Cruising Speed/RPM

aimcarthur · Post by **aimcarthur** » 26 Aug 2007, 08:28

Hi guys,

Thought I would start a discussion on what is an acceptable rpm for long motorway trips. I seem to settle down at 3k rpm = 78mph. This seems a little high too me?

Is it ok to run a 1.9 TD for several hours like this? Engine wear? Would this cause the head gasket to fail early?

Cheers

Al.

citronut · Post by **citronut** » 26 Aug 2007, 09:38

i have always hear you should try fort around 2,500 rpm or a bit less, the usual cause of premature head gasket failure is the rad fan/s not cutting in when they should, or lack of coolant
regards malcolm

deian · Post by **deian** » 26 Aug 2007, 11:48

It does seem a bit high, what size tyres do you have?

My old 2.1td settled at 2600rpm at 75mph (if i can remember correctly, someone let me know otherwise).

My V6 settles at 2000rpm doing 60mph, but that has 4 gears and the gearox is suited to the high torque engine.

Regards,
Deian

aimcarthur · Post by **aimcarthur** » 26 Aug 2007, 11:52

I assume the standard ones, Mich. on at present with standard Aura alloy wheels. ( I have only just brought the car).

The ZX may be lower geared than the Xantia/XM?

deian · Post by **deian** » 26 Aug 2007, 13:09

If they are both the same engine, then they should be geared the same in my opinion, maybe the lower gears may have been geared lower in the xantia to cope with moving the heavier car. But top gear in the Xantia would be geared the same if not higher (for comfort/economy).

Can you confirm to us what size the tyres are? Unless the car has had a new dash at some point and there is some sort of coding plug that wasn't swapped to get the correct readings in the dials with the engine/gearbox/tyres combinations.

It's better to run the engine at lower speeds yes. If you do motorway miles often then please make sure the oil and coolant are in good condition and topped up, these are your best defences until you have worked out what going on with the high revs at 78mph.

howiedean · Post by **howiedean** » 26 Aug 2007, 15:23

aimcarthur wrote:Hi guys,

Thought I would start a discussion on what is an acceptable rpm for long motorway trips. I seem to settle down at 3k rpm = 78mph. This seems a little high too me?

Is it ok to run a 1.9 TD for several hours like this? Engine wear? Would this cause the head gasket to fail early?

Cheers

Al.

I'm assuming that your talking about the speed your speedo is showing? My Xsara's speedo is around 5 mph higher than that of my GPS reading. My previous Xantia speedo was spot on.
I seem to remember that my previous 1.9 td Xantia used to show around 3000rpm at 80mph which if correct is not far out from your car.

AndersDK · Post by **AndersDK** » 26 Aug 2007, 19:12

The TD is designed to run 24h/day at any normal load. Reving at 3K is perfectly OK at about 75-78-ish (120-125kph) cruising speed.
If you try get the revs down, the engine wont cope with the weight of the car at the same cruising speed.

Make sure the cooling system is in perfect condition. The fans will only be needed at low speed or traffic jams, as the airflow on the cruising vehicle is huge compared to the small breeze the blower fans can do at full pace.

aimcarthur · Post by **aimcarthur** » 26 Aug 2007, 20:23

Thanks, all.

Tried GPS this afternoon. Speedo is spot on. Forgot to check tyre size but will report tmrw morning. But pretty sure they are the normal spec. from looking at them.

Cooling system is ok so far. The previous owner, a colleague at work said that the radiator leaked three years ok, low coolant light came and alerted her to the problem. Radiator replaced and has not filled up the coolant since!

I intend replacing the coolant shortly (noting the make shift header tank issue in haynes1!), although chucked some neat coolant in for good measure.

I will live with 3k rpm!

Cheers.

MikeT · Post by **MikeT** » 27 Aug 2007, 19:42

aimcarthur wrote:Hi guys,

Thought I would start a discussion on what is an acceptable rpm for long motorway trips. I seem to settle down at 3k rpm = 78mph.

FYI, I held 3Krpm in 5th today and my speedo read 76mph

Post by **RichardW** » 28 Aug 2007, 15:52

3k rpm should equal 75mph in a 1.9TD. I have travelled 105k in the last 4.5 years in my two Xantia 1.9TDs - probably 1/2 will be on m-ways at exactly this speed - doesn't seem to stress the engine too much. Interestingly the first one (95 LX) the speedo was pretty much spot on. In the second one (97 VSX) the speedo is widly optimistic, reading >85mph @ 3k rpm - both are on 185/65/15 tyres. It seems the speedo in the new Xantia (HDi 110) reads about the same as the second 1.9TD (on 205/60/15 tyres). However, it's much longer geared, so 3k rpm on that will = 90mph or so, which is likely to attract the attention of HM's finest. Better borrow my mates GPS and time the speedo....

jamieclayton9 · Post by **jamieclayton9** » 28 Aug 2007, 17:24

On my 1998 xsara it does 78mph at 3k. Sounds about right really

lolingram · Post by **lolingram** » 30 Aug 2007, 18:36

Agreed 100%

The TD is designed to run 24h/day at any normal load. Reving at 3K is perfectly OK at about 75-78-ish (120-125kph) cruising speed.
If you try get the revs down, the engine wont cope with the weight of the car at the same cruising speed.

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Cruising Speed/RPM

Cruising Speed/RPM

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