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Discussion Starter · #1 ·
Some of you may remember my temp gauge failed and

not having a spare, I did some barnyard electronics based on rough testing

then knocked up an indicator which displayed the varying resistance of the sender

As an indicator it worked fairly well and the leds at 10-11 oclock would

tell me the bike was in the happy zone.



I though perhaps the leds at 2 to 5 o clock were a bit superfluous

well last night I found out they aint !



I wasnt far from home but held up in very heavy rush hour traffic and the leds started to rise

and when I got back the 4 o clock led was lit.



Examination showed the expansion bottle was full of coolant so the upside is

my home made gauge had done its job.

The downside is, even after replacing both head gaskets I'm still losing coolant

to the expansion bottle

Bollocks !



I'm hoping that its the 30 year old rad cap leaking and will try and source

a new one

If it still does it with a new rad cap then I'll have to start taking the

bloody thing apart again.

the bikes otherwise fine, it starts and runs well

theres no mixing of oil and coolant and it does take a while to fill the bottle

a 200 mile motorway ride to London and back raised the level but didnt fill it

its just the gradual loss I have to keep my eye on.



When it cools down I remove the rad cap and blow down the expansion bottle vent pipe

to push the coolant back into the rad

A week or few hundred miles later, I do it again.



Now I'm thinking if it isnt the rad cap then I either still have a leaky head gasket

or the pump isnt working



 

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Reg,you put a great deal of work into that illuminated tell tale.so,on that point ,,congradulations.


good luck on finding your leaky gremlin
 

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I would have hoped it would be something like a resistor failing in the LED ladder but I guess the full resevoir precludes that.





I posted this on marshalls thread re fans. showed a lot of crud in the cooling syst of this particular bike. A 78CX w 10k miles.



a couple pics of the thermostat housing showing the temp sender (from a junkyard bike) ... this was after I cleaned it a bit.




and a pic of the temp sender itself.
(yes it was a stuck mutha)





I hope it is something simple like a rad cap, stuck thermo, or something else relatively simple. Lot of crud to dislodge and restrict flow. pardon the xpost
 

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I think the same cap is used on some Honda cars, most auto parts stores should be able to match it up.
 

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Reg,am i correct in thinking...if it was a head gasket creating excess pressure to build up in the cooling system,then you would see air bubbles when looking down into the rad.
 

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Reg, I am thinking that your expansion bottle is just doing the proper thing. As the coolant heats and expands, it forces itself past the radiator cap and into the expansion bottle. When the engine cools, the reverse should happen. The coolant should be sucked back into the radiator.



Question is why is the bike heating up more than normal? Fan not comming on? Thermostat not opening? Clog in the system? I'll guess that it is the thermostat. Just try that one from picture 3 and see what happens. Or put yours in a pan on the stove and see if it opens just before boiling.



The Quick reference thread lists the auto equivalent for both the cap and the thermostat.
 

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I'm thinking the same thing; why is your bike running hotter than normal? There are numerous possibilities.



Two years ago I had an overheating situation that turned out to be a bad water pump impeller. Splines were completely gone. Found another one on ebay for $15.

 

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Discussion Starter · #9 ·
Thanks for the replies and suggestions

The thing is, it runs at normal temps until I lose the coolant

Then it overheats.

It isnt a quick process it may take a few hundred miles or week or two

of town use before the coolant fills the expansion bottle and the low level

of coolant increases the engine temp.

If I topped it up daily The gauge old or new, would read text book normal



I'm hoping a new rad cap will fix it
 

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It sounds like you are on the right track with a new cap, Reg. The old one isn't letting the coolant back into the radiator.
 

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Discussion Starter · #11 ·
Slightly puzzled now

Both of my old caps have 9 on them which I took for its lift pressure.

At a local car store I dismissed one cap that had 13 on it and brought home

one with 10 which looked like it would do.

then I realised the two locking lugs were too big and it was missing the big rubber

washer up underneath

Damn!

(the store was about to close and I was rushing a bit)

I checked the Haynes manual and it says the cap valve lift pressure is 12.8 psi

Huh?



Good job I didnt hack the one I just bought and kept the receipt.

I'll go back tomorrow and take my time rooting through all the boxes

on the shelf and get a 13 that fits.
 

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Slightly puzzled now

Both of my old caps have 9 on them which I took for its lift pressure.

