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Boiling over but not overheating?

Old 09-13-2006, 08:50 AM
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Question Boiling over but not overheating?

I've got a 98 SH with 25,xxxx miles on it. Always been a damn good bike.

Recently, a "boiling sound/steam" started eminating from the coolant overflow container. The temp gauge (idiot gauge that it is) always read halfway or slighly above/below (1 needle width either side of halfway), but it still boils.

I thought at first it was bad coolant, so I did a flush/re-fill, making sure to burp all the hoses/get all the air out of the radiators. Same problem.

I checked the compression. 180PSI both front and back cold, 190 PSI hot. Holds pressure in the cylinder with no problem, but didn't to a full leakdown test.

Someone suggested theromostat, but @ $35.99 from my local dealer, it's rather expensive to just start replacing parts on a guess. Since the temp sender for the gauge is on the thermostat housing, I'm figuring if it was the thermostat, I would see the "hot" condition via the temp gauge. Since the Temp gauge reads normal, it's not the thermostat...I'm wondering about my water pump?

Anyone else have any ideas?
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Old 09-13-2006, 12:23 PM
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water pump problems seem very uncommon on these bikes, I have only seen 1 posting in the year I have been here. You can test a thermostat with hot water and a high temp thermometer on your stove if you really want to prove its good or not. They normally start to open at approx 170 degrees. As for testing the water pump when its running and the thermostat opens you should see the radiator level drop at the cap and see the coolant circulate.
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Old 09-13-2006, 12:31 PM
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If it's not overheating but coolant is passing into the overflow tank check the radiator cap seal and if ok check the pop off pressure for the cap.
It should be 1.1 to 1.4kgf/cm aka as 16-20psi, at least that's what my manual tells me.
Based on your description I'd be willing to bet a dollar to a donut that it is the cap.

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Old 09-13-2006, 02:18 PM
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I agree, check the cap out and make sure the rubber seals aren't all rotten. It might not be on all the way, either. I thought I had one tightened down all the way on another bike, turned out to have one more 1/4 turn to go before it was tight. It was doing the same thing you're talking about. If you don't have adequate pressure in the system, the boiling point of the coolant will be lower and produce your symptoms.
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Old 09-13-2006, 02:21 PM
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I've seated the cap several times with the flush-refill of coolant/water, so I know it's on tight, but it might be a bad cap. I'll see if I can devise a way to test it out tonight.
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Old 09-13-2006, 09:06 PM
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Unless you have a cooling system pressure tester you'll probably have to take the cap to a radiator shop and ask them to test it. If they are nice they'll do it for free.
If you have a good relationship with your local dealer they might do the same but I've learned not to hold my breath.
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Old 09-14-2006, 01:09 PM
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The cap is the problem! you need it to maintain presssure or it will let the coolant boil. It's a cheap part, replace it.
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Old 09-14-2006, 03:55 PM
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Before replacing the cap, try bending the 2 locking tabs a little bit, making the cap sit tighter on the radiator (decrease the overall height). This may be all that is needed. I had a mechanic tell me once that he did this on my old Magna, after some minor engine work was done.

