Welcome to our resource for MG Car Information.



TR parts and Triumph parts, TR bits, Triumph Car Spares and accessories are available for TR2, TR3, TR3A, TR4, TR4A, TR5, TR6, TR7, TR8, Spitfire and Stag and other TR models are available from British car spares and parts company LBCarCo.

Triumph TR6 - Rebuilt engine break-in oil

I have completed rebuilding my engine, including new piston rings, deglazed cylinders, new main and conecting rod bearings, new cam etc. It started and ran immediately, and runs smooth in my garage (no road miles yet). However, I inadverdently put 5w20 oil in her instead of 20w50 (there are too many cars in my garage all with different oil requirements). Any comments weather this is too light for break in. I know it is only $15 bucks to change out, but if 5w20 won't do any harm for a 100 or so km, then I'll leave it and change in a week or two. Any advise much appreciated
Pete Russell
Pete Russell

I rebuild my engine last winter and started it this past april. My british-car Knowledgeable guy (20+ years experience) suggested me to put 10W30 for 500 miles (no rpm higher than 3000 for 500 miles!) and then change oil, filter, adjust valve clearance and retorque head. I have now more than 1500 miles and it runs just fine. Just my 2 cents.


Marc Girardin
69 TR6 (now with 104 hp instead of 50 mice-power!)
Marc Girardin


I remember this subject coming up regularly on the MGB BBS. The consensus was to use a regular mineral oil, preferably lighter than normally recommended. On no account use a synthetic oil since this delays running in. Another point often mentioned was that when a new camshaft had been fitted, the engine should be run at around 2000 - 2500 rpm for 20 minutes on first restart. This is to avoid glazing of the cam surfaces. I did this when I installed a UK rebuilt engine in my MGB in 2002 and there was zero oil consumption and very good oil pressure when I sold it last year with 10,000+ miles added. I recognise that TR6 engines are not the same as MGB's however assume that the principles still hold.


75 TR6
B.J. Quartermaine

I ran 20W50 in my TR6 right after rebuild, this resulted in an oil pressure in excess of 70 PSI at idle. I asked the engine builder about this and he thought it was too high, he recommended 10W30. This change brought the idle pressure down to <50 PSI. After a couple of thousand miles my pressure is starting to drop slightly and I may change back to 20W50 if the idle pressure drops below ~30PSI. AFAIK this drop is normal as the engine loosens up. It certainly seems to be getting stronger and smoother as the miles go by.
On another note: I bought a couple of rare earth magnets from Lee Valley for the oil filter and oil pan. I have changed the oil three times since the rebuild and cut open the filter each time. There has been a fine slurry stuck to the can each time but so far no chunks, fingers crossed!

Don Ho's another 2 cents. When I finished my rebuild I started it with 10W30 and ran it around 1500 to 2000 RPM for twenty minutes to break in the cam. After the initial run I drained that oil out and replaced the filter. The immediate oil change was recommended to me by an engine builder. It made sense to me since there is the potential for stuff being in your oil after the first run...stuff like heavy bearing lube, dust and stuff that may have gotten in during rebuild, gasket sealing material...whatever.

After that I went right to 20W50..mainly because the Triumph spec. bearing clearances are a bit generous and I was on the upper end of the spec. That's probably why they specify 20W50 in the owners manual.
But if your bearing clearances are pretty tight then 10W30 may be fine.

I agree with Don Ho, If the pressure is somewhat low with 10W30 go to 20W50. Or the reverse...if 20W50 gives too high pressure readings then drop down to a lower viscosity.

When I did my rebuild I searched the web and asked experts this same question about initial oil viscosity. I got as many different answers as the number of experts. I just went with the recommendations that made the most sense to me.

HP Henry Patterson

if you are just idling in the garage it will be fine .
You have gone to all this work and expense and $15.00
is at stake, change over to standard 20/50, it will take longer to break in but what's the rush.
You don't want metal hitting metal.
Christopher Trace

Thanks all for your thoughts. I also did some research on the net, and found one site that cautioned about older designed engines using lighter oils like 5/20. Apparently they do not have the shear strenght at high temps, can break the oil film, and cause problems. So, I changed out the 5/20, and have put in 10w30. The oil pressure at idle is about 40 psi, and although I have only taken it up the street at max 2000 rpm, the pressure at 2000 rpm is 75. I think I will stay with this oil, and Henry, as you did, will change out after 100-200km to 20w50.
Thanks for the comments.
Pete Russell

I've used 10w-40 since my rebuild 15k miles ago. Remember, the high oil pressure is the result of back pressure - thicker oil doesn't want to flow into the tight gaps easily, so it takes more pressure to get it in there. You don't want to get to the point where the oil pressure relief valve has to open to keep the pressure in "range" - oil's being by-passed around the bearings when that happens and a high pressure is just fooling you. Unless you know where the RV opens I'd say it's better to have a slightly lower oil pressure (40-45 psi) with a lower vis oil than a high pressure with a 15W-50.
Brent B

This thread was discussed between 27/06/2006 and 28/06/2006

Triumph TR6 index