Hi all,
Have recently done some work to my 07' Fit on the cooling system. The car has the L15a 1.5 litre engine. Basically I replaced the thermostat as the thermostat in the vehicle was old. I replaced the coolant and the car developed an airlock in the cooling system, (rushing water sound behind dash).

I have bled/burped the system today by idling the car with the radiator cap off on an elevated surface, I squeezed all the hoses including the heater hoses to expel air from the system until air bubbles stopped appearing in the radiator filler cap, then replaced the cap with a decent amount of coolant in the radiator and topped off the overflow reservoir.

Now however there is no heat from the heater, the car does not appear to overheat after a 15 minute drive no red light illuminates etc and engine does not seem overly hot, the bottom radiator hose was warm the top one hot, the lower firewall heater hose is hot but the top one is cold which I guess indicates a problem in the heater core with coolant circulation. Does anyone have any thoughts, is it possible there is still a massive air pocket in the heater core even though no air bubbles are apparent? The replacement thermostat was genuine Honda OEM 82 degree and I am positive it was installed properly and in the correct orientation.

Would really appreciate if anyone has any thoughts on this.

Thanks

 

Yep, surely there is a remaining air pocket in the heater matrix.

Idling the engine won't clear the air, you need a faster coolant flow to do that. What I do is to run the engine at relatively high RPM (while driving) then top off the coolant before the next drive. That gets the air out.

Note that you will probably need to monitor coolant levels for the next few weeks. It WILL drop.


Final note: With Honda's reverse-flow cooling system (bottom to top), often you need to warm the engine THEN SHUT IT OFF to get the T-stat to open, initially. I'm sure you have achieved that by now but I wanted to mention it.

 

Ok thanks will try that. By a relatively high rpm do you mean 3000-3500 kind of range? Would anything be achieved by bleeding it again at a higher rpm? I will see if the heat improves over the next few days. Thanks.

 

Also am I best to add the coolant via the overflow reservoir only? I'm assuming adding more coolant to the radiator and lifting the cap will introduce more air into the system, correct? Thanks.

 

On a cold engine, open the cap, the coolant fill should be very close to the neck of the filler. If the rad level is low but the plastic reservoir is constant, you need to buy a new pressure cap. But normally, you only need to check the reservoir.

Regards bleeding, at the first fill, I assure that the level is proper, then drive around my one-mile-block in first gear, yes 2500 - 3000 RPM. Then top up.

On subsequent drives I rev past that on a warmed up engine (remember we have manual trannies). I 'run thru the gears' up near redline.

PS, I may have assumed this, but of course you need the heater on HIGH during these exercises...


(Not sure about the Fit but many new cars will not let you rev the engine too high out of gear, at rest.)

 

Thanks for the advice really appreciate it. Drove the car tonight series of short bursts through the gears near redline and around the block at 3000 rpm in first and I am getting some cabin heat now.