Modern Vespa

This is a first for me. My GTS300 sounded pretty dire for some time - very 'clattery', but ran just fine otherwise. I decided to check the valves first, and that made it slightly worse. Then I had to leave it alone for some months (other things took priority) and we had a spare scooter anyway.

Eventually, with some time on my hands I decided to take the engine out and check it all out. The first thing to do is to take the exhaust off - blow me if there wasn't some coolant inside! Not a huge amount, but a puzzle. Head gasket? That was my first thought. So with the engine on the bench I examined the old head gasket - it looked fine with no tears or signs of any problem. Having put a new oil control ring on (the old one looked ropey and fell apart very easily) I put new gaskets on and and checked everything else out that I could think of.

Fitted the engine back in, filled with oil and coolant, and she started on the second turn, sounding very nice after the oil pressure came up (about three seconds). However after a few more seconds, steam started rising from around the downpipe-exhaust joint, and there was some coming out of the back of the exhaust. Never mind, thinks I, there's always a bit of burn-off after a re-build.

BUT it just got worse, and on revving the engine, huge clouds of steam came out of the exhaust.

So, have I buggered up putting the new head gasket on (if so, why isn't exhaust getting into the coolant), or is there some other way coolant can get into the exhaust? An internal crack in the head?

Last edited by jimc on Tue Dec 10, 2019 1:05 pm; edited 1 time in total

Had just about the same thing occur to my 2013 GTS300 at around 15K miles.

Just above the exhaust outlet is a freeze plug (actually an access hole for machining, plugged by a steel freeze plug). Over a period of four years, it rotted out and was dripping coolant down onto the exhaust header pipe creating steam and coolant running down the pipe into the exhaust bushing area. Upon disassembly, coolant in the pipe.

Needless to say, within a few miles the temp gauge had gone up and I needed to shut down the engine to cool. Got home to find the coolant almost bone dry!

Here's the cause (found out the hard way). Coolant over time looses its ability to resist corrosion (in about 2-3 years). If an engine has any iron or steel internals that come into contact with it (like a steel plug in an aluminum head or a cast-in iron cylinder sleeve) you can expect corrosion.

The dealer plugged the area with JB Weld after I traded it for a new 2018 and used it himself for about a year until the water pump gave out (from the damage done from the old coolant) and then tore it down for a proper fix.

Bottom line, CHANGE COOLANT EVER 2-3 years!!!

That's my guess. New heads are cheaper than new GTS's.

Oo - that really got my hopes up - but a close examination shows that core plug in excellent condition and dry. Had a good look all around, the exterior is dry. Hrrmph.

Only by one order of magnitude. I see quotes around the $600 mark. I'm going to have to dream up some sort of test that'll give a more definite result. Pressure-testing the coolant perhaps? Hmm...

I'll add, the level in the reservoir doesn't appear to have gone down at all even though I've been producing loads of steam while peering up at the underside of the engine. I appreciate you don't need much water to produce loads of steam though.

It's as if the bike's protesting about vaping being curtailed!

I have a cunning plan - but it'll have to wait until tomorrow. It involves a bit of home-brewing kit...

If you want to completely disassemble the head, there's a process called magnafluxing to check for cracks.
Or this.
https://scooterpartsco.com/vespa/gts-300/gts-300-engine/malossi-cylinder-head-for-vespa-piaggio-aprilia?zenid=7c0067001fc0e9d6a84b5fcb5b0abb4c

I would pull the cylinder off, and check for issues with the base gasket, as well as those little O-rings, if they are in the 300.
I've had some head gasket failures, but usually mine involve exhaust pumping into the coolant system and dumping it out on my lap from the reservoir. You might use some copper gasket spray next time you install a head gasket. That seems to do the trick for me.
Is there a lot of little pitting on the surface of the head where it contacts the cylinder?

pressurizing water jacket when cold has always been accepted method for me for finding leaks.

Jim, this sadly is likely to be a cracked head as someone has already mentioned. I hope not but it's the logical explanation from what you have said. What about a Malossi head as a replacement? It'd be cheaper and you can keep your existing cylinder etc if you mod the piston, which isn't that hard to do, or spend the extra 400 bucks and get the whole kit and you'd have a flyer!

I'm coming around to that conclusion too. I'll do some more tests later, then see if I can find a cheaper way of sourcing a head, as we're saving for loads of trips next year!

