Temperature in S1 engine bay

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As David says, Fan Yi; ‘why not’…:slight_smile:

However, why turn off the engine for testing - it can easily be done with the engine running. The exhaust temp should be the same for both branches of course, possibly indicating carbs not fully synchronized. It’s a minor detail - but the exhaust temps, A and B will vary widely with the driving - a prolonged full throttle the driving; downpipes will be red hot…:slight_smile:

Unless looking for some thing specific - these readings are not very informative. Checking water rail temp at the base of the dash gauge temp sensor - gauge should show that temp. And testing temp at water rail, top hose and bottom hose will give more interesting data on your cooling system’s performance - with the engine running of course…

As an aside; the two different readings at each point - did they vary that much during readings, or does it just represent instrument precision? Most IR’s are within less than a degree…

Frank
xj6 85 Sov Europe (UK/NZ)
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My car is the same as yours and is a very good performer. On the temperature gauge in the summer in Sydney it runs between the “A” and the “L” on the temperature gauge, for normal driving and never overheats. FWIW, Paul.

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Thanks for the info Frank. The temperature varies abit when I used the handheld IR meter to measure at different spots of the same part. Like the three branches of the front exhaust manifold. My water temp gauge stays at “o” to “r” of the “Normal”, so I wanted to find out how hot the engine bay is.

Thanks Paul. I enjoy driving the car. Have not worried too much about overheating yet. More concern on oil pressure at the moment. In my case, OP at idle drops as the oil temperature rises. After each hillclimb I do (30~35 degrees max now in Brisbane summer), OP can drop to about 10SPI when waiting at lights. I just shift it to “N” to increase the OP to about 20SPI. When I start the engine cold, the gauge always reads about 40~50 SPI. So I assume it is reading correct?

Correct. 10 maybe on the low side but more than enough. You probably use 20w50?

Jaguar only ever gave one spec - 40 psi @ 3000 rpm. Rule of thumb is 10 psi per 1000 rpm, with hot oil. Especially after a hill climb it will be! So your engine is perfectly fine.

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What he said. The 40psi at 3000rpm is noted in the competition handbook for e types, if not in other places. Paul.

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Yes, it is currently running 20w50. I have got some Penrite 20w60. Will replace the oil after 1000miles and see if the OP at high temperature get improved.

Thanks Paul, I heard the 40psi@3000rpm statement a few times but could not find that in my xj user manual.

Why? Did someone tell you thicker is better?

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I visited a local classic Jag engine rebuilding centre before I bought my car. Quite amazed by the owner’s work. He offers a 25 months/25000km warranty for all engine provided by his shop and no oil leaks. And for daily use, he recommends penrite 20w60, which may due to a long summer of 2/3 of the year we have here.

You don’t need it. And your oil pressure is fine. Don’t overthink this!
Of course if he says to use it, it’s not doing any damage. Why not.

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Engine compartment temperature is of no significance for engine health, it will vary with air temp - the coolant is what keeps the engine suitably cool. Measuring the temp at the water rail at the base of the temp gauge sensor - it’s what the temp gauge should show. And reflects the general state of your cooling system…

Oil temp is interesting in its own right, but is more difficult to supervise - unless a gauge with suitable sensor is fitted. Oil gets thinner with increasing temps, hence the variations in oil pressure - the hotter the thinner. The multigrade numbers, like 20/50; the first denotes that it flows like a ‘20’ when cold - and lubricates like a ‘50’ when hot - but still; ‘the hotter the thinner’. Too high viscosity is counter- productive in a cold climate - and there is more to engine lubrication than oil pressure…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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And remember: One common problem is oil running too cold. It needs to get hot enough to boil off any moisture in the crankcase via condensation or whatnot. If the moisture sits in the oil, the oil breaks down and becomes acidic, I think – something bad. Pits bearing shells or something. Common problem with cars that are never driven more than five minutes at a time, since the oil never gets hot. Years ago Michael Neal told us a popular mod to some model of Lamborghini was to install a thermostat in the oil cooler to keep the oil from running too cold.

