Overheating - time for a rebuild?

[Filmcamera]

I hope I do not know the answer to this question already but fear I might.


My 1991 16v K100RS has been back on the road for about two years now.  I ride it fairly often and fairly hard.  Yesterday for example I did 150 miles to the beach and back on mountain roads over four hours or so.  All in all I average around 500 miles a month.


It has always ran a little hot, something I put down to be in Costa Rica where is it seldom less than 27 C or 80 F and humid.  There is also always quite a lot of slowish speed twisties and climbs through mountains etc.


It has also always used a lot of oil.  Take yesterday's ride for example, I checked the oil level and it was bang in the middle before I left.  When I checked again this morning it was just touching the bottom of the sight glass, what is that 3 fl oz?


Now the issue at hand.  It seems to be running hotter and hotter.  At least half the time yesterday the needle was just below the red, the kind of temp where the fan would kick in if it was not already on from the manual switch I have.  Without the fan it would boil for sure, with it it JUST stays out of the red.  The funny thing is that maybe one ride in three is stays just above half or maybe just below 3/4 the whole time with no issues except when doing a long slow climb when it will rise but then come back down again as soon as I have a few minutes of sustained speeds of 50 mph+.  On the way back from the beach yesterday it absolutely poured with rain, a real torrential downpour, the first time I have ridden in raid that bad and I have to say I was very impressed with how sable the bike was and how (relatively) dry I stayed.  Needless to say the engine temp was fine all the way home since it was getting a nice soaking!


Here are the things I have done to try and remedy the problem so far.


New thermostat, I soaked the radiator in vinegar for fours days before flushing carefully and refilling with racing coolant. The temperature sensor is also new as is the oil sensor.  The radiator itself seems in good condition.


So what else can I try? Are there any other options apart from and engine rebuild with new rings etc? Could there be an issue with the oil/water pump? (I have never touched that since I got the bike).


Last piece of info is that when I checked the valves they were nearly all a little tight, I have not fixed that as of it.


Riding season is just arriving here and I really do not want to take if off the road for months to strip the engine down, not to mention the cost, especially since I would have to buy a bunch of special tools from what I can see.

[Martin]

FC what was the condition of the water when you first drained the radiator. Sometimes vinegar won't shift all the scale and what scale it loosens can end up clogging the galleries. A compatible proprietary cleaner along with reverse flushing is sometimes needed or have it professionally cleaned and checked.  You also need to remove the thermostat and check that it's fully opening. Just because it's new doesn't mean that it is working correctly. A corroded impellor vane in the pump will allow it to over heat as will a impellor slipping on the shaft as it heats up. What was the brand and specifications of your coolant. Long shot incorrect ignition timing will also cause it to run hot as will too lean a mixture. Do your valve clearances.
Regards Martin.

[Martin]

FC you might also want to check that your temperature gauge is calibrated correctly. I have seen a few people chasing supposed problems when all that was wrong was a gauge or test equipment reading wrong. I had a car with a standard temperature gauge that read high. I fitted an auxillary temperature gauge and it read low. I took both into work and had them recalibrated. Are you using coolant?
Regards Martin.

[Filmcamera]

Hi Martin,


The coolant is Bel-Ray moto chill racing coolant. This is some of their blurb


Bel-Ray® Moto Chill Racing Coolant is an engine coolant that uses a special non-toxic propylene glycol formula designed for better heat transfer and cooler running engines. Protects from corrosion and extends the life of all motorcycle cooling systems including those using magnesium and aluminum components

The water that came out of the radiator was not too bad, I had already flushed the radiator with just water a number of times when I got the bike, I had also squeezed the tubes multiple times because they sounded 'crunchy' when I first got the bike.  After the vinegar soak I flushed the radiator a few times with water but will take your advice and see if I can find a special cleaner to try again.  There are no professionals for that kind of thing here I am afraid.


I will also check the thermostat.  I can check the valve clearances again but fixing them is a pain on the 16V bikes, if I have to do that I might do the whole thing and do the rings at the same time.


Do you think I should crack open  the water and oil cover to have a look at it then?


The bike doesn't run lean if anything it runs rich.

[Filmcamera]

The coolant is supposed to be used undiluted but I diluted it, partly because it is so damn expensive here, $30 a liter. Originally I had it 50/50 and this time after doing the vinegar etc I went 2/3 collant 1/3 distilled water.