That...sucks.
Here’s to finding the culprit and a fix.

A very kind person a few miles away has offered their old OEM head, after doing their own Malossi upgrade. When the rain stops I'll nip over there and pick it up. Then wait for new gaskets etc to arrive. Thanks Sam.

The engine will come out again today, and I'll strip the head down for a really good inspection.

At least this has given the scoot a thorough oil and coolant flush!

That's what the problem with my 2011. We tried changing the head gasket and the coolant still leaked into the engine oil. Lovely chocolate soup.

Like me, if you try the head gasket first and it still leaks. Call Scooter West and see if they pulled a head recently. The sold me one they were about to throw out for 50% off. I HOPE it's something else than a cracked head.

Good luck.

I forgot to mention this was the first issue when I had coolant in the oil. The original owner had taken it to a non-vespa certified shop. They put in the wrong coolant and this happened. Turns out that the wrong coolant also eroded the head and I had the cracked head about a year later.

So, it might not be a cracked head (yet) but that coolant plug. BUT it might lead to a cracked head as was in my case.

I can't see any obvious crack inside the exhaust port, and the core plug is pristine and intact. However the exhaust port, exhaust manifold and the entry into the silencer all look 'white' and washed with hot coolant. There is some sign of this on the valve heads themselves, but that must be some sort of blow-back at the end of the exhaust cycle.

In the picture showing the piston side of the head, looking at the upper right (exhaust) valve, at 3 O'clock position, it looks to me like a crack.

Goes and checks - no it's just an oil mark, easily polished away. Good thinking though!

could be a base gasket gone bad

Wouldn't the coolant get into the oil instead of the exhaust?

OK, well my next WAG is for the hole to be in the intake.

Nope. There might be coolant in the oil in that case (there isn't) but not coolant, real wet coolant, in the exhaust.

Could be.

Whatever, I will endeavour to get the replacement head tomorrow, give everything a good clean-up (again!) and wait for the gaskets to come from Jorge.

At least with our rainy weather here I've had something to do in the garage.

I think we have a winner. What looks like a slight casting flaw must have developed into a crack.

View into the intake port:

OK, I've collected the 'new' head from Sam - I owe you a service Sam! One gotcha is that my old head was a 2010 one, and Sam's is a 2011-onwards one. There's one subtle difference - in the dimensions of the tiny O-ring that acts as a gasket for the bleed screw passage under the thermostat housing. No biggie - but it'll mean a possible extra day waiting for that part as well as the rest of the gaskets.

Old part no (up to 2010) 297027 3.5x6x1.5 mm
New part no (2011 onwards) 878906 4x7.5x2.5 mm

Ha! That was a gotcha for me as well when I did the Malossi upgrade. The local shop (70 miles away) couldn’t locate the one o-ring they had in stock, and I, being rather impatient, manufactured the ring out of some EPDM I had leftover from a roofing project.

Glad you were able to source your issue.

Yeah, I thought of making one, or using a suitably sized grommet or something - but another day or two won't worry me with all this rainy weather we're having. Well done fixing yours.

Great photo of the crack in the intake port!

All the parts arrived and it's all back together; but although I've bled the coolant many times before, this time the bleed screw decided to weep. Hey-ho - fixed temporarily by tapping and fitting an M3 x 0.5 screw into it. New thermostat housing on order - to be changed out next coolant change, I can't be arsed to do any more for the moment.

Thanks again to Sam (samar67 of this parish) who gave me his old head. Sam, give me call next time your scoot is due for a service!

It's a bit rough your head cracking like that, but great to see that it all worked out in the end. Well done, Jim and Sam!

These reports on the forum are really useful, and help point us in the right direction if we have similar problems. Thanks for documenting it. I recently found someone else's report and photo useful to locate my problem when I had a coolant leak. (On the bike, that is.)

Cheers, Jim.

So it is thought to have been a fusion clique that has expanded over time?

I *think* I know what you mean. Yes, I think a small casting flaw - a small void perhaps - has gradually increased into a crack over time and many heat cycles. It's had ~40,000 miles of hard, hard riding, and it took several months for the symptoms to develop enough that an investigation should be the next step.

Thanks for sharing all this Jim. It has been interesting to follow the diagnosis and resolution. Congrats to you (and hero Sam)

Best
Miguel

Well done Jim. As ever, your knowledge and tenacity has won through and will prove very informative for the forum? Excellent!