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Acceptable oil and coolant usage for 3.8 engines when run moderately hard
So when being used on a regular basis, what should I be expecting to see with my Mk 2 regarding oil and coolant usage? The car's engine is said to have less than 10k miles, and runs very strong, and is driven in a "spirited" manner, meaning fairly regular hard acceleration, with cruising rpm (at least until the o/d is fixed) running at +/- 2500.
As well as amount used, what is the consensus on where to maintain the levels of each vessel of precious fluid?... oil down half a quart from full?... a full quart? And coolant...should it be kept topped up, or will it use less if it's maintained a bit lower?
Fwiw, this car has either blown out or somehow consumed nearly a quart of coolant in somewhere north of 200 miles - I've yet to see any evidence of it consuming it, as it's 100 percent coolant, so no cream under the filler cap or air filter assy.
The owners manuals are quite clear about the regular checking of both, but I'm both curious and concerned what the acceptable ranges are, especially after experiencing my S1 XJ6's oil and coolant use before discovering it had six cracked liners...
Thanks in advance for any experiences and recommendations!
Last edited by Chris Scott; 12-13-2023 at 11:28 AM.
The XK engine has a reputation of using oil but mine is a rebuilt engine, no oil leaks and I hardly ever have to top the oil up between services. May be a litre of oil every 1000 miles. Others has different stories. I personally would say most top ups are required because of leaks rather than the engine burning oil especially in a rebuilt engine. Maybe a worn one but not rebuilt.
As for water when I firsts started running my car, after the restoration when everything was standard I frequently would pull up after a drive to see a pool of water emanating from the radiator over flow pipe on to the road or even steam coming from under the bonnet on the left side which again was steam coming from the over flow pipe. I would constantly have to top up the water before each trip as the level in the radiator was low. This is perceived to be normal but to me unacceptable. All it is, is the water expanding in the engine and forcing it past the radiator cap in the form of steam or pressurised water. I cured this by fitting an expansion tank from an MBG. It i fits neatly on the left inner wing where the voltage regulator used to sit but was removed when I changed to an alternator. The tank is brass so fits in perfectly with my brass radiator top. In the two or three years I have been running the expansion tank I have yet to have had the need to top up the fluid level. Any over flow or steam goes to the expansion tank and when the engine cools it draws the fluid back from the expansion tank into the radiator.
I use the tank of the rad as the expansion tank, only filling to the bottom of the filler "round".
Many have added an additional expansion tank with an updated filler cap that allows coolant to be drawn back into the engine, and this works well enough.
If one wants to keep the original system, just don't fill it to the top; by filling the rad to the bottom of the filler orfice, the top of the tubes will be immersed in coolant, and that's enough.
Oil consumption varies wildly depending on oil scraper ring design employed on an accurately rebuilt & properly run-in engine. I would consider Cass' experience of "a litre of oil every 1000 miles" as normal. The 3.8 engine always used more oil than the 3.4.
Comment from scribe James Taylor: "September 1962 ~ That same month, the 3.8-litre engine’s reputation for burning oil was tackled with new piston scraper rings".
I use the tank of the rad as the expansion tank, only filling to the bottom of the filler "round".
Many have added an additional expansion tank with an updated filler cap that allows coolant to be drawn back into the engine, and this works well enough.
If one wants to keep the original system, just don't fill it to the top; by filling the rad to the bottom of the filler orfice, the top of the tubes will be immersed in coolant, and that's enough.
Although I agree with you Jeff that using the top tank of the radiator as an expansion tank is acceptable I found that steam was still escaping and lowering the water level so I then found it hard to gauge how far down the radiator the water level was. I could not see the top of the water so ended up throwing a little bit in each run to "Make Sure". With the expansion tank I have not had to top up the water level since I fitted it and it gives me peace of mind that I only need to check the levels every month.
I need to rig up something like yours Cass but under the wheelarch as I still have a regulator in the way. I'm tired of my expensive long life coolant being spewed on the road.
I need to rig up something like yours Cass but under the wheelarch as I still have a regulator in the way. I'm tired of my expensive long life coolant being spewed on the road.
