I have a 1998 Peugeot 306 D-Turbo and I am having to fill the radiator expansion tank almost once a week. I have heard that this problem could be caused by a sticking thermostat or head gasket failure. I am curious as to whether the thermostat does have a fault as the normal running temperature of the engine seems to be about 70ish and should probably be at about 90. If anybody can offer any help or similar experience i would be very grateful.
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A point that has been made before (on this forum, I think) is that a head gasket that has blown between a cylinder bore and the cooling system often causes a pressure build-up in the cooling system that remains long after the engine has been switched off.
Some time after switch-off, like first thing in the morning, remove the pressure cap before starting the engine. Is there a 'whoosh' of pressure being released? If so, this suggests a blown head gasket (or, less likely, a cracked head).
Otherwise a hidden leak might be the cause, though you ought to be seing some sign of this with such a high rate of coolant loss. Do you know if your engine has wet liners, i.e. cylinder liners that are a slip-fit in the block, as on some diesel Peugeots? If so, and the antifreeze strength and quality hasn't been maintained, the liners could have corroded at the bottom end to allow coolant to escape into the sump. If Peugeot-Citroen expert 'MM' is reading this, I trust he will put me right if what I have said is not totally correct.
Regarding the possibility of a sticking thermostat, it would have to stick in the 'open' position when it should be 'closed' for the running temperature to be low and I can't see any way that this could cause coolant loss. I wonder if the reading you are getting is wrong, perhaps due to a faulty temperature sender.
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Chris,
Dizzy is right here. The low temperature reading, if caused by a thermostat stuck open, would not cause a water loss. These engines will often run at 80 on the gauge while under little stress, 70 is a bit low.
And despite Dizzy getting into the expensive aspects so soon it's well worth thinking of the cheaper possibilities first.
So you're reporting a coolant loss...but without overheating? Yes?
And please excuse me for asking but you're not "filling" the expansion tank to the top each time? Assuming not and that this weekly loss is from Max to Min levels...
(Also in all of the following I'll assume you have checked all the coolant hoses very carefully.)
A very common problem that owners often don't spot is a radiator that is leaking at the very bottom, towards the rear and often on the nearside. The loss can be small enough to dribble down onto the body pressing under the rad and disapear without noticeable drips. Also when you stop with a hot rad the small leak will evaporate rather than drip and will be hard to see. If the radiator is less than 100% in the area I mention consider this as a serious possibility.
Next is a leaking water pump. Not uncommon to a greater or lesser extent anything over perhaps 60,000mls. Again the loss can be quite significant without any real obvious drips. However if you remove the lower timing belt cover there will be a tell-tale sign of "crusty" discharge from the bottom of the pump.
Another common leak on these is from the heater matrix inside the car. In the early stages a fair loss can exist before you notice any damp patches on the carpets. Does the car mist up more than you might expect? A very involved job to resolve!
And then we come to head gasket issues. Obviously a possibility but if you aren't suffering any overheating symptoms perhaps you'll be lucky. My opinion is that head gasket issues are minimal on these engines unless the two yearly coolant changes have been missed.
M.M
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M.M, thanks for taking us through a logical order of diagnosis. Very good point about not filling the expansion tank to the top, and I now recall your earlier warnings about the often unseen radiator problem.
I agree that was a bit early for me to talk about major stuff like corrosion (more correctly 'erosion') of the liners. However I saw this as an opportunity to remind everyone of the importance of looking after the antifreeze, especially in engines with aluminium heads, blocks and/or wet liners where its corrosion inhibitor properties are vital.
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I would go with MM's process.
The radiators on these 306's are not very good and have a tendance to corrode in the very bottom corner (by the drain tap)
I had the very same problem and found it there easy fix.
regards
H
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