Since the temp gauge sending unit is mounted on the thermostat housing, and not directly on the engine itself, a lack of hot water circulating through the thermostat will make the gauge read cold, when in fact the engine itself may be very hot. I've had this experience with other honda bikes in the past - very low water level = cold temp gauge.
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Old 09-05-2008, 01:12 PM
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Ressurecting an old thread...I'm experiencing the same problem after switching to straight water for the track. My coolant(water) boils in the expansion tank, which would be normal since the tank itself is not under pressure like the rest of the system. Would Waterwetter heal this problem? Last night after hitting every stop light, I stopped and she was tinkling coolant out and boiling. I haven't checked the cap yet, but after taking a crash course in radiators in the last week, the cause could also be the thermostat not allowing adequate circulation. Temp guage is staying within normal range, but its still boiling. So Waterwetter? Or switch back to regular coolant?
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Old 09-05-2008, 07:30 PM
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Originally Posted by Lefin102 View Post
The cap is the problem! you need it to maintain presssure or it will let the coolant boil. It's a cheap part, replace it.
+1 Buy a new cap.
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Old 09-06-2008, 05:15 AM
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Boiling over but not overheating <- that sir is a oxymoron.... its over heating just not outside the engine where the temp sensor is ... only read right if theres flow
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Old 09-06-2008, 05:17 AM
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Originally Posted by Hotbrakes View Post
Ressurecting an old thread...I'm experiencing the same problem after switching to straight water for the track. My coolant(water) boils in the expansion tank, which would be normal since the tank itself is not under pressure like the rest of the system. Would Waterwetter heal this problem? Last night after hitting every stop light, I stopped and she was tinkling coolant out and boiling. I haven't checked the cap yet, but after taking a crash course in radiators in the last week, the cause could also be the thermostat not allowing adequate circulation. Temp guage is staying within normal range, but its still boiling. So Waterwetter? Or switch back to regular coolant?
water boils at 100 C 212 F at atmosphere....once again the temp gauge wont read steam either.... very misleading only senses water i wish they would not have put it on the back side of the t-stat housing in the rear head water jacket would be way better in my optnion

.....Straps on adult diaper and flame suit....
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Old 10-05-2008, 11:37 AM
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Well after comparing the Superhawk cap with the RC51's, the rubber on the Superhawks appears to be expanded, causing it to jam in the hole and without sealing properly. So the water goes straight to the expansion chamber and boils since there is no pressure. I put the RC51 cap on and got it up to operating temp with the fan on, NO BOILING WATER! Wooho!

But then I F***ED up royally and took the cap off a little too soon.
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I drove myself to the hospital with 3rd degree burns around my eye. That hurt! No damage to the eye or my sight cause I squeezed them shut when the geyser began. But I missed 2 days of good riding and will probably not get back to work until Friday.
But hey, the problem is fixed once the new cap arrives later this week. Lesson learned even though I already knew what would happen.
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Old 10-06-2008, 01:54 PM
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Holy Crap man! Glad your sight is okay. You won't forget that lesson for sure.
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Old 10-06-2008, 03:41 PM
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Well... It might sound cliche, but there is no substitute for firsthand knowledge... Knowing it was a bad idea didn't stop you, the memory of the burns will... don't ask me how I know...

Glad you are going to be OK, getting it in the eye would not have been fun...
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Old 10-06-2008, 05:19 PM
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Yes and if it ever necessary to remove a radiator cap while the engine is warm do so veeerrry slowly and use a rag . Dude you are so lucky you didn't loose that eye man I almost had to change my skivvies after seeing that.
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Old 10-06-2008, 07:55 PM
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I used a freakin rag too! That way I didn't burn my hand when I touched the cap to take it off. It was late, I was trying to get stuff done, and I brain farted at the WRONG time! Yesterday I added some WaterWetter to the RC and went to check the level after it ran for a few minutes, but it was an hour later and I was like a little girl touching a spider. (or me touching a spider) Wish there was a trustworthy shop around so I could pay to get this radiator garbage done for me.
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Old 10-09-2008, 10:39 AM
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Originally Posted by filter69 View Post
Boiling over but not overheating <- that sir is a oxymoron.... its over heating just not outside the engine where the temp sensor is ... only read right if theres flow
Not exactly. Water has a much lower BP than antifreeze/coolant. Racers (at least cage racers) use additives approved by racing organizations to keep the BP up.

Here is one from royal purple.
http://www.scoobytuner.com/products/...&productID=878
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Old 10-09-2008, 03:30 PM
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An easy way to check the cap hot or cold is to squeeze a hose and look at the over flow bottle. If you can make air bubbles in the bottle then you know the cap is not sealing.

Glad your ok learned this on a long time ago the hard way to. Burnt arm pit from it shooting up my jacket sleeve.
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