The Honda PCX / Forza / ADV150 / SH Forums

I have PCX 125 2012 that I bought 2nd hand. About 10 days after I got it, it overheated after a 30km ride. Took it to my regular mech (Mech1), he took it apart and discovered that the water hose joint was cracked (prev owner later told me that they'd discovered that too, but had had it repaired instead of replaced). We replaced the part, but the overheating has happened again once or twice - once on a short <3km ride, another time at the end of about 15kms.

Mech1 didn't have the capacity to do anything further, but was convinced that the prev overheating probs have caused some warping in the cylinder head and that I should have the head skimmed and the base and head gaskets replaced. The was so sure that he suggested I order the parts upfront, and then just take them to another mech to do the work.

I took the bike to Mech2 to ask about doing the job, but he's convinced it's not that. He did a quick check of the oil and radiator and says that since there are no signs of water in the oil, it simply cannot be.

Mech1's response to that had been that that would be a sign of a serious gasket issue, which he also didn't think it was. But he still thinks that that's the issue.

So! Out of interest.... what do y'all think??

I'm taking the bike to Mech2 tomorrow for him to check it out properly, but in the mean time I'd love to get some other opinions!

Thanks

(and if any are wondering, yes this is the same bike as my other post "Overheating and cutting out - from too much oil??" -- have established that there wasn't a oil prob, and would like to get some feedback now on the above, the question as it currently stands)

I gather these are general mechanics for scooters and bikes and not a dealer?

Hi, does it loose water does it boil with steam coming out the header tank, if the head gasket was leaking it could pressurise the cooling system with no sign of water in the oil also it could be a thermostat sticking. Lafree

Assuming the original overheat issue came from the defective coolant hose and the coolant leaked out hence causing the engine to overheat.This could result in a cracked head or warped head,or gasket failure depending how hot it really got.Actually need a few more specifics, like under what conditions does it still overheat..Short runs after 5 minutes, long runs etc etc. Without more details it will be hard to guess. Is the coolant capacity low after it overheats, you already determined that there is no coolant in the oil is this correct.As a quick check , put some dye in the coolant and run it and look for signs with a black light if you are low. More details ?

iceman wrote:I gather these are general mechanics for scooters and bikes and not a dealer?

Yep - general bike mechs. The Honda dealer wanted to charge me 15 hours of labour right off the bat just to take it apart to diagnose the problem, which already came to about 60% of what I paid for the bike! No thanks

Lafree wrote:Hi, does it loose water does it boil with steam coming out the header tank, if the head gasket was leaking it could pressurise the cooling system with no sign of water in the oil also it could be a thermostat sticking. Lafree

("header tank" = the plastic 'overflow' tank, right?) no, no sign of steam anywhere. doesn't seem to be losing much coolant (maybe a little, but defs not as much as it was before we replaced the hose joint). i've been keeping an eye on tank and radiator level (latter with less accuracy of course) as much as possible. there were one or two occasions (but not every time) that i opened the radiator and it seemed to 'pop' a little (pressure release?) and then immediately started filling from the overflow tank. had to quickly but lid back on it to prevent it from overflowing. is that not normal??

easyrider wrote:Assuming the original overheat issue came from the defective coolant hose and the coolant leaked out hence causing the engine to overheat.This could result in a cracked head or warped head,or gasket failure depending how hot it really got.Actually need a few more specifics, like under what conditions does it still overheat..Short runs after 5 minutes, long runs etc etc. Without more details it will be hard to guess. Is the coolant capacity low after it overheats, you already determined that there is no coolant in the oil is this correct.As a quick check , put some dye in the coolant and run it and look for signs with a black light if you are low. More details ?

overheated twice with me riding, one short ride, one long ride:
#1 - less than 3kms from home, and had actually stopped about a 1km in for about 3mins. was going up a fairly steep hill when it overheated. it was also a hot day with no wind. had been riding <60kms/hr all the time.
#2 - on a ride of about 15kms, also middle of the day, hot and no wind. had been on a freeway part of the time, riding at 80-100km/hr.

i've ridden it various other times, once even pushing to try to test it out to see if it was still overheating, but nothing. there was a bit more wind on that day though, so outside temp was cooler? but it's not overheating every time i ride.

coolant is mixed with water, so if there was leakage to the oil, there would have been signs re the oil going milky (right?). so it seems there's nothing getting into the oil.

I think your first 2 sentences are what Mech1 is suggesting happened. ...but is is possible for that to have happened, causing the bike to overheat sometimes now, but have NO water/coolant leakage into the engine (since there's no signs of water in the oil).

