I have a 89 si with a b20b swap, I replaced the thermostat last year with a oem honda one. car has a pwr radiator with a new skunk2 radiator cap. Heres the deal. The car was blowing hot heat fine untill we just recently got really cold weather , Now when I drive it it will blow cold, then start blowing hot out of no where, It will blow hot for a little, then back to cold. today I bled the coolant system and it seemed to help but it's still acting crazy. Could that oem thermostat of went bad already? I will gladly pay pal 10 bucks to whoever figures this out

 

Check fluid levels
Flush heater core

Do you smell coolant at all? Any crystallization near your feet? How old is your water pump? Check to see if it's coming out of the weep hole.

 

No coolant smell, coolant level stays full, motor has 45k miles on it, I never changed the water pump. Car does not over heat and the temp guage stays where its supposed to.

 

Need to do a block test on it, see if you've got a blown HG thats allowing exhaust into the coolant system, and therefore air into your heater core. That or else youve got an ultra stubborn air pocket.

 

Sounds like your heater core is working since you do get a bust of hot every now and then.
I think it would be odd to get any heat at all if you had a complete clog.
A partial clog would just be less efficient, but not erratic.

My guess is that your radiator is maybe a little too efficient.
Since it's cold outside, maybe the water in the radiator is getting too cold.
The engine water heats up to open the thermostat and allows the cold water from the radiator through the thermostat.
Being such cold water, maybe it closes the thermostat really fast.

Try blocking off half the radiator with some cardboard?

 

I think you should get a look at the proportioning valves on the heater line, near the firewall, where the coolant hose enter into the cab to the heater core.

make shure the buterfly work's according to the control of the thermostat in the dash,
the butterfly may be loose or the plastic arm broken and it disturb the flow of hot water to the core, making erratic hot/cold blowing.

just a thought...

Kranked

 

Do this and let us know if it works

 

I will give this a shot and let you know, last week when it was about 50 Deg. outside my car would start blowing warm arm before the temp guage even went up. Now it goes the whole way to normal and still blows cold. Ill give it a shot though

 

Ill check it out also, not exactly sure what your talking about though?

 

I think the problem is located either in heater hose valve (fwd of the firewall) or the air diversion door under the dash.
When you turn the temp control dial on the climate control it pulls (or pushes) on 2 cables. 1. the heater hose valve and 2. air diversion door.
PM me your number, I'll talk ya through it.

 

^he is probably right...i had a very similar situation mine was the "air diversion door" in combo with a leaf and bug filled evaporator core

 

Explain^

 

Just a little update, today was about 50deg. Outside and the heat was blowing fine, im thinking 4dref was right , im going to try to cardboard thing tommorow, its supposed to be pretty cold. If it works , 10 bucks for 4dref

 

evap core was limiting air flow to the heater core and the diversion dorr was half bypassing the heater core like the a/c was on

 

But that would be like that ll the time.
The flapper wouldn't be opening and closing randomly, would it?

 

buy a sunggie call it a day. wheres my $10

 

no the door was stuck in the middle but with the restricted airflow it made the air swirl funny in the heater box causing it to intermittently go hot or cold