Symptoms of air trapped in cooling system?

[technostructural]

Hello all,

I recently changed my coolant, and I have a suspicion that air is trapped in the cooling system somewhere. I don't know if I am being entirely rational about this, but part of it stems from the fact that the hoses feel very squishy and "empty" when the bike is not running. Even when the bike is running, the hoses feel hot, but not very firm.

I've idled it and squeezed the bottom hose, and I've tried my best to knead any air out. When running, all of the hoses seem to get hot, but they still don't feel very firm. Is this normal? I know in my VW Golf, the coolant hoses will become both warm and firm. Just to clarify any potential questions, my overflow tank is between minimum and maximum (where it should be).

Are there any obvious symptoms of air being trapped in the cooling system that I could be looking for? I just want to be sure that it is circulating properly before going on any substantial ride. I suppose my fear here is that the temperature sensor is the point of the air bubble, and I am not getting a correct temperature reading. My k75 regrettably doesn't have a gauge, just a "holy shit, too hot" light.

I should note that the overflow tank has not changed in level, even after running and stopping several times. The coolant hose that connects the overflow tank to the filler pipe also has not become hot (so presumably coolant is not actually overflowing into it).

[Scott_]

Another issue you could have would be the pressure cap, it could be week(or the gaskets bad) and not allowing the overflow system to work properly.

[Laitch]

The air bubble-over-the-sesnsor scenario you've described is pretty far-fetched.

You don't need a gauge if you've got a working warning light system and a working fan. To learn if the fan works, ride the bike until it warms up then idle it for ten minutes or so. Either your fan will turn on if it works or the temperature light will turn on because the bike is starting to overheat. That should raise the level on the gauge in the overflow tank.

If the fan actually works but is not cycling inappropriately, if the overheating light actually works but is not lit, why the worrying? Consider riding the bike more and fondling the hoses less. If your warning light turns on, shut the engine down, wait a few minutes, ride home then do the whole blasted draining and refilling procedure according to johnny.

[technostructural]

Thanks all.

Kind of a bummer that (other than the overflow tank) there isn't really a way to determining coolant level. I know that in automotive applications, the coolant reservoir is at the top of the system, so its level (assuming there are no air bubbles) is indicative of the overall coolant level. Given that the filling pipe / radiator on the K bike is above the expansion/overflow tank, it seems that we can't really rely on that as much.

Anyhow, I digress. I did take it for a short (5km) ride, and nothing seemed to have changed. I also let it idle for quite a while after that, and neither the temperature light came on nor did the fan engage. (I've recently replaced the fan with the Spal mod, so I don't think it is seized).

I will take it for a bit of a longer ride to see what happens. Draining the coolant and filling again would be a bit of a pain, but I suppose with the tank off, I could get around to changing a few rubber bits that I have been putting off.

I will let you know how it goes. Thanks for your help.

[K1300S]

How old are the hoses?  Age makes them soft.  Replace.

[technostructural]

The hoses themselves are actually in pretty good shape. I have seen far, far worse on cars.

When I say soft, I don't mean that the hose itself feels soft, but rather that there doesn't feel to be much pressure built up inside of them (even when hot).

[Laitch]

All I want from my bike's coolant is circulation. If it's only triggering the fan in traffic, I'm happy. I want pressure from a fire hose.

[technostructural]

I definitely understand what you mean by that, but air trapped in the system can prevent proper circulation. That is really my only concern.

Point taken though. I will get back to you all with my findings.

[Laitch]

If the bike's performance can't be believed, it's time to break out the endoscope.

[technostructural]

So, after riding the bike for about 150kms, everything seems to be fine.

I guess that's just how these coolant hoses feel. When cold, the coolant reservoir sits at about mid-way between low and high, and when hot, it is closer to the high mark.

Yesterday I went on a fairly long ride in hot weather and the temperature light did not come on. So far so good. I think the best advice was to "consider riding more and fondling hoses less".

