Coolant temp dropping while driving, should I be worried?

CrankyHaus

In cold weather, 5 C or less, my temperature gauge sometimes drops slightly after I transition from motorway or high speed driving to stop start driving in traffic. This is particularly the case when the engine has not been driving for long enough on the motorway to reach 90 C, instead reaching say 80 C after 10 or 15 minutes on the motorway.

I've never seen this happen before, is it anything to be worried about?

Car's a 2011 SEAT Exeo.

Tacitus Kilgore

Oil or water temp?


Is the blower air staying warm?

CoBo55

Oil or water temperature?

CrankyHaus

Sorry lads, I thought the temp gauge on the dash was for oil. The water temp is what drops.

No appreciable difference in blower temp but temp on gauge only goes from 80 C to 60 - 70 C so it may not noticeably affect blower temp.

dmc17

CrankyHaus wrote: »

Sorry lads, I thought the temp gauge on the dash was for oil. The water temp is what drops.

No appreciable difference in blower temp but temp on gauge only goes from 80 C to 60 - 70 C so it may not noticeably affect blower temp.

Probably the thermostat is stuck and needs replacing. It can't adjust for the cold air coming into the engine whilst driving

CoBo55

Does it ever reach 90 degrees? Bang in the centre where it should be.

CrankyHaus

CoBo55 wrote: »

Does it ever reach 90 degrees? Bang in the centre where it should be.

Yeah, all the time. Maybe within 15 to 30 minutes in temps above 5 C.

Slightly longer temps below 5 C. But a decent drive without constant stop start (basically out of town driving) puts it there and it stays there.

Toyotafanboi

Thread title changed.

CoBo55

Maybe the heater is taking the heat on those short drives. A sticking thermostat normally shows as running cool on the open road with the temperature climbing to normal in town driving and the radiator fan controlling temperature. Try turning off the heater until it reaches 90 and then turning it on and see does the temperature fall back. A new thermostat would be the easiest thing to start with. Are you losing water or any other symptoms?

CrankyHaus

I'll have to check the water tank but the problem has persisted on both sides of a service in December and the mechanic flagged nothing.
I do have the heater on blast these weathers so it could be that.

Andrewf20

Might be the thermostat stuck open, If so, the temp needle should go to the middle / normal when sitting in traffic as you dont have 70mph wind chilling the radiator.

CrankyHaus

Thanks All.

CoBo I did what you said in post #9 and the temp reached 90 C with the heater off before dropping to 70 C once I put the heater on full blast. Nothing to worry about I assume. Cheers!

CoBo55

CrankyHaus wrote: »

Thanks All.

CoBo I did what you said in post #9 and the temp reached 90 C with the heater off before dropping to 70 C once I put the heater on full blast. Nothing to worry about I assume. Cheers!

What distance had you travelled when you did that? Unless it was very short the thermostat should keep the temperature at 90.

CrankyHaus

CoBo55 wrote: »

What distance had you travelled when you did that? Unless it was very short the thermostat should keep the temperature at 90.

Not long, like 8 km in 10 - 15 minutes.

CoBo55

CrankyHaus wrote: »

Not long, like 8 km in 10 - 15 minutes.

It's probably the heater demanding more heat than what's available, keep an eye on it all the same especially if there are any signs of overheating.