Cold house - inefficient heating?

[Bruce]

If the judder is at exactly the same RPM in all gears, it will almost certainly be either the engine mountings or the exhaust system.

[Bill]

In message , Bruce writes

And I wish I could have found a conventional diesel automatic at a price I could afford and that was new enough to satisfy SWMBO.

I've had conventional automatics for ages and have had no transmission problems ever. My Disco diesel automatic is fine even with quite a bit of low-range towing of heavy boats around a field, and son's '97 Merc diesel auto that I found for him locally is excellent. In the real world, the small consumption hit is negligible compared with the advantages.

[Bill]

In message , Bruce writes

I don't think it's the exhaust system. Too violent for that.

It's only when the engine is under load, most noticeable when accelerating hard at 40ish mph in top. Less noticeable in the lower gears.

Also when reversing out of my path - full lock, uphill, slowly because of obstructed vision - the clutch feels very "gritty". I have to keep the revs there at just over 1100 and upwards to avoid stalling, and it just doesn't feel right. I used to back the old Defender 200tdi out and it just worked without me noticing anything odd about the transmission (although I did have to get rid eventually because my clutch knee played up).

[js.b1]

Apologies, I did not mean to imply a pure straight cut :-)

Gearboxes have an obvious helical cut.

- High-torque low-revving turbo diesels impose high loads on gearbox teeth

- Gear teeth profile & mesh is more "straight cut" that it would normally be

- Gear teeth are higher strength & lighter weight than they would normally be

The problem is that profile & mesh permits higher backlash (slop) under no-load conditions, such that the natural RPM variation of the engine results in a rattling as backlash varies from zero to maximum. Backlash is where two gear teeth despite being meshed together can still move within that mesh by a small rotational distance.

A DMF has dual masses linked by a viscoelastic fluid which acts to eliminate this RPM oscillation which would otherwise create a rattle that "hunted" (comes and goes with varying amplitude). Indeed I think the ECU might actually pick up on the oscillation and whilst trying to control it due to lag in the feedback loop actually create positive reinforcement (make the rattle worse).

Camshafts (gear driven DOHC) have an obvious helical cut.

- However during idle the normal RPM variation will cause the intake v exhaust camshaft to vary slightly in RPM resulting in a varying backlash against the gearteeth (from zero to maximum backlash).

- The net result would be a rattle, basically you want the gear teeth to have zero backlash but can't actually achieve that in practice - so instead "slow" one shaft slightly so as to achieve an effective zero backlash condition.

- Some vehicles achieve this "slowing" on one camshaft by a second set of straight gear teeth which have an odd number of teeth - so breaking up this hunting rattle effect. Others use a friction spring, or a combination of several methods.

Hope my explanation is clearer. Easy with a simple animation showing two gearteeth turning - first showing what backlash is (forward-back clack) and then second showing how backlash varying results in a rattle that "hunts" as it drifts repeatedly between zero & maximum over time.

I think DMF are solving a problem that is acoustically minor, perhaps invented or over emphasised by marketing or focus group testing. They are expensive - but then so is much of a turbo diesel. That is before one considers epoxy encapsulated ECU and I should add numerous short trips on some turbo diesel result in coking of the oil reducing oil passage size - eventually starving first turbo then (rod) big end bearings with catastrophic repair cost.

[Bruce]

Thanks for that. In that case, my bet's on the engine mountings.

[The Natural Philosopher]

you mean you could here it over the doors and windows rattling?

[The Natural Philosopher]

Thts how its written on my cover..

yup. Until such time as as the competent lose their liberal soft hearts and discover that survival of ALL consists of them taking over the reins.

[The Natural Philosopher]

yeah. We splashed out on an auto freelander. Lovely car, cheap and economical it aint though.

[Edgar Iredale]

The camshaft is chain drive on Series 1 Land Rovers. On the petrol engine the inlet valves are overhead while exhaust ones are at the side. Edgar

[Bob Eager]

You're quite right...I'd forgotten that!

I do remember being outside on a very cold day, grinding the exhaust valve seats!

[Jules]

Lots of old Fords seem to have the kind of setup you mentioned, though - "low slung" crank with direct gear drive, then pushrods to the top. Whether they were ever straight-cut though, I don't know (they're helical on my 1967 Ford truck, but maybe they were straight on earlier Fords)

Even the 3-speed 'box on the truck has synchro, at least on second and third (there's a bit of a knack to getting into first, but that might just be slop in the column-shift mechanism; it's on the to-do list to investigate sometime)

Brr. My last Landy experience was a few years ago: breaking down in the middle of nowhere, middle of winter, and middle of the night when a core plug let go in the basket-case V8 LWB that a friend had bought. The heater didn't work anyway and the doors didn't exactly seal well, so it was no colder outside than in. ISTR neither of us had a working phone, but we managed to spot a rural house that still showed signs of life, and borrowed their landline to call the AA.

Talking of cold, it was -37 here (without windchill) this morning - I went out to check the fluid levels in the car, and the oil was frozen to the dipstick. Time to invest in a sump heater, I think...

cheers

Jules

[js.b1]

Or synthetic oil pronto unless you want a spun rod bearing :-)

[Jules]

Hmm, wonder if it'll take synthetic? I thought there was something about it only being suitable for certain engines* (or maybe it's just that you can't mix it with non-synthetic oil and so need a totally dry engine before you can put synthetic in). I shall have to go a-googling...

• the car's a '97 Toyota with their 3-litre V6

cheers

Jules

[Huge]

[Steve Firth]

Hmm, thats between the boiling points of hydrogen and helium, close to the boiling point of neon.

Or do you mean in degrees F/C (just about the same thing -37/-38) in which case it's cold but at least didn't mean that quantum effects were starting to disrupt the process of eating breakfast by moving the cornflakes from the packet halfway across the room.

[Fredxx]

What? Hydrogen is liquid below -253 degs C!! Even Neon has a boiling point of -249 degs C.

Which temperature scale are you thinking of?

[PeterC]

The negative side of 0K?

[js.b1]

For obvious reasons additive packages are compatible, and you should stick to the correct weight of oil for your temperature. Whilst many people like 0wXX synthetic oil for winter, I think it's a bit too thin (the first figure is cold viscosity) and 5wXX is better. Synthetic allows better cold & hot weather protection without the oil sludging, quite a few oil FAQs out there.

Synthetic does have a stronger detergent package and more anti-wear additives than conventional oil, but if all that is plugging a leak is sludge you will soon have other things to worry about.

You may see slightly higher oil consumption on lift-off at high RPM (pull thro under vacuum from the valve stem seals, piston rings). That can easily be monitored. Other oil leaks need fixing just as with any car - usually oil pressure sender.

Sounds like the infamous Camry, reliable & popular USA/Canada-side.

Beware semi-synthetic does not need to have much synthetic to be called synthetic. The pour point of many cheap oils is not that good vs -37oC temperatures. Starvation is never good for bearings and V6s often have marginal oil path by #6.

[Jules]

Yeah, that was C - I was kind and did the conversion from F for people :-) Not that it makes much difference at those sorts of numbers. Thankfully it wasn't too windy, so we only had about ten degrees of windchill on top of that.

(Huge - northern MN)

cheers

Jules

[Steve Firth]

Jings, is that near the tomb of the Unknown Norwegian?