Higher gear, uphill, flooring it = hissing?

Flatulentoldgoat

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

peter3hg

It is probably just normal induction noise or turbo noise.
In a more appropriate gear it would be disguised by the sound of the engine at higher revs.

ontheroad1970

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

AdrianC

Lower revs, higher load, larger throttle openings, higher boost.

Yes, you'll hear induction noises you wouldn't driving more sensibly.

Goudy

It could be a leak between the turbo and inlet.

If one of the intercooler pipes has split or the intercooler has a small hole or the clips holding the pipes to it are loose or rusted through, it'll hiss or sound very flatulent depending on how big the hole is under boost as the boosted air is escaping.

It'll sound worse the more boost it's running and again, depending on how big a hole/how much boost it's loosing, it could be down on a bit/lot of power.

Diesels tend to throw out a lot of blowby oil into the air intake so the pipes/intercooler tend to have a bit of engine oil swilling around in there, so look for oily intercooler pipes or joints, if you find them there's sure to be a leak.

Some engines are pretty prone to split intercooler pipes, Some Ford Duratorqs were plagued by the pipe splitting FROM the intercooler to inlet manifold.
It always goes in the same place, just between the MAP and the EGR valve and it's always on the blindside, so unless you run your hand up the back of it, it's very hard to spot.

Also, check the crankcase breather that's plumbed into the air intake, that can hiss if it's split as it'll be drawing in air under high boost.

Oil can rot out these rubber pipes so it's often a worthwhile upgrade to replace them with silicone hoses. More often than not there will be aftermarket individual hoses and probably whole kits.

Flatulentoldgoat

ontheroad1970 said:

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

Speed > 50 = 5th gear. Do you drop down to second?

peter3hg

Flatulentoldgoat said:

ontheroad1970 said:

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

Speed > 50 = 5th gear. Do you drop down to second?

If you are "flooring it" to maintain 50mph then you are in the wrong gear. Speed should not be what determines gear selection, engine load should be.
Very simplistically you want to be in the gear where you need the smallest amount of throttle applied to maintain the speed. That may well be 3rd on a hill at 50mph.

ontheroad1970

Flatulentoldgoat said:

ontheroad1970 said:

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

Speed > 50 = 5th gear. Do you drop down to second?

Well if you are struggling in 5th at 50, to the extent that you're flooring it, then you're clearly in the incorrect gear.  You do know how to drive in the real world, don't you?  As you'd fail for inappropriate gear selection.

Grumpy_chap

Flatulentoldgoat said:

ontheroad1970 said:

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

Speed > 50 = 5th gear. Do you drop down to second?

Why do you only consider 5th gear and 2nd gear?

By definition, there must be two further gears in between those two mentioned.

photome

Sounds like to high a gear to me

BOWFER

peter3hg said:

Flatulentoldgoat said:

ontheroad1970 said:

Flatulentoldgoat said:

Friends van does this and I've always wondered what it was. I 'thought' it was a very slight vacuum leak but I can't find or see anything obvious. You only really hear it / pronounced when you're going up hill in say 4th/5th and flooring it. It's like a very mild, muted sound like a pressure cooker. Could a slightly slack/loose fan belt be a likely candidate. The only other thing I can think of is a Turbo going bad but it's been like this for ages and I think he'd have known if that was the case by now!!

Why would you go uphill  in 5th?  Or even in 4th?

Speed > 50 = 5th gear. Do you drop down to second?

If you are "flooring it" to maintain 50mph then you are in the wrong gear. Speed should not be what determines gear selection, engine load should be.
Very simplistically you want to be in the gear where you need the smallest amount of throttle applied to maintain the speed. That may well be 3rd on a hill at 50mph.

The 'highest gear possible at all times' mentality, popular with taxi drivers as the engine practically rattles itself off the mounts.