Radiator Pressure

Am currently working on my project bike......a 2009 ST1300 P with 17, 000 miles on the clock.

The original radiator started leaking and after literally weeks of checking it turned out to be a problem on the upper neck pipe. One local radiator shop could not fix it so I opted to purchase a used unit from another funeral escort colleague who was parting out his 220,000 mile bike.

Cleaned everything out, replaced the thermostat just to be on the safe side, no leaks and both fans start without a problem. I did fill the radiator with a liquid flush and after a couple of runs I left the bike for 24 hours before checking the fluid level.

At this time I removed the radiator cap and was showered with radiator fluid. I have never seen this before, especially as the radiator and fluid were cold.....is this pressure normal or is there another underlying problem? Any advice / assistance is appreciated.

Regards
Barry

Definitely not normal to have that much pressure in a cold system. If everything were working properly, as the engine heats, the coolant would expand and enter the overflow tank. Then, when cooling, the coolant in the rad would contract and allow fluid to be drawn back into the rad from the overflow bottle. The rad cap is the "valve" controlling this. I would replace the rad cap, as it would seem to be holding more pressure than rated for. That could by why your rad split at the pipe seam.

Is there a blockage in the pipe to the expansion tank causing the pressure build.
I agree it's not normal.
Upt'North.

If the blockage was in the hose to the expansion tank, the weak point would have been in the fitting at the filler neck or the hose itself.

I suspect the cap. The opening pressure for that is 16-20 psi; and auto parts store that does tool loans might have a tester available.

If the cap failed and the system was being subjected to high enough pressure to split the radiator open, you'll want to inspect every inch of the system to make sure the hoses weren't damaged by swelling up.

--Mark

Bush said:

Definitely not normal to have that much pressure in a cold system.

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Could also be that the fresh refill left some air in the system (just like after my last car radiator flush at the dealer...!). An air bubble at the right place can expel coolant when opening the cap, without very much pressure being trapped.

Bush said:

If everything were working properly, as the engine heats, the coolant would expand and enter the overflow tank. Then, when cooling, the coolant in the rad would contract and allow fluid to be drawn back into the rad from the overflow bottle. The rad cap is the "valve" controlling this. I would replace the rad cap, as it would seem to be holding more pressure than rated for. That could by why your rad split at the pipe seam.

Click to expand...

Worthwhile verifying first if it is working just as described here. Let the bike idle until 3 bars and the fan kick in a few times and observe if the level is going up in the expansion reservoir and back down when the engine cools down.

Sometimes when there is air left in the system, a situation can occur where priming to the reservoir doesn't happen and the fluid expansion at temperature goes towards compressing the air pocket, with no flow to the reservoir.

I vote for a volume of compressed air trapped somewhere in the system due to an incomplete fill. Assuming you don't have another problem (kinked hose, blockage, etc.) refill the lost coolant and run it through a couple of heat / cool cycles. I've never needed to do more than that reassembling the cooling system. I put a little extra coolant in the catch tank to replace any expelled air and then check it over the next few rides until it stabilizes.

Bazza99 said:

Am currently working on my project bike......a 2009 ST1300 P with 17, 000 miles on the clock.

The original radiator started leaking and after literally weeks of checking it turned out to be a problem on the upper neck pipe. One local radiator shop could not fix it so I opted to purchase a used unit from another funeral escort colleague who was parting out his 220,000 mile bike.

Cleaned everything out, replaced the thermostat just to be on the safe side, no leaks and both fans start without a problem. I did fill the radiator with a liquid flush and after a couple of runs I left the bike for 24 hours before checking the fluid level.

At this time I removed the radiator cap and was showered with radiator fluid. I have never seen this before, especially as the radiator and fluid were cold.....is this pressure normal or is there another underlying problem? Any advice / assistance is appreciated.

Regards
Barry

Click to expand...

Do yourself a favor and checked or replace the radiator cap first. No need to blow out something while looking for the air in the system.

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The key question for me is where is the pressure coming from. A blown head gasket will not only let water into the combustion chamber, but exhaust gas can pressurize the cooling system. Obviously, checking/replacing the radiator cap would be the cheapest thing to do. I'm surprised that pressure that can split the radiator pipe did not pop the rubber cap off the overflow tank. Or fill this tank to the brim. Weakest link? If it happens again, you will need to look further.

SMSW said:

The key question for me is where is the pressure coming from. A blown head gasket will not only let water into the combustion chamber, but exhaust gas can pressurize the cooling system. Obviously, checking/replacing the radiator cap would be the cheapest thing to do. I'm surprised that pressure that can split the radiator pipe did not pop the rubber cap off the overflow tank. Or fill this tank to the brim. Weakest link? If it happens again, you will need to look further.

Click to expand...

Hi SMSW, hope all is well. I happen to know if blown head gasket is letting exhaust into coolant the rad cap if working will let pressure out to bottle, no split pipe. So back to first problem, replace cap, then test by pressurizing rad and or test for exhaust in rad.

