Thread: Low engine temp reading.

Here is today's puzzle. I drove Sydney to Canberra early Tuesday morning, leaving at 0500.* I had covered about 70km before the temperature needle got to the horizontal.* It wavered a bit before settling (never wavering above the horizontal at all).* After about 2 hours I stopped for a very short pit stop, according to the SatNav I was stationary for less than 2 mins.* When I set off again the needle dropped to just above the cold and took a long time to get back up, as soon as I left the freeway and below 100kph it fell again.*

Data for the trip:* distance - 320km, average speed 105km, fuel consumption - 9.8l/km.* I looked under the bonnet when I arrived and everything was as it should be, no steam, no loss of coolant - nothing.*Outside Temps SYD 12C CAN 6C.* Engine seems fine, plenty of power.

I few thoughts

• It's the first time the new(isn), and therefore more efficient, radiator has encountered such cold temperatures, it could just be how it goes.
• Thermostat could be jammed open but that would*only account for a small*drop in temperature after the pitstop and it should have gone straight back up.
• Thermostat could be jammed shut but surely I would have trashed the engine?
• Air lock, but I squeezed all the reachable hoses and they were all full of coolant
• Dodgy sensor
• Dodgy instrument

SWMBO has put Daisy on warning to buck her ideas up so I need to get to the bottom of this pronto.

Hi, typical open stat symptom IMO, it's possible that due to the open stat the gauge went to the middle but the temperature was very close to the quarter position temp. and during the stop it dropped just enough for the gauge to go to the quarter mark...then it will take some time to rise back cos with opened stat at lower than normal temperature especially if you move faster or rev it harder the coolant will be cooled continuosly.

replace the stat before you do anything else... when you refill the system fiollow this procedure: unclip and lift the tank above the bleed hole, fill untill a clean flow comes out there, then refit the tank, put back partially the bleed screw, ask somebody to keep revs above 1500rpm(for the bypass valve to stay open) tighten the bleed screw when no bubbles are showing around it...job done

BUT... just to rule it out and to be on the safe side, if you know that the temp sensor is very old replace it with a new genuine one...i can tell you from my experience(and i have plenty) that these NTC sensors are loosing qualities in time and even if they work they might give erratic outputs... it's a good prectice to replace the temp sensors(coolant and fuel cos they're the same) after let's say 50K miles, even better 50.000km, it's demonstrated that they can affect consumption and fueling without even noticeing it cos teh gauge is very "permissive"...it goes from quarter to the middle at just above 70*C and higher at 115*C ..the optimal temp for a Td5 engine is 90*C so if the sensor is old it will read lower and even if the real temperature is 90*C the management will work for let's say for the 75*C reading which means overfueling.

now i hope your's it's not a V8... albeit this theory is valid for V8 too but at other temperatures