At a local car store I dismissed one cap that had 13 on it and brought home

one with 10 which looked like it would do.

then I realised the two locking lugs were too big and it was missing the big rubber

washer up underneath

Damn!

(the store was about to close and I was rushing a bit)

I checked the Haynes manual and it says the cap valve lift pressure is 12.8 psi

Huh?



Good job I didnt hack the one I just bought and kept the receipt.

I'll go back tomorrow and take my time rooting through all the boxes

on the shelf and get a 13 that fits.


13 Ftlbs= 0.9 bar.



Check your water pump Reg.
 

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My thought is that the water pump is working, but there is a blockage somewhere. Your pressure is increasing to a level beyond that of the radiator cap - defective cap - realeasing fluid into reservoir - at normal pressure - OR - Normal cap releasing 'over pressure' into reservoir. One of these conditions is there. Also, check the return line from the reservoir - a pluged return line will limit the amount of fluid returning to the engine.



As Reg has indicated, the engine is operating normally until low fluid level - then temperature begins to rise. Thus the problem has to be somewhere in the lines back and forth from the reservoir.



Step one - determine if the cap is doing it's job - ie maintaining something substantial, but less than 0.9 bar

Step two - investigate both lines from the reservoire - a) to the radiator at the cap, and b:) the other one... LOL... can't for the life of me remember where it goes now!

Step Three - pull the thermostat and run the engine for a quick spin up to operating temperature without the thermostat. - this time of year, it shouldn't get hot enough, but the thermostat itself might be causing the cooling system to overpressurize - thus 'exhausting' fluid through the cap - as it's supposed to.



Hope you find the issue.
 

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Discussion Starter · #14 ·
WEel I got one from a 1977-198X Ford Escort 1.1/1/3 OHV

that fits well and is a 13 pounder so I'll see how I get on with that



I used the bike to go fetch the cap and now its topped up with coolant again the

temp gauge reads normal and get no more than the ten o clock led on.

If the new rad cap stops it dribbling out I'll be fixed,

Still dont know why I have two 9 pound caps when Hyenas manual and Rob Davis'

site info says the cap should be a 13 pounder.

I'll check theres no leaks preventing the coolant getting sucked back in when the motor cools too
 

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Shep's post above is correct and I've been caught on that on cars before, thermostats often have bar pressure ratings stamped on them instead of psi.

http://en.wikipedia.org/wiki/Bar_(unit)
 

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If the cap isn't sealing correctly it will "feed" to the expansion bottle at a lower than normal temp/pressure. By the same token it will not develop vacuum to draw the coolant back as the system cools again.Hope this is all it is - easy fix. Can't go wrong with replacing a possibly 30 year old cap anyway, they're cheap enough.
 

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Either you've got a head gasket leaking or a bad thermostat. In the first place, you shouldn't be blowing any coolant into the jug at this time of the year even in heavy stop and go traffic. You mentioned you have new head gaskets - well you wouldn't be the first person to have bad gaskets right out of the box. Have you checked and/or retorqued the head bolts?
 

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Discussion Starter · #18 ·
Yep fitting a new cap is the easiest cheapest and quickest first step

and it probably needed one anyway after all these years.

I may be grasping at straws and hoping for the best and

it may well be one of the gaskets hasnt sealed properly,we'll see.



I somehow doubt its the thermostat as when its topped up, the gauge/s

old and new will show normal running temps and its only as I lose coolant to the

flask that it starts to read hotter.



I'll give it s good run when the rain stops coming down sideways and see how it behaves
 

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Discussion Starter · #20 ·
Well I reckoned I might have been over optimistic about the rad cap and I was

Took it for a 40 mile ride today first 10 miles motorway at 70 ish

and the rest on A roads and town traffic.

The expansion bottle was low when I started and almost full when I got back

and the one o clock led was on too, it had been reading at normal most of the ride and only rose during the last 5 miles







The snag is, which head? the one I just did? the other one? both?

not sure a compression test will help as I doubt the cylinders would read the same

even if one wasnt leaking a bit.

I'm going to decant the almost full fuel tank and bung it in the beemer

and have a think about it before I throw spanners at it again



Bit of a pisser really the old things running pretty good otherwise

at least the beemers got heated grips, I was bloody freezing today

Edit:

Looks like I was wrong about the 200 miles/two weeeks bit too
 
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