Nissan Micra K11 - Coolant level dipping but no evidence of leaks

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Tue 31 May 2011 14:03
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

2001, 105k
Just passed it's MOT 3 weeks ago.

I checked the coolant level for the first time in about 6 weeks and got a shock when I noticed that the "top-up/expandion" tank was nearly bone dry. I've now topped up a couple of times and am noticing that the coolant level in tank is decreasing at a quick rate.

* I topped up to the recommended level last night.
* No level drop overnight, no drips on the garage floor. No leaks under the tank.
* Drive 20 miles to work.
* Level has dropped to Minimum.
* Radiator is still full. (Because there is still some coolant in the top-up tank, I suppose).
* No evidence of leaking hoses.
* Nothing on the floor below the car.
* Oil looks OK to me.
* No engine overheating (yet!)

Any ideas? Normally the coolant level is pretty steady on this car.

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Tue 31 May 2011 14:40
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - unthrottled

Well let's assume that it is not working its way out the exhaust!

Are any of the hoses covered in a white, sticky residue? This usually indicates a leak. Often a leak in a hose will only manifest itself when the coolant gets hot and pressurised-which won't happen idling on your drive so you don't see it.

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Tue 31 May 2011 14:42
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - unthrottled

Well let's assume that it is not working its way out the exhaust!

Are any of the hoses covered in a white, sticky residue? This usually indicates a leak. Often a leak in a hose will only manifest itself when the coolant gets hot and pressurised-which won't happen idling on your drive so you don't see it.

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Tue 31 May 2011 15:03
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

No, the hoses look OK.

To go from halfway in the reservoir to minimum in 20 miles seems to indicate a fair sized leak. If so, would have expected some drips when the car is cold.

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Tue 31 May 2011 15:18
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - Collos25
If it is not leaking then the headgasget has gone.
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Tue 31 May 2011 15:20
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - unthrottled

Sorry for double post-the site seems to be hanging' every now and then.

Any excessive white smoke from the exhaust? (Hope not!)

Does the expansion tank cap seal properly?

How much antifreeze is there in the coolant. Leaks are way easier to find with a heathy dollap of antifreeze. If you've been topping up withg water, there might not be much left. There's a leak somewhere!

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Tue 31 May 2011 15:31
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - bathtub tom

Are the carpets wet, indicating a leak in the heater?

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Tue 31 May 2011 15:35
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

No wetness in the cabin. And the heater seems to work correctly.

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Tue 31 May 2011 15:34
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

Sorry for double post-the site seems to be hanging' every now and then.

Any excessive white smoke from the exhaust? (Hope not!)

Does the expansion tank cap seal properly?

How much antifreeze is there in the coolant. Leaks are way easier to find with a heathy dollap of antifreeze. If you've been topping up withg water, there might not be much left. There's a leak somewhere!

No white smoke from the exhaust. (Would this have been picked up during the MOT emissions test?)

The tank cap seals OK. But if coolant was escaping there, it would be messy, I expect!

I've topped up with coolant the last couple of times. So that I would notice if it dripped on the floor.

Maybe I should take it out for a run, then have a look in the engine compartment while the engine is warmed up and running.

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Tue 31 May 2011 16:46
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - Ethan Edwards

On my old Corsair those symptoms were all fixed by changing the Radiator cap.

The spring had become weak with age and was rising, thus allowing coolant to escape from the relief hose. Your Micra have one of those spring Radiator caps on the expansion tank perhaps? When cold it sealed perfectly, when hot the coolant expanded and the weak spring allowed it to escape through the vent hose. A two quid replacement cap was good news as I was expecting a Head gasket like you.

Why not take it for a run and get it hot. Stop keeping it running look under the bonnet. Or you could just replace the cap.

Edited by Ethan Edwards on 31/05/2011 at 16:49

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Tue 31 May 2011 16:53
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

The expansion tank has a screw-on plastic cap. It seems sound enough.

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Tue 31 May 2011 16:59
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - Ethan Edwards

Oh OK. Sounds like a possible H/G then. A garage should be able to do a very quick cheap 'sniffer test' and confirm that without taking anything apart. It detects combustion gasses in the coolant. Uses a thing like a plastic turkey baster and some chemical.

I assume youv'e checked the oil filler cap for 'mayonaise'?

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Wed 1 Jun 2011 10:54
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004
There is no mayonaise on the oil filler cap.

The car passed it's MOT last week. Wouldn't a failed H/G cause the car to fail on emissions?

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Tue 31 May 2011 16:47
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004

Just a thought.

When I unscrew the radiator cap, there is no release of air. This is when the engine is cold.

Is this normal?

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Tue 31 May 2011 16:52
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - Ethan Edwards

I've never noticed air rushing in or out when opening up a radiator cap. By the way - Do NOT open up a hot cap ! OK.

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Tue 31 May 2011 21:41
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - unthrottled

No. When cold there shouldn't be any pressure.

Settle it for once and for all. Take the car for a drive (at least 5 miles) so it's nice and warm. When you get back keep idling until the fan comes on. Now you know the coolant is hot in the whole system. Open the bonnet and manually open the throttle so the revs rise to about 4000RPM. With the thermostat open and the engine revving the coolant will really be moving around the secondary loop. If you don't see a leak under these conditions then there isn't one-and the h/g is breached.

A small h/g leak wouldn't affect the emissions at all. A bigger one might cause HC and CO readings to rise.

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Wed 1 Jun 2011 14:10
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - madf

Examine the radiator - both sides.. VERY carefully for antifreeze deposist - colour white or coolant colour. Tubes can corrode and give way under pressure.

Have you checked the radiator is - when the engine is hot and stopped- warm /hot all the way down. A sudden cold patch = blocked radiator,

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Wed 1 Jun 2011 15:42
Nissan Micra K11 - Coolant level dipping but no evidence of leaks - mikem004
I've found the leak.

Took it out and thrashed it. Had a look underthe car as soon as I stopped.
Coolant was dripping down, from the direction of near the back of the engine compartment, centre.

There are no obvious, easily accessible hoses. So I'm taking the car in tomorrow.

Hopefully it will be just a hose!
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