Car temperature

Limey

Stuck open stat will cause the displayed temp on the dash to fluctuate, it will display cold (relatively) when the car is moving at a reasonable pace. When the car slows or comes to a standstill and the engine is left idling you will see the temp on the gauge come back up towards a more normal operating temp.

There's no other fault on a car that I know of that will cause those symptoms (always happy to be educated though).

I don't know how quickly or accurately the modern digital displays react but it should be pretty obvious.

Geodark

Gloomendoom wrote: »

Some thermostats cost an awful lot of peanuts and require half the engine to be dismantled to replace.

Yes, on my engine (Z16xe) £10+ish for the thermostat and housing, 30mins to replace it - Z16se on the other hand, around the same price for the thermo, but the timing belt etc has to come off!

reeac

IN the final line of my post no.19 I meant "over cooled" I.e. Running at too low a temp. Sorry.

Londoner_1

Car make and model??

Diesels are slow to warm up, in the current cold weather they will take longer.

Richard53

reeac wrote: »

The stat maintains the correct coolant temp by varying the time open vs the time closed taking into account ambient temp and engine power output.If a defective stat is stuck open then the engine will be undercooled which will increase wear, sludge formation and fuel consumption.

AdrianC wrote: »

It certainly will, especially a vaguely modern diesel at low ambients. The radiator will be shedding more than enough heat for the coolant temperature to quite simply never reach normal temperature or - if it does, in heavy traffic - it'll drop again very rapidly once there's more than nominal airflow over the rad.

Apologies - you are both right. In my post I was being very general to try to avoid writing an essay, and I ended up being imprecise. My bad.


Yes, a faulty or missing thermostat can cause the engine to run cool over a long run, for the reasons you state. The point I was trying (badly) to make was that I doubted very much whether that could account for an engine running at 45oC - around half its normal running temperature - hence the remark about the Ross Ice Shelf (= low ambient temps).


I based my comments on the experience of running a Land Rover n/a diesel over many months without a thermostat. It didn't affect the final running temperature in the slightest, it just took an age to get there.

Rolandtheroadie

Richard53 wrote: »

Apologies - you are both right. In my post I was being very general to try to avoid writing an essay, and I ended up being imprecise. My bad.


Yes, a faulty or missing thermostat can cause the engine to run cool over a long run, for the reasons you state. The point I was trying (badly) to make was that I doubted very much whether that could account for an engine running at 45oC - around half its normal running temperature - hence the remark about the Ross Ice Shelf (= low ambient temps).


I based my comments on the experience of running a Land Rover n/a diesel over many months without a thermostat. It didn't affect the final running temperature in the slightest, it just took an age to get there.

I based mines on 3-4 years of running the GV with one apparently seized open. Sure, on our summer holiday runs it would eventually get above 1/4 and towards a normal temperature, in winter it didnt.

Even with the radiator airflow blocked (crudely with cardboard) it didnt go up much.

Once the mod was carried out, it worked as expected.

The OP mentioned he's got a Bora Tdi. In VAG cars I've pulled the coolant temp sensor before to get the glow plugs to come on at a higher outside temperature (running on veg). I cant remember what reading I got on the temp gauge with it disconnected though, to confirm or deny the expected readings if its faulty.

OP, you could check the sensor once you've took it a run. If after 5 miles or so, switch it off and go to start again.

If the glowplug light stays on for 10-15 seconds (from memory) the sensor needs changed.

Geodark

Richard53 wrote: »

Apologies - you are both right. In my post I was being very general to try to avoid writing an essay, and I ended up being imprecise. My bad.


Yes, a faulty or missing thermostat can cause the engine to run cool over a long run, for the reasons you state. The point I was trying (badly) to make was that I doubted very much whether that could account for an engine running at 45oC - around half its normal running temperature - hence the remark about the Ross Ice Shelf (= low ambient temps).


I based my comments on the experience of running a Land Rover n/a diesel over many months without a thermostat. It didn't affect the final running temperature in the slightest, it just took an age to get there.

I have a zafira, with the z16xe engine, which are well known for over cooling. a dodgy thermo can and will stop an engine reaching running temperature. you need to keep in mind that cars these days are built to take a range of engines, all of which take different times to reach running temp. mine totally over cools due to the radiator being standard across all engine sizes and then with the thermo being dodgy it makes it worse (have replaced and this one has gone! own fault for getting from fleebay!) a thermo doesnt just open when it reaches temperature - it is supposed to close again to ensure that the correct running temperature is maintained. if it doesnt close properly then the temperature will drop too much and the engine will overcool - it has nothing to do with long runs, this can happen round the doors as mine does.