Cabin Heater Only heats in High RPMs

Have your thermostat checked, sound like it is not working when cold.

Hi Paul, check the engine coolant level, the thermostat and the valve operation which controls the coolant going into the cabin heater. The most likely problem would be with the heater regulator valve.You'll find that located on the fire wall between the engine and cabin. It will have two hoses and an adjustment device fitted. It very well may be stuck. Regards John

time to change water pump by passing or vortexting so to speak

replace the heating core but change the antifreeze first and clean the system and make sure there's no stop leak in the hoses. you will need to flush the heater core out completely several times to know for sure.

You need to bleed the cooling system of excess air and add aditional antifreeze.

Your likely problem is low coolant level. Check to make certain that your coolant level is topped up in the radiator and that coolant is also in the reservoir at the appropraite level as shown when on container when the engine is hot or cold. When the coolant is low, you have to have higher RPMs to get the coolant to pump through the system and heater core.

2008, take it in for warranty work.

The reason its not working is that it uses vacuum to open the heater vent. At low idle there is not enough vacuum to open the vent, soyou get just cold air. Sounds like therer is a leak in the hose which is covered under your warranty.

Just finished fixing my daughters 1999 taurus heat. It would blow warm only when running down the road. At idle it blew cold. I started with replacing thermostat, and water pump because they are the easier fix. Still did not help. Then I replaced the heater core. A daunting job but not that hard to move the dash slighly out of the way to replace. There is a good write up at tarusclub.com. After that, heat was better but at idle, it would still blow cool sometimes. Researched and found answer. Park car on the steepest hill you can find with front of car up. Start car and take off reservoir cap. Let car warm up and keep rpms about 1500. After a while the fluid will come running out of the car and all over the place but it will bring air bubbles with it. Reduce rpm, add more fluid and repeat about 3 times. It will make a mess but after that, the heater works perfectly. We get heat long before the temp gage indicates any and it never blows cold unless you lower the temp.

You most likely have an air pocket in the cooling system. The heater core on these vans is much higher than the engine and they can be tough to get all the air out of them.

Make sure the coolant in the radiator is full when engine is cold- also fill the overflow bottle to the top. Chock the rear wheels. Jack up the front of the van as far as you can and support with jack stands. Run the engine until it's warm and then hold the RPMS at 2000 for about 5 minutes while checking for heat inside the cabin. You may hear some funny noises like something is trying to come through the firewall forcefully! That's the air pocket moving... you might not hear this also. Once you have good heat inside, let the engine idle- if the air coming form the vents cools off after a couple minutes, the air is still there- keep doing this until the air is hot coming from the vents at idle for more than a couple minutes. Once you have good heat, turn the engine off and let the engine cool completely- at least a couple hours... you will most likely see the level in the overflow drop dramatically. Lower vehicle and make sure overflow is at COLD FULL mark.

Newer Altimas also had a similar situation in which heat would go away at idle- usually not a problem with an air pocket, but Nissan has a bulletin out on putting the correct concentration of coolant/water in the system- these cars are very sensitive to changes in coolant mixture concentration.

Nissan Scope Technician- 10 years with Nissan