Rad fan weird behaviour

[MK21800]

This is I guess halfway linked to my coolant thread :

viewtopic.php?f=9&t=19914

Although I must admit, since giving the jubilee clip (luckily it was one of those not a spring clip) a little nip on the bottom hose, I don't seem to be leaking coolant anymore, who knows.

Weird behaviour was earlier - I refilled a bit of coolant from the min mark to the max mark, and left the engine running with the cap off, let the water heat up a bit, then put cap on. I understood this helps prevent air locks. Is this the wrong thing to do?

So all's cool, then I'm sitting in a traffic jam shortly afterwards, and my temperature starts to rise. It gets to just below the first white line on the right, then I just break free of the traffic jam in time, and temperature cools down with free driving.

When I get home, I leave the car running - and discover the fan's not kicking in. So I stop the car before it overheats, and ten seconds after I stop the car, the fan kicks in. Eh?

Start the car again, fan seems to be working now. Possible I have some kind of air lock or something? Do I need to bleed it? Sticky thermostat?

Probably something blindingly obvious to you fellas, I trust. It is in fact a relatively new rad fan, as it goes, so I don't think it's the fan itself.

Also, although I'm not sure about this, when I refill to the max mark in the header tank, it seems to gradually go down to the min mark and then kind of stay there over a period of time. Then it doesn't drop below the min mark and seems stable at that point.

[MK21800]

Yeah did it again just now - reached about 70% and the fan didn't come on.

When it's hot, both hoses are hot, indicating to me that the thermostat is fine. Pretty sure the rad fan is fine. Might try jumping it tomorrow to check it's not suddenly bust, although like I say, it's relatively new.

I'm thinking - perhaps it's the thermoswitch in the top of the engine?

[unknownmale]

Sounds like a switch to me, but also worth checking the connection to the fan also for corrosion and continuity

[MK21800]

Cheers unknownmale,

I actually think I mean the thermoswitch ad the bottom of the rad (what am I thinking of at the top of the engine? Never mind).

I've found an article on how to test the fan and the switch.

The car has been sat for the best part of a year (with ocassional start ups) - I wonder whether the thermoswitch has stuck.

I'll test and report back, spotlight on thermoswitch at bottom of rad currently I think.

[mark1gls]

If the thermostat is stuck shut you wont get any hot coolant in the bottom radiator hose, start the car and let it run the bottom hose should be the last one to get hot.

[MK21800]

Ok just did some tests -

Pulled the connector off the thermoswitch at the bottom of the rad, jumped it, fan came on. Conclusion - fan ok.

On warm-up, the top hose goes hot pretty quick, then the bottom hose goes hot when engine gets warm. Conclusion - thermostat ok.

So I'm thinking "Ok, it must be the thermoswitch itself" - about to turn the car off and the fan comes on by itself while the car's running. I let it run, it turns off, then I let it run still and it comes on again. Perfectly as it should, keeping temp to about 40%.

So couldn't reproduce the problem today. Any ideas? The only clue I have is that yesterday the fan didn't turn on straight after refilling coolant. Could it be something to do with an air lock or something? Or perhaps when I pulled off the connector to the thermoswitch and put it back on, perhaps there was a bit of grit in there or something. Or indeed with the fan connector.

Don't get me wrong, I'm pleased, but it does make me a bit edgy having an intermittent fan problem.

[MK21800]

The fan's been running fine since the above post, however -

I degreased the engine earlier, and although she started fine afterwards, again the rad fan didn't come on. Stopped the engine at 70% heat (normally it will only reach 50% then the fan comes on), went in the house, came out to find the rad fan going! (As they do when the car's off).

Started her up again, now the fan works fine.

Seems like anytime I do anything to this car, the rad fan throws a wobbly the first time I start her up. Wonder whether I got the thermoswitch connector wet when I hosed the engine down, or something.

What kind of voodoo is this?

[MK21800]

Hmmm... it did it again earlier, it's been fine, and I was driving it today, and could hear the fan coming on at points, everything ok.

Then pulled into my drive, and noticed the temp was rising again and the fan hadn't cut in.

Turned car off, switched back on again 30 seconds later, and the fan cut in!

Hold up - Do I remember there's a fan fuse and relay? Now it wouldn't be the fuse, I woudl have thought otherwise it wouldn't work at all. Could what I have be a symptom of a relay that sometimes sticks? Any way of testing it?

Everything else about the cooling system seems fine, no coolant loss, thermostat working, fan works if I jump it. Just seems that 99 times out of 100 it cuts in, but there's the odd time that it fails.

[MK21800]

Sorted! I think.

Drained coolant from rad and took thermostat out from block, got about 5 - 5.5 litres out.

Tested thermostat. Ok.

Flushed system. Not too bad but little bit of brown water.

Put back together again, new Meyle radiator fan switch, better than the dodgy looking unbranded one I had in there. Putting this in was loads of fun from beneath the car using vice grips. A hillbilly moment. I'm afraid my toolkit doesn't yet extend to 29mm ring ratchet spanners, which would have been a luxury.

Put in new o-ring for stat. Assembled back togather. Again, loads of fun trying to line everything up when it's upside down, stat keeps slipping. But got there in the end (poke finger through elbow joint). Thought about new stat, but this one's always been kind to me so decided to keep.

Put in fresh load of blue premixed 50/50 Europarts QX antifreeze like foks on here always recommend. Great price!

Started her up without expansion cap on, ran, revved, noticed constant feedback through return hose at about 2000rpm , squeezed a couple of hoses (I don't think we really need to do this as they're kind of self-bleeding, no?) noticed coolant alternating between about 45% and 50% - good stat. Put cap back on when temp was about 30% before coolant boiled. Booted it, rad fan came on, went off, came on again. A very welcome sound.

Expected all kinds of coolant waterfalls due to doing something wrong, but no, dry as a bone from the stat housing, rad pipes, and rad fan switch. No coolant loss from header tank after 20 mins running.

Will test drive properly tomorrow.

Coolant is only at min though currently, knew I should have bought a litre or so more coolant, need to top up slightly but it's not losing any. Will order.

I'm happy with that so far so good! Got a bit of experience with that job. Shut bonnet on vape pen at the last minute, and bent clearomiser, but you know - no one bats a thousand.

Does that sound about right? Anything I drastically missed?