[Laitch]

The radiator itself seems in good condition.
So what else can I try?
Last piece of info is that when I checked the valves they were nearly all a little tight, I have not fixed that as of it.

The coolant is supposed to be used undiluted but I diluted it, partly because it is so damn expensive here, $30 a liter. Originally I had it 50/50 and this time after doing the vinegar etc I went 2/3 collant 1/3 distilled water.

An engine shouldn't be run with tight exhaust valves regardless of whether they're a little tight. All valves should be set to spec. It's a more complex process in a 16V moto but it must be done.  Brichbk's thread shows what can happen when valve clearances are ignored.

The moto isn't overheating until the temperature light is lit. On a long, slow mountain ascent, the engine will be warmer than on the flats. Even with the fan operating, the gauge will be toward its upper range. I'd like to know if the fan cycles when you don't have it activated by the bypass switch. Try flipping the radiator cap gasket to perhaps seal it better. If it isn't sealing well, the boiling point of the coolant is lowered. Your moto should work well with long-life coolant in a ratio of 60% distilled water:40% coolant. How does your racing coolant differ from long-life?

As far as oil consumption goes, according to BMW, maximum permissible oil consumption is 1.5 liters per 1000kms. Of course, some motos consume less than others, but thou shalt not covet.  :oldguy:

Don't let your imagination run wild. Adjust the valves; flip the radiator cap gasket. Verify the coolant level. Follow manufactuers' instructions. Your cost-cutting and avoidance of maintenance can lead to the parting out of your moto.

[Filmcamera]

Yes the fan does come on automatically if I do not have it manually turned on.  I will try leaving it to do its thing and see if it turns OFF as well and how often.  The coolant level if fine, I just checked it.  I will flip the radiator cap to see if that helps.


I have no idea what the difference is between long life and racing coolant, here you have limited choices to say the least and that seemed to be the best option I could find.

I guess this weekend I will be rechecking the valves and seeing how they are, first though I am off to see Roger Waters in concert tomorrow night with my two sons. I can't wait!

[Martin]

When I flush radiators I try to run it through a cloth. A cloth can be cable tied over the inlet pipe forming a bag so that you can see if there is any scale. If your hoses sounded crunchy it would more than likely be scale. When you flush it is better to reverse flush as this stands more chance of dislodging scale. Forward flushing can result in pushing scale into the galleries. Previously you just cleaned the radiator I would in order  first use a compatible cleaner and run the bike the required amount of time then reverse flush and check what is in the water being flushed out of the radiator and the block. If scale ,crap or debris is encountered I'd do it again.  The water in both the block and the radiator needs to run clear. Scale coating the inside surface of the block inhibits the transference of heat from the block to the water, and can lead to overheating.  I would also check to see if the cooling fins are clear of bugs and crap. Do not use air or high pressure water to clean the cooling fins. Bent cooling fins need to be straightened gently. There are tools available cheaply of Ebay or use popsicle sticks cut and sanded to size , don't use anything sharp. If there was signs of corrosion in the water I would pull the pump to check for corrosion. For peace of mind you might want to check the impellor. Electronic immersible thermometers are available from Ebay and can be used to test the gauge and the thermostat as well as checking your coffee. Are there signs of leakage at the weep hole.
Regards Martin.

[The Mighty Gryphon]

Jonathon, Have you ever pulled the radiator out and cleaned out the fins?  Doing that did more to lower the running temperature than almost anything else I did to the Moby Brick.

Is your replacement thermostat an OEM part?  The OEM thermostat has a shutoff for the radiator bypass that may not be on an "equivalent" thermostat.  If that bypass isn't being closed off when the engine gets warm and opens the thermostat a large portion of the circulating coolant will go around the radiator and not do any heat removal.   Even if you have an OEM thermostat, it's possible that it is not closing off the bypass.

Last, regarding oil consumption, try putting a quart of Marvel Mystery Oil in the crankcase when you do the next oil change and run on it for a couple thousand miles.  Moby Brick used a lot of oil before the MMO treatment by the guy who bought it from me.  He now reports that oil usage is down to less than a quart in 1500 miles.   

As far as valves, I would at least do the exhaust valves.  They are the ones most likely to burn when they get too tight.  Intake valves have the fresh charge cooling them. 

[Filmcamera]

Yes it is an OEM thermostat, it came from Max BMW.


