Heater intermittent

[fordup]

On my 2013 limited the heater will blow hot air for about 1/2 hour then nothing but cold air from then on. Coolant level is full. This has been going on for several years. Dealer keeps saying it works fine- no problems found. Help please

 

[flyrv9]

Some vehicles (I'm not sure if the 4Runner has one, but I would guess it does) have a heater switch/valve which is in the input heater hose (under the hood). When you adjust the temp control, it opens and closes to regulate the flow of hot water into the heater core. It's pretty common on older vehicles for these valves to freeze closed. This prevents hot water from entering the heater core and you get no - or little heat. I would check there first, and also look to see if the control cable is ok. You should be able to follow the heater hoses and find it.

 

[fkheath]

Some vehicles (I'm not sure if the 4Runner has one, but I would guess it does) have a heater switch/valve which is in the input heater hose (under the hood). When you adjust the temp control, it opens and closes to regulate the flow of hot water into the heater core. It's pretty common on older vehicles for these valves to freeze closed. This prevents hot water from entering the heater core and you get no - or little heat. I would check there first, and also look to see if the control cable is ok. You should be able to follow the heater hoses and find it.

Also, have you had the coolant changed recently? An air bubble can cause heater problems. There is a procedure to purge any air out of the coolant system when it is changed.

 

[speedmaster]

Hmmm. Is the truck's temp correct and stable? If it was me I get a full flush of the coolant system and see if that solved it.