bier9999

I heard two new rumors about Scion xD. Please help. Thanks.

1) Scion xD uses steel chain timing belt.

2) Before you turn off your Scion, if you hear the radiator fan on, you should not turn off the car or else you risk damaging the engine in the long run due to overheating. Instead wait for the fan to shut down before you shut down your xD.

notanoldfogyjustold

Your post got me to do a search for timing belt and it came up with this thread - https://www.scionlife.com/forums/vie...t=timing+chain

Now, one of the comments in this thread TOTALLY freaked me out:
"The motor in the XD is equiped with timing chain, no replacement interval as they rarley need to be replaced." (bold is MY emphasis)

WHAT????? I had a timing belt break on an '84 Honda years ago and it warped all the valves.

SeattleGuy

I like the cam timing/drive chain. I can live without the overpriced dealer replacement of belts every 70,000 miles or so. (Or the pain in the ___ of doing it myself.)

Though it may seem like a step backwards (all overhead cam motors used chains in times gone by) it really isn't. Most high performance modern motors still use them (e.g. Porche, BMW, Mercedes, Lexus, Cadillac, et al). It was and is not unusual for timing chains to last hundreds of thousands of miles since they are lubricated steel parts enclosed in the engine assembly. None of this is true for "belts."

Cam drive belts were introduced primarily as a cost cutting measure in small inexpensive engines. They also have the virtues of simpler design and quietness, but the trade-off is periodic, precautionary replacement. (On a cynical day I would say it also allowed dealers to make more maintenance money off otherwise low-profit cars.) Chains do not require periodic replacement. Interestingly, chain drives usually have lower frictional losses than belt drives and are much more efficient than gears. (Which is one reason why bicycles use chain drives.)

Another issue with belts was a disastrous "chain" of events if they failed in certain engines: If a cam timing belt broke the now unsynchronized valves would crash into the pistons and totally demolish the engine! Now that's freaky! It wasn't true of most engines, but there can be advantages to having valves that "intrude" on the combustion chambers when open: More power and/or efficiency can be wrung out of the motor. I don't know if it's true, but Toyota might have designed their new 4 cylinder motors with intrusive valve trains as both have the much more expensive timing chains and very good economy relative to their power.

notanoldfogyjustold

OK, that makes sense to a know-nothing. ;-) So, my old Honda had a timing belt, which broke & ruined the engine...........YUP, that's it! I'd agree that's a disastrous "chain" of events. But the xD has a timing chain, which is a good thing. Phewwww!

TX_WRX

timing chains breaking will cause a similar disastrous chain of events but it is not likely to happen. The timing belt is a steel reinforced rubber belt that lasts about 70k miles. So people neglected to change them or they prematurely failed and wreaked havok. A timing chain failure will have the same results, Valves out of sync with the pistons. But the timing chain is designed to go 100s of thousands of mile before failure. In other words it is not likely to happen. Also i owned an 86 MR2 and its timing belt broke and caused no valve damage, so it it possible.

bier9999

What about solving the rumor regarding the radiator?

"Before you turn off your Scion, if you hear the radiator fan on, you should not turn off the car or else you risk damaging the engine in the long run due to overheating."

I'm usually not anxious when it comes to radiators because my Camry has a dual fan radiator and usually doesn't turn on often. However, the Scion xD uses a single fan radiator and I hear it's like constantly on and I don't even use the air conditioning as often.

I'm worried because first, it's a new car and second, I have no idea when the xD will overheat until like the last 10 minutes when that red light comes on.

IMO, the digital temperature gauge on the xD stinks compared to other cars that uses meter style temperature gauge with a needle.

SeattleGuy

I've heard this rumor before. I tend to think it isn't true but can't be sure. The owner's manual doesn't mention it. Any damage done would likely be slow, cumulative and difficult to assess as distinct from normal wear. My fan doesn't run often. How bout you folks who live in hotter climates than the Pacific Northwest?

What I do know: Fans run when the temperature measured by a sensor placed in a cylinder head coolant galley reaches a certain threshold. Obviously the purpose is to push more air through the radiator. Fans are most likely to turn off at a standstill - such as waiting for a light after some hard driving - cause no air is flowing through the radiator. Is the engine in some sense overheating when the fan is on? No it's not. The engine is designed for such temperatures. Overheating is when the coolant flashes to steam, increases the system pressure and blows a gusher past the radiator cap. Pretty obvious! (Cars don't do this much anymore thank goodness. Back when they did more frequently (usually due to fouled radiators or worn out caps) obvious engine damage was not common except for some early production aluminum cylinder heads like the Chevy Vega. (Typical sequence: Hot but not overheating poorly designed motor -> warped cylinder head -> blown head gasket -> boil over -> tow truck -> big bills and/or new car.)

So does your coolant boil over when the fan's running and you shut the engine down? No it doesn't. Your engine is clearly not overheating the coolant. Sometimes temperatures in certain internal parts of the engine briefly rise upon shutdown because coolant and oil flows have ceased. It is a very transient phenomenon cause there is no more heat being created. Could the transient heat rise diminish the life of a motor? Possibly, I don't know. Could be an intrinsic weakness of internal combustion. In any case, it doesn't cause the coolant to overheat which would be telling. Would the increase be significantly more if the fan is running before shutdown. I don't think so. The thermal mass of the motor is constant and the coolant temperature is and remains below boilover - temperatures the motor is designed to operate at.

All in all I doubt it's worth the trouble, in fact the fan might even turn on as you sit there idling! Now turbocharger cool-down is another issue altogether!

btw I too would prefer temp, voltage, and oil pressure gauges. Will probably install a set sometime.

SeattleGuy

Should be "turn on at a standstill" Apologies...

xravexboix

The timing chain still has to be replaced, but it's beyond what they (Toyota) consider the service life of a vehicle. It should be checked around 150,000 miles to see if it has warped. There is a certain measurement for the distance between links on the chain. Once it's over a certain distance, the chain should be replaced.

As for the cool down fan, it's fine. The fan will run if the coolant temp is getting high and it isn't cooling down. This usually occurs in stop/go driving or any situation where air isn't being 'pushed' onto the radiator. It's fine to turn off the car once parked. I always give it 5 seconds or so once I completely stop, but it's just a habit.

Hondas (last one in our family was 00 Accord) had their radiator fan stay on for a few minutes after the vehicle is turned off... not sure why it was designed that way though =P

two.0XD

I'm in the process of switching to a nst pulley, but can't seem to find and toyota timing belt online to replace it. I know a lot of you guys just throw the old one on, but any time you remove the belt it should be replaced. I think thats pretty amazing that the belt should last 150,000 miles

Nateson

The belt for the nst crank pulley is the serpentine belt.

L337R3dN3k

To the original question on transmissions:
The 5-speed manual is shared with the Yaris. It's an old design, but has a reputation for being pretty much bullet proof. It is not a sport transmission, and it kinda shows -- but some people have found a short-shift kit improves it quite a bit. I left mine stock, as it's a daily driver and I don't care.

I suspect the 4-speed auto is also shared with the Yaris, but I don't know for certain.