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HI,

This may be a very different case, I have never had oil pressure problems in my 6-cyl Jaguars (well, the MKV pushrod engine with it’s adjustable oil pressure is another story) all 20W-50 oils and even the modern 10W-40 oils have worked well in the XJ6 4.2, although I was told by a specialist that I should not drive it at 180km/h+ (why? :slight_smile: ) as he says it will not last long if I do. (have 40.000+ kms now after a complete rebuild).

BUT I did have a problem with generic “classic” 20W-50 oils in the V12 E-type. Not in normal driving and not even when it got hot (we had several weeks of over +30°C back in 2018). The problem was that when I was driving south through Denmark and Germany and from Puttgarden to Hamburg there was very little traffic so we could floor it. Beyond 190km/h (120mph) the oil pressure would start to drop, and I mean to almost nothing, very alarming. Once I slowed down to 180km/h the pressure started to raise up again.

We had a service done for the car (there were some other small problems as well) in Switzerland at GB Dönni Classic Car in Roggliswil and after they fixed the other issues and put in Penrite 10W-60 “Classic Light” there was no problems with the oil pressure anymore. On our way back we happily did long stretches at over 200km/h (125mph), topping at 229km/h (according to the GPS, 142mph) near Celle in Germany and oil pressure was constant and did not drop below 40psi anymore.

YMMV. :slight_smile:

Cheers!

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Hi,

Oh, it wasn’t standard? I think on the 456GT there are at least two oil thermostats, which direct the (dry sump) oil system so that the oil warms up quickly and is then cooled or warmed as needed. In the Jag V12 the heat exchanger in the sump also does that although not as sophisticated.

For the XJ6 an oil cooler is not a bad idea to install if you live in a hot climate and/or want to drive fast. :slight_smile:

Cheers!

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That is very interesting story. I don’t think we can legally get to such speed on Australian hi-ways. Penrite 10W-60 is full synthetic, and they claim to provide improved oil pressure at hi oil temperature. I may consider this if I ever gonna do track days or more serious hillclimb.

Hi Frank, is it located at the intake side behind the SU carbs?

Hi,

Sure, also for us in Finland, 120km/h is max in the summertime, 100km/h on most roads I drive on, or even lower. That was in Germany where I had the V12 stationed for two years and now it’s the XJ6C’s turn. But it is true there are many variables when it comes to motor oil. With my first car (Ser 1 4.2L E-type 2+2) the only issue was the amount of oil it would burn and drip. :slight_smile:

Cheers!

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Yes, the sensor near the thermostat that has a wire to the temp gauge. The sensor is a thermistor that provides variable temperature-dependent resistance to current flow through the gauge (which is a fed a constant 10V from the instrument voltage regulator). The higher the temp the lower the resistance (opposite to usual). The greater the current through the coil inside the gauge the hotter the bi-metallic strip becomes and the more it bends to move the needle along the scale.

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Remember that viscosity is measured at a specific temp, Fan Yi - usually 20C. But when hot, say 140C, the oil is considerably thinner, probably in single figures. And when cold, like -40C, viscosity is considerably higher; a 20/50 will behave like a ‘20’ oil at -40 - which is not quite like treacle, but rather thick. This is the sole reason for the much higher oil pressure with the engine cold. So a ‘10’ is better for starting at that temp - while the ‘60’ part will behave like plain ‘60’ at 140C…

The only purpose of oil pressure is to push oil through the bearings - where it leaks out, to be continuously renewed. This both lubricates and cools the bearings - without this circulation the bearings/oil would gradually heat up and seize. The bearing clearances allows an oil film to form, and is the quality of the oil that prevents metal to metal contact - which will wear, and burn out, bearings. A good ‘10’ is no more prone to breakdown than a ‘20’, but with a lower oil pressure The oil pressure in itself plays no part in preventing film breakdown; it just maintains the flow - the actual pressure on the bearings is in the region of several hundred pounds…

As an aside; in the old days, with single grade oils in a cold climate; changing oils for summer and winter viscosity was routine. And in a climate of extremes; it is still a good idea for reasonable starting and cold lubrication even with multigrades. However, few of us live in such an environment…:slight_smile:

Arguably, synthetic oil is more stable, but oil quality is still the crucial factor. Mere synthetic does not in itself guarantee the quality - though all major manufacturers are very conscientious; it is the quality that guarantees the brand, not the other way around…

Frank
xj6 85 Sov Europe (UKNZ)

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