Check the coolant level it could be going out the exhaust. Any white smoke ??Any engine roughness misfiring? If all is good , no loss of coolant check the thermostat for a sticking condition.. Sometimes corrosion and or dirt can cause an erratic thermostat operation or you could have a partial restriction/obstruction. I would first look at the thermostat, bleed(purge) the system of any entrapped air..report back your findings. I would just replace the thermostat to eliminate and erratic operation

No smoke, no roughness or misfiring.
Before fixing the hose joint, I'd once lost engine power while riding on a freeway. But nothing like that now. She rides like a dream besides the temperature light going on!

Mech2 had also suggested that the prob might be with the thermostat. Will report back on further findings.

Thanks!!

Check the sensor.

Are there enough mechanics in the world....?

Good ones? Not just part switchers? Probably not.

You shouldn't be loosing any coolant. The expansion tank is there for a reason.
If you are pulling the rad cap off when things are hot your are going to defeat the purpose of the expansion tank and loose coolant.
Watch the expansion tank and if it constantly needs replenishing you have a problem.
As for mechanics they are conditioned to think the worse

This will be a long post so here we go.

1/ 1 way to check if your head gasket's blown. Let the engine rest, cold. Then open the radiator cap. If you see bubbles flowing up, you have a problem, likely with the head gasket. Otherwise, if you know how to take the seat off your scooter, you should look for the water pump, it will be installed to the cylinder head on the right side of the engine, with you looking at the front of the scooter. Check if the o ring that seals the water pump is leaking, it can be that one that leaks and causes problems.

2/ My guess is it's an o-ring somewhere that got bad and let air into the cooling system. After that everything gets worse and now you have a chance of warping the cylinder head. If the cylinder head is warped, you can scrape it off and be ok, change the head gasket and base cylinder gasket etc.

3/ My suggestion is to open up the engine. Hell the PCX engine is not that hard to open, I do it 4 or 5 times already. The annoying part is the plastic covers. Pulling the engine out and checking things should not be too hard for any mechanic. I'm not a mechanic, I went online and see maddiedog's guide and follow through with a service manual.

In conclusion, check the water pump o-ring. If it's not leaking, I highly suspect it's a blown head gasket. Blown head gasket does not necessarily mean white smoke or water in the oil. I have seen a case like this myself when the head gasket is only slightly damaged enough that combustion gas get though but not the reverse.

Do you still think this issue has nothing to do with oil overfills... be honest, just curious for the archives. Stuff happens to PCX but we like to know or at least have a reasonable guess if Honda's at fault or operator error.

Resurrecting this post. (For some reason I didn't get notified of those last replies, and so thought the thread had gone dead. Thank you to the PCX community that offered their input back then!)

So. The drama continues!
And has gotten much worse! Some of the questions you guys had asked (eg re the presence of white smoke/steam are now occurring).

Since I first posted, Mech2 has changed both the thermostat and the switch. He also put on a 1.1 bar radiator cap.
But I still get coolant pushing up into the reservoir, and the temp warning light going on, every single time I ride.
Mech2 also 'redirected' the overflow pipe at the top of the reservoir tank to hang down the left side so I can essentially now see as steam and coolant drips out. I have to top up constantly (currently using a cheap pre-mixed coolant since I'm basically just donating it to the road!). Liquid in the overflow tank is bubbling hot and steaming, every ride (even short ones).

Sometimes I feel like there's the slightest loss of power, but it may also just be because my hand slips a little on the throttle! There was only that once, right in the beginning, that I completely lost power.

Mech2 is now wanting to replace head and base gasket (which is what I'd wanted him to do in the first place, on Mech1's suggestion!).

My questions to the community:

1. What are your thoughts re the head and base gasket replacement? It's going to cost me about 20% of what I'd originally paid for the bike, and near double what I've already spent on trying to resolve this issue. If there's a good chance it'll fix the problem, then it's worth it based on the cost savings of the bike... but if not... :/

2. This "skimming" thing -- is that a specialised job, that not all mechanics would have the skills/tools for? Mech2 commented once that "these bikes hardly ever need that" (i think referring to smaller scooters, not sure he has other experience with PCXs) and I think he was kind of implying that he wouldn't do it. Going to another mech at this stage isn't really an option, because I'm pretty sure I'll get charged EVEN more for the job (because it's this repeated work with Mech2, I've managed to convince him to give me a discount on the head gasket replacement job).

3. One of the supposed 'quick fixes' Mech2 suggested was to buy a higher bar radiator cap. He'd tested a 0.9 vs the 1.1 and said that it pushed out less with the 1.1. Should I do that? Or will I just be creating a higher pressure system inside all these inner workings (that I really don't understand too well!) that may worsen the problem and cause whatever might be slightly-damaged to really just completely break? (eg if it is a damaged gasket situation - will increasing the pressure in the system with a higher bar radiator cap just possibly worsen that?)

4. Would using higher grade, and less diluted coolant make any worthwhile difference? (eg all this steam that's coming out now - is that the water in the coolant mix, and if i decrease the amount of water vs coolant, will it make it any better?)