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SMSW said:

The key question for me is where is the pressure coming from. A blown head gasket will not only let water into the combustion chamber, but exhaust gas can pressurize the cooling system. Obviously, checking/replacing the radiator cap would be the cheapest thing to do. I'm surprised that pressure that can split the radiator pipe did not pop the rubber cap off the overflow tank. Or fill this tank to the brim. Weakest link? If it happens again, you will need to look further.

Click to expand...

If it is the cap in this case, then it is holding back a level of pressure in the rad far exceeding its normal opening pressure, hence, no overfilling of the bottle. It would be the first time I've ever heard of a cap failing in this manner. Usually, they don't hold enough pressure when they fail.

Bush said:

If it is the cap in this case, then it is holding back a level of pressure in the rad far exceeding its normal opening pressure, hence, no overfilling of the bottle. It would be the first time I've ever heard of a cap failing in this manner. Usually, they don't hold enough pressure when they fail.

Click to expand...

When the rubber goes bad rad looses pressure out the cap. If the spring, plate, or shaft that parts move on get grime, rust, or pitted then valve won't open to release pressure inside the rad. I've seen both often.

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Dave.David said:

Hi SMSW, hope all is well. I happen to know if blown head gasket is letting exhaust into coolant the rad cap if working will let pressure out to bottle, no split pipe. So back to first problem, replace cap, then test by pressurizing rad and or test for exhaust in rad.

Sent from my SAMSUNG-SM-G935A using Tapatalk

Click to expand...

Thanks, Dave. Silly me - I didn't think about it before I wrote that and I confirmed what you are saying by checking my car radiator. The overflow pipe gets coolant from the radiator only when the cap's sealing washer lifts off its seat, so no flow to the plastic expansion tank from a sticking cap. Guess I was all wet on this one....(and not from anti-freeze).

Thanks to all for the advice/suggestions. I will go with the new radiator cap first and also check the various lines to make sure there is no blockage. I will revert as I move forward.

Ok, I am still having a problem. I have replaced the cap as suggested, reinstalled the original radiator, after having the neck joint re-welded $30. The replacement rad from my buddy sprung three leaks and could not be repaired.

After I filled overflow bottle to cold level I also re-filled the radiator with clean, fresh water. Started the engine and let it run until three were showing. The fans had not kicked in yet but the small radiator hose, located on the upper R/S of the rad, near the filler neck, blew off with pressure, even though it was secured correctly.

The only item that I have changed previously was the plastic three-way joint that connects two overflow pipes with a third and the thermostat. I did not use an OEM part on the three-way connector and am now wondering if this is causing the pressure problem? I have tried to identify the part in question but have been unable to locate it on the various sites (Bike Bandit, etc).

Any help is greatly appreciated.

I would look into doing a test to verify if any exhaust gas is present in the coolant system. Unless you're running pure water as coolant I can't think of anything else that would over pressurize the coolant system. Even then I don't know that it would run hot enough to boil the water to create that much over pressure.

Bazza99 said:

Ok, I have replaced the cap as suggested,

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Did you have a chance to have the old one tested? Would tell you right away if the prob is somewhere else.

reinstalled the original radiator, I also re-filled the radiator with clean, fresh water.

Click to expand...

Why not use the premix? What exactly to you have in the rad now?

the small radiator hose, located on the upper R/S of the rad, near the filler neck, blew off with pressure, even though it was secured correctly.

Click to expand...

Blew off the fitting (got disconnected) or blew apart? Any change in the level in the bottle?

reinstalled the original radiator,

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Verified you have free flow through it before reinstalling? On my car, I can leave the rad cap off and visually verify the coolant is circulating . Maybe can do the same here? I can also squeeze the hose and clearly feel the fluid circulating or not, maybe this is will also work with the ST?

Update.

The problem appears to have been in the T-piece hose connector behind the radiator ! I originally replaced the broken OEM part with a plastic ACE T-piece and this may have been too small.......creating the pressure. I replaced it with a larger metal piece, put everything back together, only to have one of the hoses split! Am now waiting for a Huntington Beach Honda metal T-piece and a complete set of rubber hoses and clamps.

Thanks for all of the previous input.

Bazza99 said:

Update.

The problem appears to have been in the T-piece hose connector behind the radiator ! I originally replaced the broken OEM part with a plastic ACE T-piece and this may have been too small.......creating the pressure.

Click to expand...

A restrictive fitting will not trap pressure once the engine is shut off (unless it is completely plugged).

There must be another explanation for the spraying you described in your first post, after the bike stood still for 24 hr.

Isn't there a technique for bleeding the cooling system somewhere - where you need to "blip" the throttle to make the system burp any air out ?

MidLife said:

A restrictive fitting will not trap pressure once the engine is shut off (unless it is completely plugged).

There must be another explanation for the spraying you described in your first post, after the bike stood still for 24 hr.

Click to expand...

He may have routed the lines incorrectly when replacing the 3 way tee. This could cause that issue.