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My 10 year old Litchfield Forester STi needs a bit of maintenance to sort a minor oil leak but other than that has been behaving well for the past year with regular oil top ups.

This week on the drive home I first noticed there was no heating in the car, and then the engine temperature started to spike up towards the red line. So I pulled over, let the engine cool and did some basic checks.

  • top of the radiator was cool
  • oil was low, so I topped it up as normal
  • water level in radiator overflow bottle was fine
  • carefully opening the radiator cap, no steam came out

Continued on slowly but was only getting about 400 yards before the temperature would get towards the red line again. Very occasionally I'd get a burst of warm air through the heating in the car, but then it would run cold again. Running the interior heating fans did help to cool the car faster, but again, on checking the radiator and all exposed bits of the engine block, nothing felt very hot.

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4 Answers 4

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While the other two answers were ones that were going through my head while I was waiting for the service truck to arrive, the actual problem was much simpler (although much more expensive to fix)

The engineer initially looked in the radiator coolant overflow bottle and saw it was at a sensible level, but after having a quick look at the oil dipstick he also opened up the two radiator coolant caps (one is at the radiator and one is further back towards the turbo) and the coolant level in the overflow bottle dropped, instantly.

He couldn't see any liquid in them so started pouring coolant into the radiator...

  • and it took an entire bottle! The radiator and cooling system was almost empty.

So my quick look at the coolant bottle threw me off track - the entire problem was low coolant, which is why only occasionaly would I get heat, as what little coolant there was got pumped round, and an airlock prevented me seeing it.

Sign of a good mechanic - he then followed me in his truck to the next service station, where he checked the fluids again - including dipping a finger into the coolant and tasting it, and he mentioned the taste of oil.

Root cause diagnosis - cylinder head gasket has a leak (hence my oil consumption) finally leading to water escaping from the engine block into the engine and eventually ending up empty.

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    Wait, he tasted the coolant??
    – Zaid
    Apr 8, 2016 at 14:42
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    It would have been great if he licked the dipstick to see if there was coolant in the oil.
    – DucatiKiller
    Apr 8, 2016 at 18:02
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    You could tell he was an engineer - he tasted it :-)
    – Rory Alsop
    Apr 8, 2016 at 21:39
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    I just tasted an interior component to see if it was electrified. Those of us who use all of our senses can collect more data than those of you who are inhibited by your self imposed restrictions on troubleshooting. :-) Kudos to the coolant taster.
    – Ppoggio
    Apr 9, 2016 at 19:51
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    Your engineer had obviously learned that coolant only siphons in and out of the overflow bottle if the cooling system is nearly full. Your "no heating" symptom was a good clue that the level was so low that the coolant wasn't circulating properly, but local boiling in the cylinder block occasionally pushed some hot water and/or steam into the heater and gave you a short blast of hot air.
    – alephzero
    Apr 9, 2016 at 20:57
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I am leaning toward the water pump. The cool radiator and heater core are a sign that the hot coolant is not being moved around. Coolant should always flow through the heater core while the temperature is turned to hot, regardless of the thermostat. It could also be the heater core is clogged ( or heater core valve not working) and the thermostat is stuck. It is unlikely both of these things would happen at once.

Start by flushing the coolant system. Be sure to remove the heater core lines from the block and flush the heater core separate. Make sure water can flow through freely. Same with the radiator. When you are done, install a new thermostat (they are cheap) and gasket. Top off the system. See if this helps.

If this does not help, replace the water pump. This is a big job, which is why I suggest flushing the system first. I believe the water pump is run by the timing belt on your vehicle.

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To me it sounds like your thermostat may be stuck in closed position. Hints that point to this are

no heating in the car top of the radiator was cool radiator cap, no steam came out ,

A simple test is to remove it and put it in boiling water.

I hope this solves your problem since thermostats are relativley cheap and easy to replace at home.

Here's a link with aditional methods of testing a thermostat: WikiHow Termostat Testing

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Thermostat stuck closed sounds most likely to me. Although...

I had this happen to me on an old Peugeot. I checked the thermostat, and it was open, so I went looking for other causes. Still couldn't figure it. Then I found bits of plastic in the coolant.

Turns out the thermostat housing on that Peugeotwas badly designed. The thermostat pin was pushing on a thin plastic strut, and that strut had simply snapped off. Result was that the valve didn't open and the car overheated. Peugeotclearly knew about this as a design fault, because the new thermostat housing had a much chunkier strut for the thermostat pin to push against!

Edit: Ah, just seen you've answered it yourself. Never mind. :)

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