Cooling fans stay on

lugee, May 8, 5:05pm
Long story short: replaced thermostat housing because of corrosion. Replaced thermostat at the same time for good measure. Car runs fine now, no overheats/underheats under any circumstances, but now the cooling fans stay on after coming on at the right temp. Even driving at 80km/h the fans still appear to run, and they won't turn off. The thermostat I replaced it with was the correct temp (77c), but this to me seems its opening too late (the fans come on at 88-90c).
n3d4sp3d, May 8, 5:17pm
vehicle make model year !
jason18, May 8, 5:22pm
If its not overheating or running to cool does it matter!
lugee, May 8, 5:25pm
Yes, because it never used to happen, and it will be using significantly more fuel, not to mention added wear on the fans.
n3d4sp3d, May 8, 5:27pm
yup if it efi it will run rich and use more fuel than it should it may also hunt as ecu makes an attepmt to lean mixture up to compensate for the extra petrol. have you tested the coolant temp sensor it may be reading to high
lugee, May 8, 5:31pm
The fans are controlled by a mechanical temperature switch. not by the ECU. At the monent I'll assume that the switch is OK because the issue started straight after the work on the system.
jason18, May 8, 5:40pm
Did you knock a wire off!
lugee, May 8, 6:01pm
Not as far as I know. The cooling fans operate normally, if I let the car idle for a while with the heat on max the fans will switch off after a minute or so, but won't without the heaters assistance. I just got back from a short drive and the fans were on, but under the bonnet the radiator and bottom hose was cold which tells me the thermostat isn't opening correctly.
doriandarby, May 8, 6:06pm
Maybe an airlock in the system is causing a hotspot to build up around the thermoswitch!

Purely conjecture, not sure if that happens at all.
tmenz, May 8, 6:07pm
The fans will both come on regardless of the temperature when the air conditioning is switched on. Try turning the A/C off.
lugee, May 8, 6:10pm
It is (in fact its permanently off as the safety switch is tripped due to lack of gas. Too expensive to refill as it would need to be converted to the new refridgerant).

Either way, the fans only turn on ONLY once the engine reaches operational temp, but then doesn't turn off.
steve98h, May 11, 6:08pm
cooling fans wil come on around 10c above the thermostat temp.
id put my money on the thermo fan switch.
ceebee2, May 11, 6:42pm
Ensure the coolant has been bled correctly.warm up from cold with radiator cap off and observe the coolant which should NOT bubble at all aftera while. Ensure the heater is ON to bleed air out also, When at near normal temp and no bubbling replace radiator cap, wait for fan to come on and hope fully go off after a short period. NB = Especially if thermostat is fitted in bottom hose area.
audi_s_ate, May 13, 7:14am
Could still be a faulty theromstat - I have had to replace 4 thermostats on honda's I have owned (original lasts about 160k). I have only used genuine Honda ones and I think they are cheaper than buying from supercheap once you have to factor getting the correct gasket etc. I squeeze all the hoses to get as many bubbles out of the system first - cap off and then do it again whilst running, take it for a bit of a thrash to get any remaining air out.