Evening all!

Picked up my Imperial Blue Focus ST170 this morning, and after driving a big Saab 9-3 for a year, I love it! Handles brilliantly, looks good and the engine feels more powerful than the stats and reviews make out...more usable power lower down the rev range compared to my old Clio 182 (although that was a lot faster overall), so I'm happy.

However, something I've noticed;

- Engine temp gauge takes a while to get up to the middle, and tends to drop off a little occasionally, and drop off a lot when the heaters are on full to de-mist. Seem to get warm air out the heaters fairly quick so wasn't sure if it was just a sensitive gauge or maybe something was up?

 

Sounds like a duff thermostat, 5 minute job to change!

 

Thanks for the quick reply! Appreciate it.

Yep, confirmed what I was thinking really...is the thermostat an expensive part do you know? Also I assume I'm not doing any damage to continue driving normally?

 

When i bought one for my old st170 it was about 15 quid i think. That was a few years ago though. The engine isn't running at operating temperature so technically more engine wear is occouring and it will use a bit more fuel so i would want it sorted soon ish!

 

Same issue with my ST. I bought a thermostat for about Ł5 from ebay, an OEM part too! East to fit, three hex head screws hold it in. Make sure you buy one to include a new rubber seal for the thermostat. Give the housing a good clean out too if there is any gunk in the housing. You will have to top up the water level too. You should find the temp needle sits in the middle of the gauge and stays there irregardless of heater, engine load etc, etc. You may also notice engine runs better and fuel economy improves as the engine management system takes engine temp and water temp into account. Mine feels much better now it is warming up properly.

 

Thanks for all the info guys, appreciate it!

I've also noticed it appears to be leaking a bit of coolant from the silver plug on the thermostat housing; is this likely to be related? Also, how come hot air comes out the vents within 5 minutes if the thermostat has failed? Is it likely to be a sensor, and if so, where is the sensor located?

Cheers!

 

Leak won't be related to the thermostat really - lots of them leak here. Remove the plug and clean it up and pop it back in - don't over-tighten it as the thread will strip easily. A copper washer or rubber O ring can help improve the seal.

Flow of hot water the heater matrix is not controlled by the thermostat or the heater controls - as soon as the engine starts warming up it transfers heat to the water in the cylinder block which is continuously pumped through the heater matrix. It is designed like this to get hot air quickly to demist the screen. The temp control knob just operates a flap controlling the amount of hot air from the heater matrix that can enter the car.

All the thermostat does is control the flow of water to the radiator - until the water reaches 98 deg C it stays shut. This maintains the engine at optimum operating temp. The sensors you refer to are for the water temp gauge on the dash and sending a signal to the ECU to control mixture settings. There is a temp sensor in the cylinder head too sending data to the ECU. Clever stuff - until it goes wrong!

You should find the Duratec warms up quickly, even on light throttle openings - 2 miles of normal driving should get the needle to the centre of the range on the temp gauge.

 

Thanks for all the info and detailed reply, very much appreciated.

Ahh I see, so (if I understand correctly) if I've got a duff thermostat then I won't necessarily notice through the heaters.

Is my temp gauges behaviour enough of an indication that it's the thermostat, or is a sensor also a likely culprit?! I'm guessing it is probably the thermostat at this point, as the needle does rise to halfway eventually if I'm sat in traffic, but drops off again when the road clears and doesn't move erratically.

 

Its the thermostat for sure. Hot day (if we ever get one) - stop at traffic lights - needle starts moving up the gauge - start moving again - needle falls. Classic symptoms. Very unlikely to be the sensor - they rarely fail - if you are concerned put a multi-meter across the sensor and see if the resistance changes!

 

Brilliant, thanks. Not too concerned about it being the sensor, just thought I'd exhaust all possibilities.

Out of interest, where should the needle on the oil temp gauge usually sit? Mine barely gets above cold most of the time, but I assumed the oil wouldn't get too hot with average day to day driving. Someone told me that the oil temp gauge is a 'guesstimation' based off the water temp?

 

Hummm - not sure about the oil temp sensor, if there is one. Just been out in mine to check a couple of things I sorted at the weekend which needed me to open her up a bit (past 5000 rpm) to check I have solved the P1518 fault code which I have!

Oil temp on a 20 mile round trip stayed around 1/2 to 1/3, pressure fell a bit as the block warmed up.

Difficult to find a wiring diagram for the ST170 but I haven't seen an oil temp sensor - normally on the oil filter housing. I will look when I have a chance!