Hi,

 

Been using the Favorit as a daily this week, and no problems at all until this evening when it got noticeably hotter on the temp gauge.

 

No obvious loss of coolant, and the fan is working (all the time - on when engine on!).

 

I will check coolant level when the engine is cold (in the morning) and see. After that, what's best to check first? Thermostat? Water Pump?
 

Anything else? What have I forgotten?

Thanks,

Jonny

What do you mean by "noticeably hotter on the temp gauge" in deg. Celsius? Does the engine overheat on highway too?
 
The most frequent cause is a bad thermostat stuck (partially) closed. Of course there are many other causes, some simpler to fix, some not so simple. I will list them below from simple to complex.

• foreign objects in front of the radiator or radiator with clogged fins
• excessive load on the engine (dragging brakes, aggressive driving style, towing heavy weights, etc)
• coolant flow restriction (foreign objects, debris, bad thermostat)
• coolant leaks
• excessive exhaust backpressure (clogged catalytic converter, crushed exhaust pipe)
• not enough coolant flow (bad pump, slipping belt)
• bad head gasket
• bad engine lubrication

Of course some will not apply to your case. So gather more observations and try to weigh each cause.
Read this too.

Good morning,

 

Thanks so much for the reply. Covers pretty much everything, as usual.

 

The temp gauge on the dash normally sits at horizontal (or just above) and gets there after 15-20 mins of use from cold. Last night was different; it got beyond its normal very quickly and on the highway. The gauge stayed there for a while, before getting hotter again - almost up to the red section on the dial, (but not into it, or even over the gap before it).

 

I have a suspicion of a dragging brake (although its intermittent and didn't happen last night). It doesn't seem to have lost any coolant, but I haven't checked when cold yet. Engine oil is hard to measure (dipstick is snapped), but I now have another now, so will check that too. I did drive quite heavily at the start of the journey, and have never really booted the car before, but backed off once it started to run hot. There is plenty of heat from the cabin heater, which may rule our the pump - as usual, the heater is either freezing or would melt steel! The radiator fan works, but I have bypassed the sensor, which I have always suspected is malfunctioning, so the fan is just on with the ignition to be safe. The expansion tank opened with a small release of pressure, but not what I would describe as a "lot of pressure".

My first suspicion is thermostat failure and that is my first check today.

 

If the thermostat is stuck closed, is it crazy to run without one for a couple of short journeys over the weekend (8 or so miles each)? I know it's not a solution, but I was relying on having transport!

 

Thanks again,

Jonathan

If the thermostat is stuck closed, is it crazy to run without one for a couple of short journeys over the weekend (8 or so miles each)?

If the thermostat is the culprit indeed (so far your observations point to it), you can take it out completely as a temporary solution. The only drawback will be a higher fuel consumption because the engine will warm up slower.

 

A slightly open stuck thermostat could explain both the high duration for warmup from cold and the overheating on highway.

Checked coolant this morning and it was within the max/min marks, but closer to minimum. I topped it up to nearer maximum, and the first two short journeys were fine. The last short journey saw the temp gauge climb to similar levels to yesterday. Each time there was plenty of time or the engine to cool fully between journey. I will check again in the morning, but this seems to suggest a coolant leak somewhere. 

 

Additionally, I gave the top radiator hose a squeeze to check for coolant returning to the expansion tank, and it seemed fine, but the thermostat made a clunky/rattly sort of sound. 

From my experience the level of coolant in the expansion tank with engine cold should be halfway between MIN and MAX. On a hot day when the engine is warmed up the level will get closer to MAX sign. Any extra coolant added over half full level with the engine cold will end up being vented through the cap. So (for now) I wouldn't worry too much. Remove the thermostat and replace if faulty. Keep an eye under the car, in the back of the engine block and under the radiator for signs of leaking coolant.

Edited 27 August, 20169 yr by RicardoM

Well, I changed the themostat and have been using the car daily (55 miles commute in rush hours) for 10 days since.

 

Warms up nicely, then holds an acceptable temperature under all driving conditions, with small fluctuations as the thermostat does its job. No obvious coolant leaks. Job done.

 

Thanks.

Well done. Keep an eye on temp. needle anyway and make sure the pins of radiator fan thermoswitch are clean and rust free. This summer too many head gasket failures occurred due to simple overlooked maintenance jobs.