If you remember Glyn I first had the bladder bag as we called it under the front wheel arch. It was a windscreen washer bag that I bought for £10 and hung under the wheel arch. It worked fine for a couple of years but then the detritus from the front wheel slowly destroyed the plastic bag and rather than replace it I went for the brass tank. Under the bonnet room is at a premium and the expansion tank really needs to be around the same level as the top of the radiator. I was lucky that I moved to the Dynalite alternator and could remove the voltage regulator from the inner wing which gave me the room I needed to fit the brass tank.
There is room under the wheel arch behind the front light on the inner wing. It is difficult to get to if placed high enough but once it is fitted there is no need to get to it on a regular basis as you won't need to top up the fluid level and if you do you can just do it via the radiator when checking the levels. In your case if painted black it would be out of sight and not interfere with your originality.
Spot on Rob. Now that the car has been rated I'm not as bothered about originality. In the new year I will be fitting my Nardi 15" wood-rim steering wheel as an example. (One of 4 made by a chap at Nardi with the Moto Lita hub/mount)
Last edited by Glyn M Ruck; 12-14-2023 at 04:55 AM.
I'll agree with everyone. Jeff's description is how the coolant system is supposed to work and may well in some cases. Fill the coolant to a little way above the bottom of the filler tube or fill it to the top and leave it after the top pint or so comes out. It didn't work well with my car. Somehow through air entrainment or whatever, it continued to lose a little water. Cass's scheme definitely works. That tank is quite small, looks original (in black or in brass) and is (or was) widely available as several British Leyland/BMC cars used it. It may be convenient sometimes to have it level with the top of the radiator, but (I think) it should work as well if placed lower so long as it has a (low) pressure cap.
We discussed oil consumption not long ago. Anything less than a pint every 100 miles is OK for an old XK, especially a 3.8.
The XK engine has a reputation of using oil but mine is a rebuilt engine, no oil leaks and I hardly ever have to top the oil up between services. May be a litre of oil every 1000 miles. Others has different stories. I personally would say most top ups are required because of leaks rather than the engine burning oil especially in a rebuilt engine. Maybe a worn one but not rebuilt.
As for water when I firsts started running my car, after the restoration when everything was standard I frequently would pull up after a drive to see a pool of water emanating from the radiator over flow pipe on to the road or even steam coming from under the bonnet on the left side which again was steam coming from the over flow pipe. I would constantly have to top up the water before each trip as the level in the radiator was low. This is perceived to be normal but to me unacceptable. All it is, is the water expanding in the engine and forcing it past the radiator cap in the form of steam or pressurised water. I cured this by fitting an expansion tank from an MBG. It i fits neatly on the left inner wing where the voltage regulator used to sit but was removed when I changed to an alternator. The tank is brass so fits in perfectly with my brass radiator top. In the two or three years I have been running the expansion tank I have yet to have had the need to top up the fluid level. Any over flow or steam goes to the expansion tank and when the engine cools it draws the fluid back from the expansion tank into the radiator.
Very nice work there mate...
So a couple of things...one, is I was incorrect with the RPM's I'm running at cruising speed....right around 2200 - 2300 is where it seems happy, which iirc is just over 70mph - the gauge wiggles a bit, so it's hard to say.
The other is that it has an after-market alloy rad, which is vented back almost to the firewall...I think I'd like to get some form of a header tank in there as well, as it just seems stupid to allow the stuff to go to atmosphere - it ain't cheap!
...and regarding rpm's, Though it gives every indication of wanting to, I've thus far not pushed this car much (if at all) over 3k. The top speed of these cars seems to suggest that even with an o/d 120mph would be spinning these engines way up there...what say you guys?
I'll be back in L.A. getting the carbs/fuel system issue sorted after the holidays, and then I shall be putting some time on the engine and will have some more accurate figures regarding it's performance.
Thanks!
Last edited by Chris Scott; 12-15-2023 at 10:15 PM.
