Temp gauge dropping!

Went out for a 3 hour ride yesterday, mainly motorway riding and then 'A' road and town riding for the last hour.

Occasional glancing at the gauges and lights during the ride all showed normal until about 1 minute from home when I noticed that the temp gauge had dropped to two bars. When I stopped outside my garage (engine still running) the gauge popped back up to three bars straight away, back to normal.

What on earth could cause the engine temperature to 'drop' while riding? The ambient air temperature was about 10 degrees but I've ridden in minus temperatures many times and the temp gauge has never moved.

Any ideas

Sticking open thermostat?

Good point oldwingguy and I hope it is something fairly simple like that. I always thought that once a thermostat was 'open' after a cold start that it would just stay open until the engine cools right down after stopping.??

Does a thermostat open and close during riding? I have never thought about that, till now.

Loosemarbles wrote:

Good point oldwingguy and I hope it is something fairly simple like that. I always thought that once a thermostat was 'open' after a cold start that it would just stay open until the engine cools right down after stopping.??

Does a thermostat open and close during riding? I have never thought about that, till now.

I too would have thought that but it's mechanical so all bets are off The cooling fan acting normally? It cycles as we know.

Mmmmmmm.......cooling fan? I suppose if it was running when not needed it would cool the system prematurely. I'll make that my first investigation. Weather here is not looking too good for the next few days so I'll wait till it improves.

Whilst on the subject of the fan I have previously considered installing a dash light to show when the fan is running rather than trying to listen for it. Shouldn't be too difficult to do.

oldwingguy is most likely right. Thermostats do go bad they start to hang up a little open or don't open at all. Honda makes good parts but they do wear out.

Fan running all the time would not cool the engine if thermostat was working correctly. It opens and closes but slowly as coolant heats or cools it. Once you stopped no airflow through the radiator temps. came back up. Replace it. I hope that's 10° C not F. Burrrr.

Hi to all,
I started experiencing the temperature drop, and figured the the thermostat was not opening-closing properly
Last weekend I changed it, but the the issue remains!!
The thermostat is original Honda part
Maybe the problem is with the gauge?
Any ideas?
BTW, to reach the thermostat I had to remove the central cover, though the service manual only mentions the left side cover; did I miss something?
Regards from Madrid
Eduardo

.

Replacing the thermostat fixed my issue with engine temperature dropping but efinglada has already tried that. BTW, I managed to change the thermostat without removing the central cover.

My only other thought is that the fan is kicking-in when not needed which would suggest faulty thermosensor or fan motor relay. But if mech1twa is right, this wouldn't cause the engine temperature to drop.

As for a faulty temperature gauge? IMO unlikely. This is certainly a curious mystery.

efinglada, is your temperature dropping while riding and does it alter with different riding conditions etc?

The fan works ok, with engine running without moving the bike it will start
While riding the gauge has always shown 3 bars. Now temperature drops to 2 bars while slowing for a while, ie going downhill or reducing speed
It would be very unlikely that I got a new faulty thermostat

What was the temperature outside when you were running? Im on my third wing and have never experienced that. Once the bike warms up it at 3 bars. Riden in 30 degree weather and never dropped. Riden in 100 degree weather and never dropped. I will be interested in what you find out.

I have the SW since 2 years ago and the temperature issue started two months ago, my driving conditions through the year range from -5 to 40 degrees Celsius (23 to 104 F)
Riding this morning with 50 F, the temp dropped...
The only reason for this should be a faulty thermostat. I will ask the Honda mechanic if they have experienced this before
I will come back with the findings

I have a suggestion: Why not present this problem to the legendary Stefano Bonacasa at his Face Book Silverwing SW-T forum (https://www.facebook.com/groups/hondaswt/). Someone there, if not The Maestro himself, may well share more information and help resolve this perplexing condition.

It should be easy enough to do a basic function check on the thermostat without any bike surgery. It should stay closed until the coolant in the engine exceeds the opening point of about 78C.

If you start the engine from cold and keep your hand on the radiator, you should find that it stays cold for a few minutes, and then quickly gets too hot to touch, which indicates normal thermostat operation.

If on the other (unburned) hand the radiator slowly but steadily heats up from cold engine start, then it is stuck partially open and should be replaced.

Thanks for the replies,
I will do the hot radiator test first
Honda mechanic told me to clean-flush the circuit with a radiator additive, in case deposits are preventing the thermostat from closing fully; next would be to check the temperature probe
I will also try to get the opinion from Bonacasa
Regards

If you do the flush rinse the last of it with distilled water, then replace the antifreeze with premixed or use the concentrate 50/50 with distilled water.

DI'd the hand-on-radiator test and I felt the temperature rise fast, I think.....never done it before
Next I will flush the circuit and see what happens

It's been my understanding that the thermostat should keep the engine at the temperature that it is rated at +- 5 deg or so. To test the thermostat remove it. Take it in the house and put it in a pot of water on the stove along with a temp gauge. Watch it open as the water heats and note the temp. Proof positive if it is working correctly.

I tested the thermostat I removed as defective in hot water and it opens-closes ok, so the problem must be the water temperature sensor
I will flush the circuit, just in case there are deposits.....

Some ideas/Suggestions...

Since you ruled out the thermostat, it could be the temp. sensor itself, bad /dirty connector or poor contact/grounding of the sensor body to engine fitting. Before you remove the sensor check for a good ground/continuity between the sensor brass body and a frame ground, sometimes dissimilar metals (aluminum and brass) corrosion causes poor contact. Remove the sensor and clean threads well, apply a light coat of sealant or several wraps of Teflon tape to threads only when installing, you want good contact between sensor nut and engine housing, while sensor is out test per Service Manual 21-16, when you do the bleed procedure, repeat it a few times after allowing bike to cool, the sensor is at the highest point on engine, air could be trapped there.

Thanks for the tips ZRX, I see that I will have to remove the luggage box...so it will be sometime before I can do it

I flushed and rinsed the circuit and the temperature still drops......
I sent a message to Stefano Bonacasa and replied that he had not encountered this issue ever
Next check will be the sensor.....?

Sorry that you're having so much trouble with this. There is always the possibility that the new thermostat is faulty....very unlikely but not impossible.

The sensor assembly is not too expensive but it is awkward to get at. Please let us know how you get on.