ALLWiTE2JZ

Hey guys I realized that when I turn my heat on in my 1994 SC300 that it will blow cold air sometimes when I first turn it on. Yes, the car is fully warmed up when I try turning it on, but it will blow cold air. When I try turning the HVAC system off in my car and then wait a few moments to turn it back on to try the heat again, it will usually work. Is there any reason for this? The AC has no problems, it works 100% and blows COLD. What could be wrong with my heat though? Anyone have any ideas?

IOWNALEXUS

iTrader: (14)

Check the heater valve on the passenger side firewall, it allows the coolant to circulate into the car giving you heat, you could have a vacuum leak or just a bad valve to check it pop the hood and see if the hose going into the firewall feels warm, if not manually open the valve and it should blow hot.

UpInTheLex

iTrader: (5)

My valve was working and I had the same problem.

I was low on coolant.

Hold the rpm steady at 3K, and see if you get heat.

ALLWiTE2JZ

Okay I will check those things, thanks guys!

O. L. T.

iTrader: (17)

It's the coolant level. Once you turn the heater valve off the flow of the coolant shifts. When you turn it back on it sucks up what is left in the tube then runs dry if it is low. You'd have found this in search, but I'll tell you since you didn't that you need to top the coolant tank off completely.

UpInTheLex

iTrader: (5)

At the time when mine was screwing up, my coolant tank was full. I could fill it to my hearts content, but nothing would make it into the radiator.

So...

I pulled the upper hose off the rad and filled it up that way.

My guess is there was a pressure leak in the system somewhere. I swapped in a 27K mile engine and tank and no more problems. I don't know the exact culprit so I can't say.

I do know my coolant was disappearing and I didn't have any visible leaks. I'm wondering if it was a head gasket or a cracked block, but I didn't have any water in the oil.

vangb2

iTrader: (2)

Do you have a T-Flush installed in your coolant system? If you don't, go buy a flush kit. It's about $5. You may have air trap in your system. With air trap in the system, it may appear that the the coolant level is full but it's not. This kit will allow you to force water through the system to fill up any air. If you don't know how to use one, i'm sure people here can help.

ALLWiTE2JZ

Alright cool, those all sound like likely things that could be wrong with my heat. Thanks again guys.