Thanks all. :2thumbup:

[ATXBill]

Hey, this is an old thread but I was wondering if you had any reoccurrence of the light coming on or overheating?  I have a very low mileage (1,000m) '90 K75s and am experiencing overheating.  I've replaced the thermostat, radiator and reservoir caps, o-ring and of course, fluid.  Fan kicks on as it should and blows strongly...sounds fine.  But after about 3-4 minutes of the fan being on, the temp light comes on. 

[Laitch]

Hey, this is an old thread but I was wondering if you had any reoccurrence of the light coming on or overheating?  I have a very low mileage (1,000m) '90 K75s and am experiencing overheating.  I've replaced the thermostat, radiator and reservoir caps, o-ring and of course, fluid.  Fan kicks on as it should and blows strongly...sounds fine.  But after about 3-4 minutes of the fan being on, the temp light comes on.

This is probably being caused by lack of sufficient coolant in the system. Coolant must be added to the radiator slowly, the engine allowed to warm up and then more coolant slowly added. This method allows air to migrate out of the system. The cap is closed when the level is at maximum with time allowed for air to exit, then the reservoir is filled to reach a level between Max and Min. What type of coolant did you use, what type of water was mixed with it, and at what ratio?

Start with this simple method. You can deal with the oil/coolant pump later, if this doesn't work.

[ATXBill]

This is probably being caused by lack of sufficient coolant in the system. Coolant must be added to the radiator slowly, the engine allowed to warm up and then more coolant slowly added. This method allows air to migrate out of the system. The cap is closed when the level is at maximum with time allowed for air to exit, then the reservoir is filled to reach a level between Max and Min. What type of coolant did you use, what type of water was mixed with it, and at what ratio?

Start with this simple method. You can deal with the oil/coolant pump later, if this doesn't work.

Brand new Motul Motocool Expert Coolant, installed by a BMW certified mechanic.  Reservoir level was right in-between MIN & MAX.  Rode it 150 miles today.  First 125 miles were no problem, though a lot of higher speed highway miles.  When I went into some twisties at slower speeds (35-40mph), that's when the problems began. I pulled over 4x and let it cool down before riding again.  Problem repeated within 10 minutes each time.  Got home, let it cool off for an hour.  Started it and idled for about 8 minutes before the fan kicked on. After about 3 minutes of fan, the temp light came on again.  Fluid level in reservoir hasn't deviated.

[alexg]

Search on this forum for “strange overheating conditions “. Your symptoms are very similar to the one problem I had. Filler cap check valve stuck.


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[ATXBill]

Search on this forum for “strange overheating conditions “. Your symptoms are very similar to the one problem I had. Filler cap check valve stuck.

Thanks Alexg. I had the filler cap replaced. Is the check valve a separate part or embedded in the cap?  I'll do the search you mentioned...thanks again for the quick reply!

[Laitch]

Fluid level in reservoir hasn't deviated.

I think the problem is lack of fluid in the radiator, not the level of coolant in the reservoir. It's simple enough to check it if you know how and there is a manual on this site for reference. It doesn't matter who is certified in what if they're not attentive to details or don't take time enough for the procedure.

On the other hand, you can always hope it's something serious or mysterious. :giggles  Maybe it's an ancestral curse.  :yow

[johnny]

greetings...

drain it and measure in the coolant this time... slow and burp... its the only way now...

j o

[rbm]

Burp the system by repeatedly squeezing the coolant hose where it exits the crankcase cover and bends to meet the water pump.  Do this after re-filing before starting and while the engine is running.

[stokester]

This is probably being caused by lack of sufficient coolant in the system. Coolant must be added to the radiator slowly, the engine allowed to warm up and then more coolant slowly added. This method allows air to migrate out of the system. The cap is closed when the level is at maximum with time allowed for air to exit, then the reservoir is filled to reach a level between Max and Min. What type of coolant did you use, what type of water was mixed with it, and at what ratio?

Start with this simple method. You can deal with the oil/coolant pump later, if this doesn't work.

This is the way I do it and have never had an issue.