Hi there I’m wondering if anyone can she some Light on this I have 64 1.6 diesel Ford Focus Christmas time it had temperature problems which turn out to be a warped block so I had the engine replaced now the car runs fine get up to temp doesn’t over heat but as soon as I turn the heaters on hot the temp gradually decreases its had 2 thermostat and only happens when heater is in hot position and fans on 3-4 the heater works fine just a bit of pain 

Totally normal on diesels, especially the 1.6TDCi.  The cabin heater uses hot coolant from the engine, with the fans on full, they take heat out of the coolant more quickly than the engine can heat it again.

 

So it’s normal for it to decrease all that way down to 60-70

11 minutes ago, TomsFocus said:

Totally normal on diesels, especially the 1.6TDCi.  The cabin heater uses hot coolant from the engine, with the fans on full, they take heat out of the coolant more quickly than the engine can heat it again.

 

So it normal for it to cool down to 60-70

The guage isn't live, it's not as cold as it looks but yes it'll cool it to around 75c if you check with an OBD reader.  The stat will close around 80c but with the cabin fans on full it still won't be able to produce enough heat.

Completely normal.

The heater simply draws more heat from the cooling system than the engine produces. This is the downside of modern efficient diesel (and also petrol) engines. This is also the reason why many modern cars have an electric heating element inside the coolant system to increase the coolant temperature or an additional electric heater element inside the heater housing to heat up the cabin. 

1 hour ago, TomsFocus said:

The guage isn't live, it's not as cold as it looks but yes it'll cool it to around 75c if you check with an OBD reader.  The stat will close around 80c but with the cabin fans on full it still won't be able to produce enough heat.

I have the live reading and it drops below 75

I remember the old school trick if your car was over heating in the summer. wack the heaters on full to release all that heat!

 

So  it completely normal for the temp to drop back down to 60 in this heat?

?

In what heat, exactly? Kents? If it's about 15C outside, I would not consider it completely normal. If you drive a lot of city traffic then the engine will stay cooler, however.

My 2018 1.5 TDCi can hold it's temperature here in Finland if outside is above 5C (if driving outside cities), yet alone above in above 15C ambient temps.

I would have those thermostats checked or replaced, I believe you have two thermostats in your engine as well?

Also check if you have the active shutter grill in your model, and whether it works properly.

An "Active Shutter Grille" - People use to stick cardboard in front of their radiators in winter and I can remember radiator blinds that worked on a piece of string !  Cheap, and the string was reliable and repairable - not so sure about an  "Active Shutter Grille" - probably needs a dealer visit to scan for a fault code, and then replace an expensive component.

The active grill is mostly for better aerodynamics at speed although it does help warm up times as well.  When closed, air flows smoothly over the front end at 70mph instead of being spoilt through the engine compartment and causing extra resistance.

If the temp is dropping to 60c the stat should be well closed by then so the grill will have very little effect on engine temps unless the stat is stuck open, but then it wouldn't warm up in the first place.  Were they genuine stats that you had fitted or just cheap aftermarket ones?  Is the problem exactly the same as it was with the original stat?

60c does seem overly cool for this weather I agree, but then I've never tested the heaters on full in summer lol, it wouldn't be unusual for town traffic in winter.  

 

The grill is actually for cold environments also, I managed fine with it on my earlier Focus for three years, with temperatures dropping to -32C at the lowest.

I’ve had thermostat replaced twice it only occurs with heater on Hot it has been scanned no codes

After market stat and no the problem before hand was different 

19 hours ago, TomsFocus said:

The active grill is mostly for better aerodynamics at speed although it does help warm up times as well.  When closed, air flows smoothly over the front end at 70mph instead of being spoilt through the engine compartment and causing extra resistance.

If the temp is dropping to 60c the stat should be well closed by then so the grill will have very little effect on engine temps unless the stat is stuck open, but then it wouldn't warm up in the first place.  Were they genuine stats that you had fitted or just cheap aftermarket ones?  Is the problem exactly the same as it was with the original stat?

60c does seem overly cool for this weather I agree, but then I've never tested the heaters on full in summer lol, it wouldn't be unusual for town traffic in winter.  

 

 

After market stat and no the problem before hand was different 

20 hours ago, TomsFocus said:

The active grill is mostly for better aerodynamics at speed although it does help warm up times as well.  When closed, air flows smoothly over the front end at 70mph instead of being spoilt through the engine compartment and causing extra resistance.

If the temp is dropping to 60c the stat should be well closed by then so the grill will have very little effect on engine temps unless the stat is stuck open, but then it wouldn't warm up in the first place.  Were they genuine stats that you had fitted or just cheap aftermarket ones?  Is the problem exactly the same as it was with the original stat?

60c does seem overly cool for this weather I agree, but then I've never tested the heaters on full in summer lol, it wouldn't be unusual for town traffic in winter.  

 

 

I also forgot to say this only happens at idle 

49 minutes ago, Mc8696 said:

After market stat and no the problem before hand was different 

 

Well there's the issue then...  Buy cheap, buy twice!  

The stat has been replaced twice in 3 weeks?

13 minutes ago, Mc8696 said:

The stat has been replaced twice in 3 weeks?

I feel like we're going round in circles here lol.

You say the problem was different before the stats were replaced right?  Both times, the stats were just aftermarket rubbish instead of the genuine items? 

If so, buy a genuine stat...they are of higher quality and with tighter tolerances than the aftermarket parts.  Meaning the aftermarket stat is likely to be a bit lazy and not close as quickly as we'd like.  As said, it's totally normal for the temp to drop under those conditions anyway, so a poor quality stat will only make the issue worse.

We’re is a the best place to buy a genuinely stat     

 

I note towards the end it says this only happens at idle. I had a 1.6tdci which I owned from 1,600 miles to 146,000 miles. On that the temp gauge would start going down if idling with heater on. At idle the engine is creating so little heat the heater is taking more heat out of the coolant than the engine is putting in on these very efficient engines

That is why there is the additional electrical heater system. This system consist of an electric heater element that is installed inside the heater housing assembly. When the engine temperature is below a certain value the electric heater element is activated to heat the interior.

This has several major advantages. The engine will warm up much faster because the amount of heat from the cooling system that is used to heat the interior is drastically reduced. The extra load to the alternator to power the electric heater element also contributes to a faster warm up of the engine. Finally the additional electric heater system is great because the interior is warming up almost instantly when the engine is started (even when completely cold and low ambient temperatures).

For most cold climate markets the additional electric heater system is installed as standard on Focus MK3/MK3.5 vehicles with Diesel engines and some Petrol engines (1.0 ECOboost). Each market has the ability to change vehicle specifications. Because of this the specifications are different for each market. To reduce costs most medium and hot climate markets do not have the additional electric heater system installed as standard. In some markets this option was not even available.

On the MK3.5 some engine types did have the additional electrical heater system fitted as standard as a measure to meet the emission regulations. The considerably faster warm-up time of the engine reduces emissions.

Here in Finland all Focus Mk4 diesel cars have a factory-installed auxiliary heater, that's integrated to the car's control system

https://www.webasto-comfort.com/en-uk/product-overview/product/show/thermo-top-evo/