Im trying to understand how a variable vane turbo works?

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Matata

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Absolutely nothing to do with marine....my diesel truck has a variable vane turbo. Some manufactures call it VNT . It is overboosting under certain driving conditions...I put a manifold pressure gauge on it....max boost should be about 16" hg but mine under heavy load goes up to 20/22 triggering the EML.....Anyone out there who can shed light on how to adjust? Regards Nik
 
Thanks Bruce...these turbos control the boost pressure by altering the vanes and hence don't have a waste gate but now i wish it did!!!
 
There’s an electronically controlled or vacuum controlled actuator that normally connects to a rod. The blades can get clogged up with soot and/or the actuator rod gets stiff. This means the variable vanes don’t react fast enough....or at all....often when coming off the throttle so you get an over boost. Dead common on lr discovery 3.

You can sometimes get away with spraying the external actuator rod and working it back and forth until it frees up. Had the same on a freelander....vanes where stuck but worked loose via the actuator rod and a good dose of right foot.
 
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I had a diesel X-Type Jag where the turbo failed. It went off to Midland Turbos for reconditioning and, during a conversation with one of their people, he said that he would never buy a vehicle with a turbo with vanes*, although it was quite a money maker for them.

I will probably never buy a vehicle with a turbo again, nor a JLR vehicle either. That car left a very sour taste.

* I have no idea what other types of turbos there are, and the conversation was 3 or 4 years ago, so I may have missed something.
 
DavidJ said:
I believe the D series Volvo Pentas have variable vane turbos. I guess they just have to follow the Volvo car engine manufacturers.
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Only the d3 has variable vane turbos, the rest of the series, d4, d6, etc use normal turbos
 
PCUK said:
When I was first making similar enquiries, Latestarter recommended giving the engine a a good hard blast every now and again to keep the vanes free.
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That is defo the solution once it’s free along with a good dose of Millers power eco max each fill up. A lot of disco 3/4 owners put a small amount of 2 stroke oil in the diesel for turbo and egr’s
 
Matata said:
Absolutely nothing to do with marine....my diesel truck has a variable vane turbo. Some manufactures call it VNT . It is overboosting under certain driving conditions...I put a manifold pressure gauge on it....max boost should be about 16" hg but mine under heavy load goes up to 20/22 triggering the EML.....Anyone out there who can shed light on how to adjust? Regards Nik
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It’s overboosting because the vanes are stuck.
 
volvopaul said:
A VNT turbo doesn’t have a wastegate , it doesn’t need one as it adjusts its boost pressure to the required throttle applied in relation to fuel and load .
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I already apologised. Dont need to queue up to beat me with a stick. Once is enough.
 
BruceK said:
I already apologised. Dont need to queue up to beat me with a stick. Once is enough.
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Poor Bruce :D.......we’ve not seen you get much stick from Marina Queen lately so I think it’s right and proper VP fills in until Roy makes an entrance :):):)
 
He's in hiding. Now that the rotten weather has arrived there's nothing to do but pillage his funbox so he keeps a low profile
 
The fault with variable vane turbos is due to long periods of slow speed running . The vanes aren't induced to move so they seize due to carbon build up.
Boats that are taken up to planing speed every trip may expect no issues.
Similarly in a car. If it is driven very gently all the time it may develop the same issue.
A regular good thrashing it what these things need.
 
Thanks for the interest guys...a bit of back ground..Its from a mitsubishi l200 turbo diesel...I have a boost gauge on it and can get around the overboost problem by watching the gauge and feathering the throttle. An actuator rod ( vacuum activated) moves a lever on the outside of the turbo. This lever sets the limits of the vane angles. The vanes direct the exhaust gases in radially towards the turbine at one position of the lever . At the other extreme of this lever position, the vanes are more in a tangential direction. By moving these vanes this is how it limits the turbo boost. The actuator rod works fine and the lever is very free ...any thoughts would be appreciated!!! Nik
 
Vacuum tube leak/blocked, dirty maf, air filter etc

Lots of info if you google l200 overboost. Probably better than a boat forum to be honest!
 
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