The fins are in pretty great shape, I just checked them and though they are a few that are slightly bent overall it seems ok, I will try and post a photo soon. One of the funny things about CR is that there are NO bugs when you ride or drive.  I did 150 miles yesterday and did not have a single bug splatter, I have often wondered why, it is the same with cars, windscreens stay clean.  We never have salt on the roads and I try not to off road much so the fins tend to stay in pretty good condition. 


I will get a cleaner and try the reverse flush though, I am pretty sure the radiator has not had distilled water in it before I got the bike and the water here can be super hard.


Marvel Mystery Oil, ok let me jump on the right now, my missus happens to be in the US to celebrate Thanksgiving with her family so she might be able to bring some back because it is not available here for sure.

[Filmcamera]

Is this is the stuff?


Marvel Mystery Oil

[Martin]

If it hasn't been run on distilled water and the water is hard, it could be the problem. Built up scale can sometimes be hard to dislodge in both the block and the radiator. If it is severe you might have to flush a few times. And scale can also build up in the pump leading to restrictions. While the missus is in the US you might want get her to get you a few other things. A digital thermometer, a laser temperature gun all can be had cheap at Harbor Freight are invaluable and have multiple uses.
Regards Martin.
 

[Filmcamera]

Luckily I have both of those - well the digital thermometer is a digital meat thermometer but I guess it can do the job - I just have to use it without her indoors finding out...

[The Mighty Gryphon]

That's the stuff.

Even if the fins look good, there could be a lot of crap in between them.  I know I flushed out enough bugs from mine to feed a family of four for a week.  The only way I know to get them out is to soak the radiator in vinegar and run water from behind through the fins.  The only way to do it right is to take the radiator off the bike. 

Your bike has a lot of years and miles on it.  Don't assume the fins are clear. 

Cooling is a function of the coolant's specific heat.  Distilled water probably has the highest specific heat of any coolant you can easily get.  The trouble is, it has no corrosion preventives or anything to raise the boiling point.  I'm inclined to believe that BMW's recommended 60/40 mix is probably the best coolant mix for our bikes.

I suspect that "racing" coolant has additives to raise the boiling point so that it can safely run at higher than normal operating temperatures.  I also suspect that it's heat transfer ability at a given temperature may be lower than BMW's recommended mixture.  This may cause the engine to actually run hotter in order to achieve the required heat removal.  It's a case of the capability to run hotter causing it to run hotter.  Also, bear in mind that racing machines are running at high speed and have lots of airflow for cooling.

Remember that temperature equilibrium will occur at the temperature where the difference between the air temperature and the coolant temperature in the radiator allows the heat removal to equal the heat generated in the engine.  If you want to reduce the engine temperature you need to increase the heat transfer in the radiator.  Unless you go to a larger radiator, the only other thing you can do is increase airflow.  If you are running with a wide open thermostat and seeing high coolant temperatures, you need to look at radiator size and airflow.  It's all you have to work with.

[Filmcamera]

Ok that all makes perfect sense, thanks.


Let me get the radiator off and try a flush or two and also source a different coolant and go 60/40 disttilled water  v coolant.


Marvel Mystery Oil ordered...


She is gonna kill me, all the stuff I send means less clothes etc she can bring back... lol

[alabrew]

I just think that the cooling system is a bit small compared to modern systems. My '05 (and the '02) K12Lt don't run the fans like the '85 and '91 at the same air temps. 80F and humid, is that all =-} add 20 more degrees for here in the summer for months on end. I hear the fans kick on once I get home, but it is friggin' hot. Got stuck one Friday afternoon in stop and go traffic over 95F, damned hot. Tempted to split lanes to get the temps down, as much for me as the RS! If you are not seeing the temp light come on, I think it is working as designed.

[Martin]

I've never had trouble with overheating in the cooling system on my 75s even on the hottest days in traffic that QLD can come up with. Fuel system  overheating is another matter, currently  dealing with it. However my cooling system has only ever run with BMW coolant ( It is the same price if not cheaper than aftermarket coolants) and distilled water. And even then it has been flushed out a couple of times and the fin cleaned out.
I use a slightly different method to .75 I soak it overnight in hot water and dishwashing liquid then vacuum with my shop vac. You could still be running in the correct temperature range if the light is not coming on and it's not regurgitating coolant. Hence the need to check the accuracy of your temperature gauge. Laser temperature guns are now cheap as chips and have other uses. I also use mine to check that my cylinder temperatures are even.
Regards Martin.

