save you thousands. If the heater core is successfully flushed it may not be a bad idea to have the coolant flushed at the same time.

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While it doesn't seem likely, if you've changed, or had the thermostat changed.... I'd say you got a faulty thermostat. I am curious as to what your temperature gauge says the temperature of the engine and coolant is.. If your gauge is showing hot, I can think of two more possibilities... the water pump isn't pumping right... and, if the water pump isn't working right, the problem can be a cracked head or block, which can cause an airlock in the coolant system. Check the coolant or radiator cap.

my 98 Blazer I had to replace radiator water pump heatercore and hoses. Had head gasket go. Once that happens air and dexcool corrode cooling system. Do you smell antifreeze? Are you loosing antifreeze? Check oil see if its another color not clear or black but i think light brown. Have you flushed out system?

If both heater hoses are getting hot, the problem could be a stuck blend door under the dash.
If only one hose is getting hot, there is a blockage in the coolant flow somewhere.

i know you said you flushed the radiator i would flush the engine as well and make sure all is flowing good it also could be a blocked heater core flushing might help. whats happening when you idle up the engine you are forcing the water to flow through the restriction

I have the same truck, I have flushed the radiator both ways, flushed the heater core both ways flushed the engine four times, I have owned this truck for eight years and still cannot get it to heat up the cab. It will keep the windshield defrosted but that is all. If you find any tricks to fix this let me know PLEASE

If you have flushed the heater, I assume you did this by removing the hoses from the thermostat housing. If there's still no heat, check

1. the thermostat is actually present. If not, put one in. If the radiator core is in bad shape, or blocked, replace the radiator.

2. the thermostat is not jammed open. If so, replace it and use a new gasket under the cap.

3. Verify that the water pump belt is not loose.

4. Remove some dash panels to get access to the heater core valve. Check that the valve is actually turning when you adjust the dash control.

Sounds like you have a heat transfer problem. First, on a 91, it's likely that the inside of your radiator is partially obstructed with calcium, rust or both. I know that you flushed it but often the flush will go around the obstruction and will only clean the parts that are already flowing (does little good). Rust does not dissolve easily using over the counter flushes and flushing in the vehicle often leaves debris in the tank which will get right back into the core as soon as you start the engine up again. sometimes it can be commercially cleaned, other times you need to just replace it. Air flow can also be impaired...check that the a/c condenser and the face of the radiator between it and the condenser are clean and not packed with bugs, leaves or other debris.

You may have air in the system. Let the engine run with the radiator cap off until the thermostat opens. Have someone then get in the truck and bring the rpm up to 1800 to 2000 rpm and hold it there for 15 to 20 seconds while you top off the system with coolant and put the radiator cap tightly back on. Then bring the rpm down to idle and road test the truck. DO NOT BRING THE RPM BACK DOWN TO IDLE UNTIL THE RADIATOR CAP HAS BEEN INSTALLED COMPLETELY. I suggest replacing the radiator cap at this time also.

There are products out there like stop leak that MIGHT stop the radiator leak. However... the only real repair is either to have it soldered (if the end caps are not plastic) or replace the radiator all together.

Adding a product like "Stop Leak" most often starts to introduce other problems to your vehicle like a future water pump seal failure or clogs in the smaller water passages in the engine block, heads and manifolds and the thermostat heater bypass hole. Anyone that has ever done any major engine repairs will know immediately if stop leak was used in a cooling system.

The best fix is to replace the radiator.

Many radiators today can not be repaired

Stop leak is in most any auto parts store. Just be advised of what you can expect down the road.

specifically

1. warmer than usual engine operating temps
2. water pump seal failure
3. heatrer core clog (no heat)
4. passenger heat control temp valve clog (no heat)
The choice is yours. Personally I would not do the "Stop Leak" treatment attempt. Sometimes it works other times it does not.