Water Valve Asm. -

General Bellett, Gemini 75-98, Piazza 81-93, Bellel, Florian, 117 Coupe, Minx, Aska technical discussion.
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Water Valve Asm. -

Post by impulsive » Tue Apr 24, 2012 7:19 am

Hi folks!

Its been a year and 5 months since I started the tear down of my 1987 Isuzu Impulse 2.0 Turbo RS. Yesterday I finished putting the last few bits together, and now it is time to solve a few final mysteries before I turn the key. One of the main things I found out when doing my rebuild, was that the PO had the "Water Valve Asm." deleted. The vacuum hose that went to the VSV was just plugged off and the coolant hose that goes from the radiator to the turbo coolant feed nipple was just joined with a coupler. This is the empty spot I am left with, you can also see the plugged off vacuum line:

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So, my question is, what does this part do and is it really needed? Obviously, my car was running ok before the tear down, so I know it can run without this part, but I still want to know what it does. I assume it just regulates the flow of coolant to the turbo.

It is Isuzu Part # 8941749341.

Here is a pic of the "completed" engine bay. :)
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Thanks - Bart
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Post by eyecon » Tue Apr 24, 2012 9:57 am

Hi Bart, I've been following your progress on the 'zone' and it's coming up really nicely. Great job. Re the deleted part, my logical assumption (and mind you I'm no expert. There are others on this forum far more knowledgeable than me) is that it was supposed to bring the turbo to operating temperature sooner on a cold startup, then the valve would open allowing normal flow of water from the radiator at operating temperature. I believe something similar was discussed elsewhere on here and I'll see if I can find it.

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Post by eyecon » Tue Apr 24, 2012 10:45 am

Does this help? I believe this part often gets removed because they either break or perish, or due to reliability concerns.
http://www.isuzupiazza.com/forum/viewtopic.php?t=436

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Post by impulsive » Wed Apr 25, 2012 2:21 am

Thanks, eyecon.

Very interesting infomation, as last night, I got a completely different description from the Isuzu Guru, Jerry Lemond. He said this:

"THE WATER VALVE IS IN THERE TO KEEP THE WATER MOVING ON A HOT ENGINE SHUT DOWN, IT WORKS ON A HEAT/SIPHONING EFFECT TO HELP COOL THE TURBO ON A HOT SHUT DOWN, AS LONG AS WATER CAN CIRCULATE THRU THE LINES THE VLV ISNT REALLY NEEDED , IT MOST LIKELY STARTED LEAKING SOMETIME YEARS A GO AND SOMEONE JUST REMOVED IT"

So I did some more reading, and apparently what this water valve is supposed to do, is help prevent what is known as "turbo heat soak". Basically, when you shut down after a good run and everything is still nice and hot, the turbo gets super heated more-or-less and causes coking of the oil and burning of the coolant that is just sitting in the lines. So, this water valve uses a heat siphoning method to keep water flowing after shutoff, which, in theory, should help reduce heat soak.

This all makes perfect sense to me, especially now having the big picture. If you have been following my rebuild on the Zone, than you might remember these three pics:

This is the oil tube from the turbo.
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What is all that black stuff? You guessed it, coked oil. :confused1:
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Then you have this nipple, this is the coolant return nipple off the turbo. This nipple was so corroded and clogged, I couldn't even get a pick through it. CLOGGED ROCK SOLID.
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So, my goal is to get a water valve, either OEM or aftermarket, back in place to help prevent this from happening again. The other option is to sit in my car and let it idle for 5-10 minutes to cool down after I drive it. That option is fine for leisure driving, but not for when I am already 10 minutes late for work. :rolleyes:

I think I need to talk to some performance shops that deal with turbos and what not and see if we can come up with something. The one thing I still don't quite understand, is what does the vacuum line to the VSV do? I'm guessing it shuts the valve on and off or something. Maybe when the motor is running there is vacuum and it shuts off the valve so the turbo gets hot and boosts more and then without vacuum is starts the coolant flow, but then that kinda doesn't make sense either, because you want coolant flow all the time I would think.

Thanks - Bart
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Post by eyecon » Wed Apr 25, 2012 7:55 am

This siphoning method after shutdown is intriguing since the valve sits higher than the turbo, unless of course the coolant is allowed to flow back the other way via the open valve on shutdown. Yes I can see the genius and value behind the purpose of this valve. Perhaps an understated turbo preserving component judging from those pics. But it's always a good idea to let the engine idle after a good or hard run for between 1 to 3 minutes anyway, because the oil is still sitting there under the turbo. Idling the car between 5 and 10 minutes would be an overkill unless you've absolutely thrashed the heck out of it on your way to work. But I suspect you're not that kind of driver. Well done Bart. If you need help find this part let me know.

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Post by IZU069 » Wed Apr 25, 2012 10:19 am

Cooling after shutdown isn't that important.
It's like engine coolant - It does not matter if it heats up (unless it boils) because the source of the heat is cooling down; the headgasket & surrounds & pistons cannot get any hotter.

Though older turbos needed a cool-down after a thrash, they did not have water cooling.


As to the Piazza turbo coolant valve, how does it stay open after the IGN is turned off?
(Though I have forgotten my own writings - is it normally open and closed when cold? I suppose a quick link and read...)

And not that I have looked at that side of the electrics, but I do not recall it being part of the same circuit as the dizzy/ignition-module run on fan. (But if it's normally open, that's not an issue. But the valve IS NOT there for that purpose. If it was, it would simply be omitted.)


That last pic above of the block's water outlet is simply corrosion, probably accelerated by incorrect coolant.
That can mean other corrosion elsewhere in the system that has tended to block smaller feeds.
That turbo gunk may simply be the sludge that has hung around and been burnt.
The same goes for the oil supply - insufficient oil & filter changes, oil too thick etc.
It's not a problem I am aware of in the Piazza's turbo.
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Post by impulsive » Thu Apr 26, 2012 7:02 am

Thanks for the info guys. Makes me feel better about not having this part in there.

Now, here's another question. The power steering pump reservoir clearly says "power steering fluid only" while the manual clearly says "use only Dextron II" in the power steering. So which is it? The bloke at Napa Auto Parts here said it doesn't really matter, you can use either, but I didn't like that answer...

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Post by Bugle » Thu Apr 26, 2012 10:18 pm

"Power steering fluid" isn't all that specific. DEXRON II is a specific standard for auto/PS fluid so if they specify that then go with it, or DEXRON III which is supposed to be backward compatible.

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Post by wedgenut » Fri Apr 27, 2012 5:56 pm

The JDM models (up to 1986 at least) didn't have water cooled turbos and yes coking is a problem but a $30 turbo timer sorts out that issue very easily. I usually have mine set at 1 minute for normal use and step up to 3 mins if been thrashed. Last time I had it off to replace the bushes and rings it was clean as a whistle, mind you I change my oil and filter every 3000km's.

I just wonder what value messing around with the water valve would actually be?
So many cars, so little cash

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Post by IZU069 » Sat Apr 28, 2012 1:20 am

AFAIK, it only shuts off for the cold coolant.
Otherwise it's normally open.
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