Mk1 Heaters not working properly...

[KevSeymour]

...since i did a coolant change.

I've bled and re-bled the system by running the engine and pulsing the pipes, topping up the level as i go. I get to the point where no more bubbles are coming out so i finish. Put the cap back on and fill the expansion tank to the maximum level. For a couple of days after this the coolant system appears to pressurise properly, but soon appears to not pressurise at all.

If i start the car and drive off without letting it idle for 5-10 minutes, i'll get no heat through my vents for my entire journey - regardless of how long that journey is. Previously it would be warming up within a couple of minutes.

If i let the car idle for 5-10 minutes before setting off it's lovely and warm to get into, but soon cools down when on the move. Similarly if at any point in a journey i sit still idling, after a while i get some heat.

This makes me think i'm only getting any heat due to heat-soak somewhere in the system rather than a properly functioning heater.

Also, i appear to be losing coolant, i have no drips and i don't suspect the head gasket (no mayo in the oil cap), because every time i check (which admittedly isn't all that often, maybe every couple of weeks) the expansion tank is empty.

What am i doing wrong?

[Eighteeteewhy]

What is the temp gauge doing? It should sit halfway pretty much all the time.

Ah didn't read properly, sound like your thermostat could be stuck open?

[KevSeymour]

Temp gauge is as you say, doesn't ever get hotter than halfway. Will look into the stat, cheers.

[Eighteeteewhy]

KevSeymour said:

Temp gauge is as you say, doesn't ever get hotter than halfway. Will look into the stat, cheers.

Does the gauge drop when you drive?

[KevSeymour]

I think it does if left to idle, it'll dip then rise up again.

[trace1967]

KevSeymour said:

...since i did a coolant change.

I've bled and re-bled the system by running the engine and pulsing the pipes, topping up the level as i go. I get to the point where no more bubbles are coming out so i finish. Put the cap back on and fill the expansion tank to the maximum level. For a couple of days after this the coolant system appears to pressurise properly, but soon appears to not pressurise at all.

If i start the car and drive off without letting it idle for 5-10 minutes, i'll get no heat through my vents for my entire journey - regardless of how long that journey is. Previously it would be warming up within a couple of minutes.

If i let the car idle for 5-10 minutes before setting off it's lovely and warm to get into, but soon cools down when on the move. Similarly if at any point in a journey i sit still idling, after a while i get some heat.

This makes me think i'm only getting any heat due to heat-soak somewhere in the system rather than a properly functioning heater.

Also, i appear to be losing coolant, i have no drips and i don't suspect the head gasket (no mayo in the oil cap), because every time i check (which admittedly isn't all that often, maybe every couple of weeks) the expansion tank is empty.

What am i doing wrong?

Its the thermostat thats what was happening with mine. Mine was stuck open when removed. Order from autolink using discount code 'solent' for mx5oc discount.

[KevSeymour]

Excellent, thanks!

[Eighteeteewhy]

How's this going Kev? Nice toasty heaters yet?

[KevSeymour]

I re-bled the system the other day, someone suggested that i should be doing it with the heaters on full blast with the recirc on - i didn't think it mattered but was worth a try.

No joy.

I've got a new stat waiting to go in tomorrow.

Thanks for checking though!

[KevSeymour]

Just replaced the stat, was stuck open just as you said. New one in and hot air billowing from the vents, Woohoo!

Cheers.

[Eighteeteewhy]

KevSeymour said:

Just replaced the stat, was stuck open just as you said. New one in and hot air billowing from the vents, Woohoo!

Cheers.

Tidy