...and regarding rpm's, Though it gives every indication of wanting to, I've thus far not pushed this car much (if at all) over 3k. The top speed of these cars seems to suggest that even with an o/d 120mph would be spinning these engines way up there...what say you guys?
At 120mph with OD you are into the red zone i.e. above 5500RPM with a 3.8 litre. If you look at the horrific fuel consumption some of the journalists achieved when the cars were new they spent plenty of time up there & never broke one. In racing they were revved over 6000RPM.
My old car was happy to cruise all day at 3,000 rpm in o/d top. That's 80 mph. In many Mk2 cars and certainly mine, the only way of knowing the car is traveling at 80 mph is the reading from the tacho as the speedometer needle is in a double frequency oscillation. I eliminated the oscillations once by shuffling the speedo cable, but after two or three weeks it came back. Peak power at the rear wheels is at 4,500 rpm or 120 mph. That's as fast as my 3.4 has my car has achieved (on an unlimited stretch of the German autobahn). There was a lot of turbulence noise from the door windows and I lifted off when we started to catch up with other vehicles.
Glyn, I think your rev/min is in direct top.
You can drive a Mk2 without exceeding 3,000 revs. It feels like a nice, reasonably sophisticated, old classic car and you'll never imagine it's other side. Push it above 3,000 revs, and everything changes, it becomes the powerful, road burning sports saloon that made it special in its day.
Peter. what gearing are you running? While I agree with your peak power reading that can't be 120mph. I'm talking S Type numbers for a 3.8. All synch gearbox plus compact OD 0.77 to 1.
The S Type does not achieve peak speed in direct top ~ it achieves 110mph in direct top. I have a book of every known road test on the S Type which includes SA's CAR Magazine. (see post below) ~ BTW ~ the S Type is the most aerodynamic of the compacts.
Mk2 diff ratios.
Last edited by Glyn M Ruck; 12-16-2023 at 04:51 AM.
"Again in the person of John Bolster, Autosport tried out an overdrive model rather less than a year later for their issue dated 14 May 1965. The car was EDU 482C, which also figured in other road tests of the time. In Bolster’s hands, the car took just 10.2sec to reach 60mph from rest and went on to a maximum of 122mph (196km/h) – incidentally demonstrating just how much automatic gearboxes of the time harmed both acceleration and maximum speed. The maximum of 110mph (177km/h) achieved in direct top showed exactly how valuable that overdrive was for highspeed motoring, and Bolster commented that the car still felt ‘wonderfully lively on top gear’."
110mph was achieved in direct top.
The Automatic in Bolster's hands:
"recording a 0–60mph time of 11.6sec and a mean maximum speed of 115.4mph (185.7km/h). ‘On fast roads,’ he noted, ‘the S-type cruises in restful silence at over 100mph.’"
Last edited by Glyn M Ruck; 12-16-2023 at 04:36 AM.
Glyn, My car is a 3.4 Moss with overdrive and 3.77 rear axle. Maximum power at the road wheels at 4,500 rev/min is what I've seen quoted for standard Mk2s and E types on chassis dynos. The difference from the higher engine speeds quoted by Jaguar probably arises from the original figures being gross (no water pump, fan, etc) and transmission losses. The 80 m/h at 3,000 rev/min at 120 m/h at 4,500 rev/min for manual with overdrive MK2 and S type cars in overdrive top are numbers given in the handbooks and service manuals. They match calculations (they are calculated) and road experience.
If you say so ~ the manual agrees with you at 4617RPM = 120mph. I've been in a friend's original S Type that is very well looked after with a nice patina but rebuilt engine with about 20,000 miles on it. He drives it like he stole it. With a steady speedo, rebuilt by Orlando's favourite bunch, at just over 120 indicated mph it was just into the red on the tacho with OD engaged. Why I can't answer.
Maybe his car ended up with a Daimler Sovereign rear axle which caused a rise in revs. It is a very late car and they messed with Daimler diff ratios near the end of production.
Last edited by Glyn M Ruck; 12-16-2023 at 08:37 AM.
12-13-2023, 11:23 AM
Acceptable oil and coolant usage for 3.8 engines when run moderately hard
