[Rewhiteks]

Bought this bike used with only 4K miles on it. Ran it only 400 miles now it’s getting hit. Bike was supposedly serviced and touted as tip-top but found fluids a little low but all else seemed fine. Engine temp is creeping pst halfway and dans aren’t kicking on at all. Water pump is getting hot and coolant is pushing out of the reservoir. According to the book - nothing should be wrong, but I plan to remove thermostat, swap all fuses and replace the coolant. I’m hoping it’s nothing more than that. I’m afraid the water pump may be bad- just reluctant to break it open. Does anyone have any guidance for me? Thanks.

 

[AZ98Taxi]

From the Clymer manual:
Causes of overheating:
1.Low coolant level
2.Air in system.
3.Clogged radiator,hose or engine coolant passages.
4.Thermostat stuck closed.
5.Bad radiator cap
6.Open or short in system wiring harness.
7.Damaged water/oil pump.
8.Bad coolant temp sensor.
9.Fans inop.

It's not likely that both fans would be bad but you can make sure by undoing the connectors and energize with 12V. Then there's a relay that could be bad. It's in the electrical box under the fuel tank. Gotta take it all apart. The temp sensor sends a signal to the computer, so there's that,too.

 

[Rewhiteks]

From the Clymer manual:
Causes of overheating:
1.Low coolant level
2.Air in system.
3.Clogged radiator,hose or engine coolant passages.
4.Thermostat stuck closed.
5.Bad radiator cap
6.Open or short in system wiring harness.
7.Damaged water/oil pump.
8.Bad coolant temp sensor.
9.Fans inop.

It's not likely that both fans would be bad but you can make sure by undoing the connectors and energize with 12V. Then there's a relay that could be bad. It's in the electrical box under the fuel tank. Gotta take it all apart. The temp sensor sends a signal to the computer, so there's that,too.

 

[Rewhiteks]

Yep Ive read the Clymer Manuel, I guess I’ll just have to check it all. I was hoping for an easy fix being that it’s such low miles- I do t have a BMW store close so I will start with the hoses and thermostat then replace all the fuses and see where that takes me. I just can’t see the water pump being bad already. Maybe there’s a clogged hose. Idk. Thanks for your time and the advice.

 

[Beech]

Don't run without a thermostat. It is not a fix. If it is jammed install a new one. Work through the list, check to see if the radiator fins are clogged. Blown fan fuse cuts power to both fans. As you said, start with easy stuff. Remember that it is an air breather and below 55mph the temperature gauge starts going up. Even behind a truck you can see temperature change on the gauge.

 

[AZ98Taxi]

Is it overheating while you're moving? Or just when you slow down/stop?

 

[H96669]

Mine only overflowed when one of the plastic prongs holding the thermostat together broke.So start there.

Fans can,and will jam.One jammed and the fuse won't blow.You can try turning them with a stick through the outlet screen to see if jammed.

Dump the coolant and see if any black bits in it? The pump internals are powdercoated and a few like mine had peeling coating that could maybe plug the system.Pump itself is reliable, unless the impeller is corroded? If so I'd be worried about the other metal parts.

Radiators have rather narrow fins, and easy to damage.Perfect trap for sand, bug guts etc! They can't really be cleaned in place, most of us back then would remove the rads and clean them properly.

1/8" below the mid-mark is normal operating temp for them unless the cooling fins are blocked.

About halfway between the mid-mark and the red square (Overheat) mark is where the fans will start.

 

[Rewhiteks]

All of this is great advice. I did find a broken prong in the thermostat- guess I will get one ordered today. I noticed it getting warm when I was riding it- as I climbed through the gears hitting about 4500 RPM I noticed it getting warm but then it settles down to the halfway mark. I’m new to BMW so I was t sure if that was normal or not

 

[H96669]

A broken prong made my gauge act erratically.Progression from cold to normal wasn't even.Easy fix albeit expensive for what it is that thermostat.

 

[Rewhiteks]

A broken prong made my gauge act erratically.Progression from cold to normal wasn't even.Easy fix albeit expensive for what it is that thermostat.

 

[Rewhiteks]

Very expensive- like a $100 USD I was sure hoping to avoid that

 

[riderx]

My 2002 K12RS started overheating and pissing coolant out of the coolant overflow tank about 10 years ago,
MY solution came from these forums.
A new radiator cap (part # 17 11 7 675 523) (or "cover lid" as BMW calls it) solved my problem(s).
So far I've replaced my "cover lid" 4 times (about every 2 years).

As a side note, does BMW have a problem with weak or bad "cover lids" ?

The price on the first replacement was $28.72 (2012.06.14)
The last one was $43.26 (2021.06.22)

Change the oil.... and the "cover lid"

 

[Rewhiteks]

Great advice- I will do that. Thanks!

 

[H96669]

308,000 kms on my original rad cap.If I had more time I could show how to presurize the whole system via the bypass pipe with a regulated air supply and test both the cap release pressure and the system for leaks at the same time but I won't.

Cap is the same size as most imported cars so anyone with a cooling system/cap pressure tester could do that for you.21 psi.

 

[Rewhiteks]

Understood. Thank!