I changed the cts and maf on my car today as the mpg is not that great .

I drained all coolant from my car and refilled using the my snap vacuum system which normally works fine .

My car gets upto temperature fine and the heaters blow out hot air fine . But I noticed that the bottom rad hose stays stone cold . Thermostat or air lock ? Any help will be really appreciated as always .

Sounds like an air lock, I would be squeezing the rad hoses with the cap removed to try and remove it first off

Fill the rad through the top hose is one thing to try.

Could be a blocked rad though,take top and bottom hoses off and put a hose in the top and see how it flows out

Fill the rad through the top hose is one thing to try.

Could be a blocked rad though,take top and bottom hoses off and put a hose in the top and see how it flows out

Yeah I'll give that a go , good thinking .

Keep some topping-up coolant in the car, then just drive it normally for a few days.If the thermostat really is stuck shut, you'll see it getting too hot, if it isn't, any air in the system will work its way up to the expansion tank.

Today I fitted a new thermostat and flushed the rad through then vacuum filled the system once again . Run it up to temperature and the bottom hose was stone cold again . Didn't run it up so that the fans kicked in though run out of time at work . Is it still an air lock or do these engines take a long time to run up ?

Sounds like an airlock. Did you have the heater in the full heat position while filling? Mine took a while to bleed out by massaging the pipes

Sounds like an efficient diesel engine in winter to me.  Drive it hard for a while, then feel the bottom hose.

 

Heater control position makes no difference to coolant flow through the matrix on these.

Sounds like an efficient diesel engine in winter to me. Drive it hard for a while, then feel the bottom hose.

Heater control position makes no difference to coolant flow through the matrix on these.

I did not know that, thanks for the info

Sounds like an efficient diesel engine in winter to me.  Drive it hard for a while, then feel the bottom hose.

 

Heater control position makes no difference to coolant flow through the matrix on these.

Thats what I thought . I'll just keep an eye on it .

I did not know that, thanks for the info

That only applied back in the days of old minis etc when the heat control actually isolated the coolant from the matrix, its just a flap now in modern heaters that diverts either hot air from the matrix or cold air from the outside.

That only applied back in the days of old minis etc when the heat control actually isolated the coolant from the matrix, its just a flap now in modern heaters that diverts either hot air from the matrix or cold air from the outside.

I'm sure my mk5 (2001) fiesta had an actual valve in the coolant pipes going to the matrix, because they were prone to breaking up leaving you with no heat, that's why I thought the fabia might have one.