Heater question

[porkchop-rob]

Working on my 2000 Wrangler 4.0.

Started with ZERO heat.
1. Pulled the heater hoses and flushed back and forth with the water hose until i got good flow both directions.
2. Filled the core up with CLR and let it sit for 20 minutes, then flushed both ways with the water hose (did this 2 times)
3. Poured a bottle of flush into the system and drove around for a few days.

We've gone from no heat to "meh" heat - (Heater is HOT for the first few seconds then warmish at best).
4. Flushed the system a couple times with fresh water and filled up with coolant before the freezing weather last week.
5. I have replaced the radiator cap (wasn't building pressure)
6. Replaced upper radiator hose (started leaking once the system would pressure up some)

Thermostat was replaced last year by a local mechanic. Jeep stays at ~200-205° all the time. No overheating. No smoke. No engine driveability issues. Just an old jeep.

I **think** the issue now is low/slow flow of hot water through the heater core. It is flowing (both hoses are warm) but I'm not convinced it is flowing quickly enough. Either there is not enough pressure...or there is still a restriction.

Questions: How much pressure should there be in the water headed to the heater core? I can literally hold my thumb over the hose and stop ALL flow. Is this normal? Could I have a corroded/weak water pump? Does the system require pressure to build before it "forces" water through the heater core? How much "restriction" should I feel when blowing air or pumping water through the heater core?

Any help appreciated!

 

[Chris]

Working on my 2000 Wrangler 4.0.

Started with ZERO heat.
1. Pulled the heater hoses and flushed back and forth with the water hose until i got good flow both directions.
2. Filled the core up with CLR and let it sit for 20 minutes, then flushed both ways with the water hose (did this 2 times)
3. Poured a bottle of flush into the system and drove around for a few days.

We've gone from no heat to "meh" heat - (Heater is HOT for the first few seconds then warmish at best).
4. Flushed the system a couple times with fresh water and filled up with coolant before the freezing weather last week.
5. I have replaced the radiator cap (wasn't building pressure)
6. Replaced upper radiator hose (started leaking once the system would pressure up some)

Thermostat was replaced last year by a local mechanic. Jeep stays at ~200-205° all the time. No overheating. No smoke. No engine driveability issues. Just an old jeep.

I **think** the issue now is low/slow flow of hot water through the heater core. It is flowing (both hoses are warm) but I'm not convinced it is flowing quickly enough. Either there is not enough pressure...or there is still a restriction.

Questions: How much pressure should there be in the water headed to the heater core? I can literally hold my thumb over the hose and stop ALL flow. Is this normal? Could I have a corroded/weak water pump? Does the system require pressure to build before it "forces" water through the heater core? How much "restriction" should I feel when blowing air or pumping water through the heater core?

Any help appreciated!

Here's some things worth looking at:

Heater Core Flow: You're correct that the heater core relies on good flow through it to produce heat. Holding your thumb over the hose and stopping flow isn't typical and suggests there could be significant restriction or a weak pump. In a functioning system, you should feel a decent amount of pressure when the engine is running.

2. Water Pump Performance: A failing or corroded water pump could definitely lead to reduced flow. If the pump isn’t circulating coolant effectively, that could explain the “meh” heat. If you can access it, inspecting for leaks or abnormal noises might give you more clues about its condition.

3. Checking Pressure: Generally, the cooling system should build pressure to around 15-16 PSI with a good radiator cap in place. If the cap isn’t functioning well, it won’t help pressurize the system properly, even after your replacement. Confirm that the new cap is the correct rating for your Jeep.

4. Air in the System: Make sure you've bled the cooling system thoroughly. Trapped air can create hot spots and limit flow to the heater core, making it feel like the flow is restricted.

5. Restrictive Hoses: Sometimes, the hoses themselves can collapse internally or block flow if they’re old and degraded. Inspect the hoses for bulges or weak spots when the engine is running and fully warmed up.

6. Heater Control Valve: If your Jeep has a heater control valve, make sure it’s functioning properly. Sometimes they can get stuck or partially closed, limiting the flow to the heater core.

7. Quick Check: With the engine running and the heater on high, check the temperature of both heater hoses at the core. They should be nearly the same temperature if flow is adequate. A significant difference can indicate that there’s a problem with the core, a blockage, or an issue with the valve.

If you’ve gone through all of this and the issue persists, a further inspection of the heater core itself might be necessary. Sometimes, despite flushing, residues can still cause partial clogs, particularly if the core is old.

Hope some of this helps! Good luck, and let us know what you find out.

 

[Rancho LJ]

It could also be the blend door inside of the HVAC box or the actuator for that door. Look up Heater Treater for 97-06 Wrangler. There's a pretty good explanation on this page.

https://heatertreater.net/jeep-wrangler-97-06

 

[porkchop-rob]

Here's some things worth looking at:

Heater Core Flow: You're correct that the heater core relies on good flow through it to produce heat. Holding your thumb over the hose and stopping flow isn't typical and suggests there could be significant restriction or a weak pump. In a functioning system, you should feel a decent amount of pressure when the engine is running.

2. Water Pump Performance: A failing or corroded water pump could definitely lead to reduced flow. If the pump isn’t circulating coolant effectively, that could explain the “meh” heat. If you can access it, inspecting for leaks or abnormal noises might give you more clues about its condition.

3. Checking Pressure: Generally, the cooling system should build pressure to around 15-16 PSI with a good radiator cap in place. If the cap isn’t functioning well, it won’t help pressurize the system properly, even after your replacement. Confirm that the new cap is the correct rating for your Jeep.

I will check the pressure this evening. Hopefully it holds!

 

[KennethS]

2. Water Pump Performance: A failing or corroded water pump could definitely lead to reduced flow. If the pump isn’t circulating coolant effectively, that could explain the “meh” heat.

If reduced water pump output was happening, it seems like the engine would be running hotter than normal due to the "low flow" from the water pump.

 

[bohuggabee]

Working on my 2000 Wrangler 4.0.

Started with ZERO heat.
1. Pulled the heater hoses and flushed back and forth with the water hose until i got good flow both directions.
2. Filled the core up with CLR and let it sit for 20 minutes, then flushed both ways with the water hose (did this 2 times)
3. Poured a bottle of flush into the system and drove around for a few days.

We've gone from no heat to "meh" heat - (Heater is HOT for the first few seconds then warmish at best).
4. Flushed the system a couple times with fresh water and filled up with coolant before the freezing weather last week.
5. I have replaced the radiator cap (wasn't building pressure)
6. Replaced upper radiator hose (started leaking once the system would pressure up some)

Thermostat was replaced last year by a local mechanic. Jeep stays at ~200-205° all the time. No overheating. No smoke. No engine driveability issues. Just an old jeep.

I **think** the issue now is low/slow flow of hot water through the heater core. It is flowing (both hoses are warm) but I'm not convinced it is flowing quickly enough. Either there is not enough pressure...or there is still a restriction.

Questions: How much pressure should there be in the water headed to the heater core? I can literally hold my thumb over the hose and stop ALL flow. Is this normal? Could I have a corroded/weak water pump? Does the system require pressure to build before it "forces" water through the heater core? How much "restriction" should I feel when blowing air or pumping water through the heater core?

Any help appreciated!

Sounds like you either have a clogged heater core or you yourself might have a health condition? Do you still feel heat near an oven or in sunlight?