Polo 6n 1400 boiling over

[Ma Wills]

Hi can anyone advise?
1999 polo, boiling over, so have changed thermostat, temp sender and fan switch.
Fan not coming on automatically, but will when jumped.
Top hose gets hot, bottom hose and bottom of radiator stays cold. Apparent air lock.
Have flushed radiator and squeezed hoses with expansion cap off untill car is hot.

Can anyone help with ideas to stop overheating, remove air lock and advise why fan is not coming on.

Thank you
marky

[Rob69]

When you say boiling over, is it actually boiling with temp gauge in the red, or is it gassing up, indicating head gasket gone? Is the coolant circulating or could the water pump impellor have come adrift. A sniff test would show exhaust gas in the header. Fan might not be coming on because it's not required in colder ambient temperatures unless the engine has been worked hard then the car stops and there is no air flow through the rad. My polo 9n rarely came on unless in traffic.

[grant19841]

Head gasket kit on ebay around 40 quid, just to rule out suspicion.

Sent from my SM-A300FU using Tapatalk

[niall campbell]

With age of car, it will be blocked radiator .

To get rid of air lock, switch engine on, put heater to maximum on heat, put fan for heater to max as well & run for 10 minutes.

Could also be water pump has failed, get one with metal propellors rather than plastic.

Go for timing belt and water pump at same time,

You can actually take radiator off and get it tested for its flow through rate.

Make sure you are putting pink antifreeze in, you cannot mix pink with blue or chokes up .......................... usually in heater matrix.

[Ma Wills]

Hi, Temp gauge sits in middle on tickover will rise when driven, coolant appears to be circulating in expansion tank. Re head gasket, I have filled with water run upto temp and drained several times, water looks clean when coming out. Although head gasket is beyond my capabillities I will get it checked as last resort.

[Ma Wills]

Hi, Agree could be blocked radiator. Pump appears to be working as can see water circulating in expansion tank.
I am thinking new thermostat could be stuck ( when I looked at it the needle was poking through centre hole of housing cap) maybe this is preventing water circulating, as bottom hose and bottom of radiator stays cold.
Is it wise to remove stat and run engine to see if rad and hose gets warm?

[niall campbell]

If you remove stat, it wont do any harm; just water will be luke warm at best.

If you still have the old stat, you could put in a pot of cold water with new stat, heat the water and see if they open at same time ................... and open fully

Also the fins in the radiator can be choked with flies and dust and more debris, or the fins have bent over restricting the flow of air through it.

Your cheapest option is to check the stat with old one, then replace the radiator

The only thing I can think of is, that have you replaced the water temp sender unit for the fan ? Or was it the one for the dashboard ? That's if the Polo has 2 water temp sender units ............ I would say it has, as most cars do ............................ its easy to do a schoolboy error.

Also another thing is the expansion cap, this is pressurised and aids circulation. Are you screwing on until it clicks ? That may need replacing and is cheap to do so ............... often overlooked

[Rob69]

In your OP you said you'd flushed the rad, presuming you got a good flow when flushing, and you can see water circulating in the header indicating impellor is turning at tickover anyway, top hose is hot, bottom hose is cold, indicating the rad is cooling the water as it flows through. I've not found these to be prone to air locks and self bleed ok. Normal temp at tickover and high temp when driven, could be a sticky stat but my money's on the head gasket,

[niall campbell]

the radiator may be cooling the water, just the flow may be too slow . The only way to check radiator is a flow test.

Head gasket would show water in oil or vice versa, white smoke in exhaust, warped radiator or burst pipes . Water loss.

[Ma Wills]

Ok, I removed stat and run engine to mid temperature. Both top and bottom hoses got hot as well as all of rad, the fan also kicked into life.
The needle of the thermostat was poking through centre of housing (coolant flange), don't think that should happen,so today I purchased new flange(with cross member/bridge in centre for needle rather than hole as I believe this assists stat to open and close.
Will fit, refill and test over weekend.
I am thinking/hoping the broken housing was issue rather than new fan switch. temp sender and stat.
Also crossing fingers head gasket is ok.
Will update with outcome
Thank you all for help with this.