Modern Vespa

I noticed the other day (had never checked before) that the right radiator warms up a lot long before the left even slightly warms up.

does the T-piece that splits the coolant coming from the engine have some thermostat sorta thing in it?

here's the part I'm curious about https://www.scooter-center.com/en/radiator-hose-connector-lower-t-piece-piaggio-vespa-gt-250-zapm45102-vespa-gts-250-zapm45100-zapm45101-vespa-gts-300-zapm45200-zapm45202-zapma3300-vespa-gts-hpe-300-zapma3600-zapmd310-vespa-gts-super-125-zapm45300-vespa-gts-supe-gp656449

Isn't that just because the right radiator doesn't have fan moving air, while the left one does?

Nope. In this story it's starting from cold and idling on the stand for several minutes and the fan had not come on.

Ah, I forgot about the fan not doing anything until REALLY needed .

For £18 rest assured there is no thermostat in that piece.

yet the upper t-piece is half the cost at £8 on the same website
https://www.scooter-center.com/en/radiator-hose-connector-upper-t-piece-piaggio-vespa-gt-250-zapm45102-vespa-gt-l-125-zapm31100-zapm31101-vespa-gt-l-200-zapm31200-vespa-gts-125-zapm31300-vespa-gts-250-zapm45100-zapm45101-vespa-gts-300-zapm45200-zapm45202-zapma3-gp577195


so has no one else checked this? simply idling from cold on the stand for a few minutes and checking with your fingers reaching in from the front?

it's totally normal. it heats up according to flow until thermostat fully opens and then everybody goes along for the ride.

there is only one thermostat in the system, it's in the head.

the bypass distributes the hot until the t-stat activates.

ok.

just surprised that Robot didn't mention it in his recent coolant flush video where he had let the scoot idle for "5 or 10mins" then he said the two radiators should be "evenly hot" (check 17:41 onwards)

You say several or a few minutes. Have you done the 5-10 minutes by a clock? If it's cold, probably add a little longer. Indoor service area like Robot's video would be ambient temperature.

Going from cold to warm is a lot more heat work than going from warm to hot.

ya missing my point. it's the unequalness of warming up that I am puzzled by which strongly suggests either a problem with my scoot or the t-piece directs an unequal flow to each radiator. I am not talking about when the bike is hot, just the warming up.

it warms up unequally because of the direction of the flow and the function of the thermostat.

I think you're looking to find a problem where there isn't one to be found.

again, this is totally normal.

Listen to Greasy.

Uneven would be one side hotter than the other AFTER it's warmed up. It has GET warm before it can equalize. If it doesn't equalize, THEN there's a problem.

maybe my use of the phrase "warms up" might have been poor. I mean warming up of the radiators not warming up of the engine

let's try this way ...

is there any flow to/from the front of the bike below 85C? my understanding is no.

above 85C my understanding is that water then flows forwards from the head along a single hose (under the left floorboard) to a tpiece at the front.

The tpiece directs to the tops of both radiators and the reservoir.

is this right?

Are the two outlets from the t piece that go to the radiators equal? That's my question


(diagrams are pages 250-252 in the gts300 workshop manual https://manuals.wotmeworry.org.uk/Vespa/GTS300%20Super/GTS300%20Super%20Workshop%20Manual.pdf )

1- your link is broken (it matters not to me, but perhaps somebody else reading along may be interested)

2- there is flow, the by pass provides flow before and even once the t-stat has fully opened.

now that we've established that there is flow and we have established that the radiators warm up at different rates what is the problem that you're trying to solve?

it's a thermostatic switch. it comes on when it needs to and then cycles and shuts off. just like all other modern automobiles. I don't see the problem here.

1. fixed. 2. flow to the front below 85C ok. didn't know that. my problem is my understanding, I get that - just trying to understand which bit of it is wrong.

so ... you kept mentioning direction, is the direction along the hose under my left foot and under my right foot consistent above and below 85C? ie is the flow under my left foot always forwards?

the direction of flow remains the same no matter the temp. the amount of flow varies depending on temp (t-stat open or closed)

I really want to answer what ever question it is that you're getting at, and I'm sure it's something fairly straight forward but it seems as though you want to approach this from a circular pattern, almost like you're gathering information before making an attempt at something.

never the less, I hope that answers what you were looking for.

thanks for this. I had thought I had asked the core of my question clearly enough but obviously not so this is why it's become drawn out.

so we have water flowing under my left foot going forwards to a tpiece at the front. this tpiece has 3 outs, one to the reservoir (which i guess we can ignore for now) and the other two go to the radiators. if these two outputs are equal then wouldn't the radiators warm up equally?

I'll give you a very scientific *maybe* but not necessarily. there's probably some heat exchange in the distance traveled.

moreover, I don't see why this would be an issue or present any type of a problem.

does the bike overheat? no? okay, then it's fine. leave it alone.

again. I'll ask. why? why does it matter at what rate the radiators warm up and if they warm equally? is there a specific reason? are you trying to accomplish something? are you trying to understand it because you think something is wrong and you want to repair it preventatively? is it because you want to modify the system in some way?

the distances travelled to the two radiators look similar enough so I wouldn't have though my fingers would notice such a difference it's not a problem.

I was briefly concerned when I noticed this after changing my coolant following Robot's video. I had never checked before. I have since then ridden over 2000km and all is fine. I just like to understand things and was surprised that Robot didn't mention this when he was saying to stick ya fingers in the front and feel the radiators.

On cold startup, the pump circulates coolant throughout the engine but not towards the radiators, because the thermostat keeps the coolant (mostly) captive in the engine. Nothing is actually flowing under your left foot until the engine temperature approaches the thermostat-designed temperature. As the engine coolant warms towards that level, the thermostat opens a small amount. This lets a bit of warm coolant push out, but pulls in some of the cold coolant, mixing in with the warmer stuff that is still mostly staying in the engine. The warm coolant dribbles through the slightly-open thermostat into the first radiator, then the second, at a rate that increases as the engine warms up, until the thermostat is wide open. The second radiator is going to stay cooler than the first, and the first will be cooler than the engine, until quite far into the engine's warmup.

he probably didn't mention it because it's just not something to be concerned with and as mechanics we understand what's going on and trying to explain a non-issue just muddies up the message that you're trying to convey.

it's an abstract, so to speak. why? because I said so, that's why.

exactly this.

it's like when somebody says: oh it's easy to change a water pump or flush the system. yeah, it is fairly straight forward and not terribly time consuming. testing it is where all the time goes!

I give up.

Either my English is bad or my fingers were lying to me.

I didn't mean for this to be the endpoint I just wanted to know why you thought it was of any relevance, that's all.

I can't tell you why it does that, just that it does. and that it does not have any bearing or effect in the operation of the machine. perhaps you could find your answer in the dark arts of fluid dynamics, I don't know that's above my pay grade.

but I can tell you that I do know why a dog licks its balls. so there's that consolation for ya.

The problem wasn't with the fan, the problem was with my memory .