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To flush, or not to flush?

Ian Perry

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After the much-lamented demise of the Toledo's original engine on the RBRR, I am currently planning to buy a S/H engine and put that in* - but of course that could have been standing for a while, could have had the same oil for 30k miles, could be full of gunk or simply bone-dry...

So, would it be a good idea to chuck some flushing oil through it, or chuck some thin-ish "normal" oil in, run it for a short while and then drop it back out, or just put some good quality multigrade straight in?

Are there any other things that the assembled brains would recommend before starting it for the first time, or after running it for a short while?


*SpitBitz have quoted me £225 for an engine (I assume MkIV) in "good serviceable condition" - with 28 days approval/warranty so long enough to get it clean, in, running, check compression and oil pressure etc. - and take it back if not happy. I assume it'll come with no ancillaries, but obviously all those can transfer over from the dead one, along with the sump (Spitfire and Toledo have the "well" at opposite ends).



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Ifit is a spit engine you will be swapping sumps anyway. So a good clean out then. 

Once fitted I would use some cheap oil for a short time  (enough to confirm the engine is OK etc) then drain, fit a new filter and decent oil. 

If it is a dolly engine, I think I would still be tempted to drop the sump and clean it out, for the sake of an hours work and a gasket. Usually a good bit of gunge lurking..

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Thanks, Clive. Considering the horrors in the bottom of the sump pan when I took it off (this despite it having had two oil changes in my ownership, and not counting the fragmented big end and piston skirt), I think that dropping the sump off is a good call on any engine.

Is there a particular good reason not to try a flushing oil? I would expect there to be a fair risk of gunged-up oilways and drillings, and a flushing oil should help clean that all out.

And I already have some :-)

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Given the terms of sale, I'm going to be a bit contrary. I totally agree with Clive on the "good clean out" while the sump's off but then I would stick in the cheapest oil you can find and fire it up. Drive for maybe fifty miles, assess the noises and smells. If all is good, think about whipping it back out for a proper clean out of the cooling system, new core plugs, oil flush and so on. If the initial test gives you the heeby-jeebies about its condition, send it back without spending your time and money on it.

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Thanks all.

I like the idea of thin cheap oil and a run up/about, then if the augurs are good a more comprehensive clean. I have a lot of (I think) 5W40, decent quality but I have lots of it (the hillclimb car uses it) so I wouldn't mind sticking a bucket of that in and chucking it away afterwards.

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  • 3 weeks later...

I was in a similar position, though probably worse as my engine has been sitting in a crate for 30+years 

In my case some of the oil has deteriorated to the point of clagging up in places to a waxy consistency that took some removing, and fearful of blocked oilways I asked the same question. 

One suggestion was to make a first fill of 50-50 light oil and diesel, pump it throughout with the drill down the distributor hole, leave to soak, repeat, etc etc. Did this over a few days,, then obviously drained it thoroughly  

Seems to have worked. Might be overkill for you. 

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