I have a 93 240sx vert. While I eventually get good heat, it takes a good 15 to 20 min AFTER the temp gage shows it is warm. I have changed the thermostat, took hoses off heater core at firewall and blew compressed air through to check for restrictions. After putting the hoses back on to the heater core, I started car and noticed the top hose got very warm, while the bottom hose did not change at all temp wise. This is making me wonder if perhaps since instead of having a cable/valve temp control for the water going to heater core, we have it controlled electronicly, if my climate control switch could be bad not allowing the valve to open fully to the heater core? What do you guys think?

you have air pockets going to the heater core thats why its taking that long for heat to come out you need to bleed the system good . also you have have to make sure the coolant is 50/50 because if ts not and theres not enough water mixture coolant dosent evaporate and make heat its water in the mixture that makes the heat .

niterider93 wrote:you have air pockets going to the heater core thats why its taking that long for heat to come out you need to bleed the system good . also you have have to make sure the coolant is 50/50 because if ts not and theres not enough water mixture coolant dosent evaporate and make heat its water in the mixture that makes the heat .

In theory the air pockets would make sense, except if that were the case, I would also see fluctuations in the engine heat wouldn't I? The system has been opened up 2 times over the past 2 weeks also with the changing of thermostat, blowing out of heater core. Also, if it were air pockets, would not the time needed to get actual heat be different each time rather then the 15 to 20 min after temp gage shows normal operating temp? Its these things that are leading me to believe 1 of 2 things, but I am not familiar with these systems, so I am not sure.

1- The temp control switch on my climate control is not operating correctly and even though I have it in the hot position, (all the way to right) it is not allowing the valve to open all the way to let the hot water into the heater core, thus it taking longer for heater core to heat up then it should.

2- The temp control valve itself is not operating correctly, causing same problem as above.

Anybody think I am thinking on right path? If so, how do I diagnose to be sure? Where is the actual valve that controls water flow to heater core?

i think you have an air pocket also. jakc the front of the car up and use a "coolant funnel" filled half way. run the car till its warmed up and then hold the rpm at 2500 while watching the funnel. if the air pocket "pops" you will sell the level in the funnel go down.

how do you know the climate control swithes are not functioning? most nissan's have always blended the hvac air temp in the heater box not by controlling coolant flow to the heater core.

driftingmy240sx wrote:i think you have an air pocket also. jakc the front of the car up and use a "coolant funnel" filled half way. run the car till its warmed up and then hold the rpm at 2500 while watching the funnel. if the air pocket "pops" you will sell the level in the funnel go down.

how do you know the climate control swithes are not functioning? most nissan's have always blended the hvac air temp in the heater box not by controlling coolant flow to the heater core.

You mean there is no flow valve that controls the water going to the heater core? How does the heat not get into car in summer then? I was thinking today that my top hose going into the heater core got warm pretty fast, while the bottom hose remained cool. I am wondering if maybe the flow valve works off the bottom hose going to heater core. If so, it makes sense that the hoses are reversed and the water going to the flow valve is coming from rad rather then the block??? This would explain why it takes so long to heat up. Could someone with a good working heater check and see if their bottom hose heats up before their top hose?

niterider93 wrote:you have air pockets going to the heater core thats why its taking that long for heat to come out you need to bleed the system good . also you have have to make sure the coolant is 50/50 because if ts not and theres not enough water mixture coolant dosent evaporate and make heat its water in the mixture that makes the heat .

Is there a specific way to bleed the air out of system, or do I just open rad cap with a coolant funnel filled half way and hope air bubble pops?????? I am not understanding here, this is stuff I have not heard of before???

Well, I am going to try the best way I understand. Going to Jack car up as high as I can, take cap off and run car. Hopefully this will get the "air bubbles" out????

Well I did it. I had the front so high, the muffler was touching the ground! It took about 1 1/2 cups of additional antifreeze from the funnel sitting in the top of the rad while running. I won't know for absolute sure until I drive to work tonight, but I believe I am getting heat much faster now. Either way, thanks for your suggestions.