BPT7594 wrote:This will be a long post so here we go.

1/ 1 way to check if your head gasket's blown. Let the engine rest, cold. Then open the radiator cap. If you see bubbles flowing up, you have a problem, likely with the head gasket. Otherwise, if you know how to take the seat off your scooter, you should look for the water pump, it will be installed to the cylinder head on the right side of the engine, with you looking at the front of the scooter. Check if the o ring that seals the water pump is leaking, it can be that one that leaks and causes problems.

2/ My guess is it's an o-ring somewhere that got bad and let air into the cooling system. After that everything gets worse and now you have a chance of warping the cylinder head. If the cylinder head is warped, you can scrape it off and be ok, change the head gasket and base cylinder gasket etc.

3/ My suggestion is to open up the engine. Hell the PCX engine is not that hard to open, I do it 4 or 5 times already. The annoying part is the plastic covers. Pulling the engine out and checking things should not be too hard for any mechanic. I'm not a mechanic, I went online and see maddiedog's guide and follow through with a service manual.

In conclusion, check the water pump o-ring. If it's not leaking, I highly suspect it's a blown head gasket. Blown head gasket does not necessarily mean white smoke or water in the oil. I have seen a case like this myself when the head gasket is only slightly damaged enough that combustion gas get though but not the reverse.

PS I tried what you suggested in #1 re checking for any bubbles. Bike is cold (not ridden since yesterday), overflow tank is empty (because of riding yesterday, and then I guess what had bubbled up flowing back as it cooled. that's what happens every time - i seem to loose that much coolant on each ride), radiator liquid level was visible on taking cap off. No bubbling noticed. I tried pinching the reachable pipes, still nothing. (Didn't start the bike though)

And has gotten much worse! Some of the questions you guys had asked (eg re the presence of white smoke/steam are now occurring).

Is this from the exhaust or the radiator / overflow ? If it's from the exhaust (after the exhaust is hot) you probably have a blown head gasket.

Another indication would be if the overflow tank has become discolored from oil residue or exhaust in the coolant.

On a typical engine, when the head gasket fails 3 things can happen but not all 3 always do. 1) compression / ignited fuel-air mix gets into the coolant system and overheats it / blows it out the overflow. 2) Coolant & oil get in the combustion chamber thus steam and smoke from the exhaust. 3) Coolant gets in your oil and seizes the engine.

If the gasket failed only, maybe it just needs replaced, but sometimes the head or cylinder mating faces need planed to true them as some defect or warp is what the actual cause of the failure was.

But I'm not sure if the coolant actually travels into the head or just the cylinder on a PCX ...... A "whisperers" experience is needed here ........

I'm looking at page 9-2 in the service manual at it looks like the coolant in a PCX does circulate thru the head as per a typical engine .... but again, I've never had a head off a my PCX so I can't vouch for sure.

springer1 wrote: Is this from the exhaust or the radiator / overflow ? If it's from the exhaust (after the exhaust is hot) you probably have a blown head gasket.

Another indication would be if the overflow tank has become discolored from oil residue or exhaust in the coolant.

Ah no - I think it's just coming from the overflow tank, not the exhaust. So ie it's the steam coming from the water that's boiling up into the overflow. The overflow pipe the mech moved is now hanging down on the same side as the exhaust though, and there have been one or two times that it's been really quite bad steam...makes me wonder if possibly those times it was coming from the exhaust...? (I'm about 70% sure it wasn't though)

There isn't any noticeable discolouration in overflow tank.

I'm looking at page 9-2 in the service manual at it looks like the coolant in a PCX does circulate thru the head as per a typical engine .... but again, I've never had a head off a my PCX so I can't vouch for sure.

What does that mean ito of the problem I'm experiencing?

Ah no - I think it's just coming from the overflow tank, not the exhaust. So ie it's the steam coming from the water that's boiling up into the overflow.

What does your oil look like? If compression or steam has been forced into it from a leaky head gasket it would usually have a milky/creamy color to it.

If the steam is from the coolant overflow, and your oil is the typical color, and your coolant is the typical color, and there is no steam/white exhaust system smoke then it sounds more like a coolant system 1) leak ....... or obstruction from either a 2) stuck thermostat or 3) air lock at a high point in the system or 4) hose crimp or 5) some foreign matter blockage in the system.

If you previously had any work done on the coolant system and the tech used silicone sealant, then that could also contribute the problem if if was't used very sparingly. Silicone sealant isn't a miracle cure, if too much is used on a gasket or not favored to the gasket or face's outer edge, it squeezes out internally and can form "worms" which are a potential blockage in either oil-ways or coolant paths depending on where it's used.

I've worked on engines, but not PCX engines, any ideas from more experienced PCX "whisperers" would supersede my suggestions. Wait until others contribute.

Stop buggering on. Pull the head.