Front heater blowing cold !!!

The van had GOOD heat all through December... I had the oil changed (genuine Toyota filter and synthetic oil) just before Christmas...I haven't used it since then, but, on the ride home from the oil change- and now with further testing - I have warm air at the rear heater vents and ""COOL" air in the front ...WHAT CHANGED ??? is the synthetic oil the problem? (i know, that's probably a dumb question-but, I always used natural oil till now). Under the van I have a warm hose and a cool hose leading to the front heater core. Could my front heater core suddenly be blocked??? It must be nearly impossible to replace that heater core, right??? Would you suggest trying a coolant flush ??? By the way, a year ago I bypassed the little valve that controls the hot water flow to the heater core (the valve under the front of the van that has the blue control cable from the dashboard connected to it) ... however, I have had good heat since then for a year, so, that probably can't be the issue. Shoot me your best suggestions, PLEASE.

I'd review this first. Then I'd probably do a full coolant flush with special attention to the front heater core, also checking heater hoses along the way and replacing the ones that seem compromised.

If your temp gauge and rear heater are normal then it's not the oil. You did have strangers digging around in your van, though, so it's possible they did something while in there.

First I'd check the coolant levels. With the engine cold, remove the radiator cap and make sure it's full to the top.

I'm going off memory here, haven't dug into my heater components for a couple of years. As I recall the heater lever controls that valve you removed and also a flap that controls whether the air passes over the heater core. Maybe you don't look at the temp lever anymore because you don't use it. Make sure it is in the heating position. If that's not it, get underneath and look at your old bypass job to make sure nothing was monkeyed with under there. Make sure none of the heater hoses are pinched.

Also.. how cold did it get where you are this year? Is it possible the coolant froze and bent or burst something in the heater core?

Okay, yesterday I gave the van a good ride and I got actual heat from the front heater. It heats fine once I start putting a load on the engine. I reported good heat in December, and, all those days were about 45 degrees outside. During my warm-up and idle test yesterday it was about 12 degrees here. The old van needs to do a little work when it's that cold out if I want good heat. I will definitely check the position of the flapper door that exposes the fan air to the heater core. Not only do I need it open all the way now, I also need it closed in summer...(I have no A.C.). --thanks a lot for all the insight.

I agree with the above posts. 1st thing to do is verify van is at normal operating temps (heater can't blow hot if coolant isn't hot). If engine is running @ normal temp, but the heater isn't blowing hot, then it's an obstruction in the heater system. Since the valve has been removed, that only leaves the core. If your system has contamination these plug up pretty easy. A few months ago I resurrected a van that had been sitting for several years. the cooling system was extremely contaminated (coolant was all rusty looking). The van ran and would warm up, but the heater blew cold. After a thorough flushing of the cooling system the heater started working again.

If a standard flush doesn't do the job, a back-flush & flow test of the core might be in order. This can be done by disconnecting both hoses going to the core (under the van) then using a garden hose, force water through both directions. An unobstructed core should be able to keep up with normal hose volume. Good luck. Tim

Quote:

---

Originally Posted by timsrv

I agree with the above posts. 1st thing to do is verify van is at normal operating temps (heater can't blow hot if coolant isn't hot). If engine is running @ normal temp, but the heater isn't blowing hot, then it's an obstruction in the heater system. Since the valve has been removed, that only leaves the core. If your system has contamination these plug up pretty easy. A few months ago I resurrected a van that had been sitting for several years. the cooling system was extremely contaminated (coolant was all rusty looking). The van ran and would warm up, but the heater blew cold. After a thorough flushing of the cooling system the heater started working again.

If a standard flush doesn't do the job, a back-flush & flow test of the core might be in order. This can be done by disconnecting both hoses going to the core (under the van) then using a garden hose, force water through both directions. An unobstructed core should be able to keep up with normal hose volume. Good luck. Tim

---

Thanks a million, timsrv ... The van was warmed up (temp gauge at normal) but, if you lived up here you'd know, sometimes that is not enough if you are just sitting at idle in January. I will totally flush the core in summer ... can't do it now. By the way, the inlet hose into the heater core already had the "T" with the garden hose flusher on it when I got the van 13 years ago...I just never used it. thanks again.