[Laitch]

The coolant is Bel-Ray moto chill racing coolant.
I can check the valve clearances again but fixing them is a pain on the 16V bikes, if I have to do that I might do the whole thing and do the rings at the same time.

The Bel-Ray MotoChill instructions clearly state Do not dilute. By diluting it, you lessened its effectiveness. Incorrectly diluted coolant won't work well just because you want to save money. You've compromised cooling by doing that. All you need to use is long-life coolant—OAT-type—in the correct proportion with distilled water, or may Bel-Ray MotoChill as it was designed to be used. Long-life OAT-type coolant should be common, even in Costa Rica.

The whole thing that you're considering doing is a far reach from just adjusting valve clearances. If you knew that you'd avoid it like the plague. If you want to find out whether the rings are a problem, do a compression test. Give us the values. Follow classic compression test methods; brichbk explains the process in one of his posts. It was how he discovered one of his exhaust valves was near self-destruction and you can use it to determine if a rings in a cylinder might be faulty.

The distance between the top of the sight glass to the bottom represents approximately 0.6 liter. Be certain the crankcase ventilator assembly isn't clogged. A clogged crankcase ventilator can increase oil consumption.

Your moto should function well in the highlands of Costa Rica without a larger-capacity radiator but that's always an option if all other systems check out ok and overheating is proven to be a problem. Clean the cooling system thoroughly. Mix long-life OAT coolant with distilled water carefully in the recommended proportion. Measure the valve clearances carefully and use the correct size cam followers (buckets) to set them to their specified clearances. You want the intake valves correctly set too. It might get costly but those exhaust valves will only get tighter with more riding. If one of the valves break, then will be the time to contemplate the whole thing.

[Filmcamera]

I will do what I can, I have done a compression test in the past, if memory serves I got a fairly consistent 120 - 125 on each cylinder though 3 may have been down at 115 - certainly no zero readings like in the thread you mentioned.


I will search for the coolant you mention, believe  me it is not as easy as you think.  I might end up going to BMW and seeing if they will take my right arm for some OEM stuff.


I think you may be wrong about the top of the sight glass to the bottom being 0.6 liter.  I have had to fill it up many times and it has never been anywhere near as much as 20 fluid ounces to make up that. Granted normally I am filling from the bottom to the middle of the sight glass but that is generally 3-4 fluid ounces.


The valves I will check and look into again, last time I checked the general consensus of the forum was to leave them alone and ride, if they have got tighter that might change.

[Andy FitzGibbon]

A cylinder leak down test would also be helpful for evaluating valves and rings.

Andy

[Laitch]

I will search for the coolant you mention, believe  me it is not as easy as you think.
I think you may be wrong about the top of the sight glass to the bottom being 0.6 liter.
The valves I will check and look into again, last time I checked the general consensus of the forum was to leave them alone and ride, if they have got tighter that might change.

Anybody who advises that tight exhaust valves should be left alone is mistaken.
OAT coolant is used in most modern cars. It's the most common along with Hybrid Organic Acid Technology (HOAT) coolant. It's called Long life coolant.
As far as my being mistaken about the sight glass values, take it up with BMW. That value is published in both the K75 and K1100 BMW Rider's Manuals.

[Filmcamera]

I am looking into the procedure to change the buckets on the bike.  Clymers says I need two special BMW tools to get the camshafts out, they are $225! Add to that the buckets are $35 each, meaning I am looking at nearly $800 before tax and shipping to get them ehre.


Has anyone taken the camshaft out of a 16v engine without the special tools?

[alabrew]

Not the K100, but yes on the K1200. Basically, you zip tie the timing chain to the camshaft gears and then release the timing chain tension. Then remove the camshaft gears and the nuts holding the camshaft to the motor. The gears are keyed to the shaft with a pin to realign it on reassembly. Torque everything to spec. on reassembly. You should be able to find a youtube video of the procedure.

[The Mighty Gryphon]

I've had the head off my engine which involved removing the cams.  Reinstalling the cams is a kinda fiddly job, getting things lined up, but not really that hard.  I did it without the special tools and didn't have any problems.  As far as I can tell, the special tools just make it a quicker, no-brain kind of job.

[Filmcamera]

Great thanks to both of you.  That saves some cash at least