what is the best way to flush motor ?

Submitted: Saturday, Jun 19, 2010 at 13:16
ThreadID: 79475 Views:3490 Replies:7 FollowUps:1
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hi all
Just picked up a 1993 4.2 diesel gq for $1000 it is good nick with less than150,000k's.
Problem is it has a stuffed head on it and has been standing for about a year with a sump full of water and old oil. Luckily the guy who owned it was smart enough to remove the injectors and the injector pump so they are ok. have picked up a good head for reasonable price. once running what is the best way to flush the motor out ? got my doubts about engine flush you buy at the garage.
old time mechanic says fill sump with diesel run for a couple of days. that will clean all crap out of motor. but i don't know about that one. any comment would be appreciated.
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Reply By: Fab72 - Saturday, Jun 19, 2010 at 13:48

Saturday, Jun 19, 2010 at 13:48
Your mechanic was half right. We used to (at a Toyota Dealership) change the oil and substitute 25% of the overall oil capacity with diesel.

Run for a few days?????? Errr. NO. Run at idle for about 30 mins, then drain and refill with new filter and new oil. Then after 5000kms, do the filter and oil again. Make sure after 5000kms you do the filter, any loose stuff will fill that filter mighty quick.

Hope that helps.
AnswerID: 421417

Reply By: mechpete - Saturday, Jun 19, 2010 at 18:42

Saturday, Jun 19, 2010 at 18:42
if you fill the sump with diesel as the old bloke suggested you with save on oil
but you will be looking for a complete engine . what do you think is going to lubricate the engine ? not the diesel !!!!
AnswerID: 421444

Reply By: Fatso - Saturday, Jun 19, 2010 at 20:41

Saturday, Jun 19, 2010 at 20:41
Once upon a time when I was an apprentice fitter & turner my elderly & quite worldly foreman, who was a sugar mill engineer for many years, called us apprentices aside & explained to us that you never put any kind of solvent or thinner or degreaser in a machine to clean it once it is assembled.
It was in reference to replacing a stripped gear in a very large milling machine where a tradesman had directed another apprentice to wash down the gearbox with kero.
The theory is that oils have certain additives which give certain properties to achieve certain outcomes.
Adding kero or thinners or solvents or even diesel changes the characteristics of the oil.
When you add kero, or whatever, to your assembled machine it is imposible to remove all of it.
So even when you give this engine an oil change it will have traces of diesel interfering with the properties of the oil you put in.
What we ended up doing to wash the gearbox down was to use the properly gearbox oil prescribed by the manufacturer.
Diesel engine oil has all sorts of additives designed to first of all lubricate, cleanse & suspend foreign matter.
Diesel is a fuel.
I would put some good oil in it & change it frequently.
AnswerID: 421470

Follow Up By: burnsy - Sunday, Jun 20, 2010 at 18:15

Sunday, Jun 20, 2010 at 18:15
Hi Fatso
Did you do your time in a sugar mill as did I At Isis?
Just curious as I don't often come across people that mention mills

Regards Mike
FollowupID: 691935

Reply By: Members Paul and Melissa (VIC) - Sunday, Jun 20, 2010 at 10:24

Sunday, Jun 20, 2010 at 10:24
buy some cheap oil and filters. run it for 500 or 1000k then change it. do this a few times then run good oil and filter and it should clean up OK. DONT use diesel or kero as the old bush mechanics suggest. did this on recomendation of a mechanic many years ago and buggered a motor.
AnswerID: 421508

Reply By: trainslux - Sunday, Jun 20, 2010 at 10:30

Sunday, Jun 20, 2010 at 10:30
Please do not use kero or diesel in the sump and run the motor.
Having been a mechanic for many years, the only time I have seen this done was when the diesel mec's were going to pull down a high km engine, and wanted to save time in the cleaning bay.
They NEVER used it on servicable motors.
Just regular oil changes, and maintainence inc centrifuge services etc.

Ok, what I would offer you is this.
With head off, clean as much of the motor as you can, inc leaving the sump to drain.
Head on, rocker cover off, flush with diesel by pouring diesel down the sides of the head so it runs down the oil galleries and into the sump.
Leave it to drain fully, as yet you have not even cranked the motor over.
This will also flush out any debrits of head gasket and grit from cleaning the block surface that falls down the oil galleries.

Refit rocker cover and get engine ready to run.

Now, fit new filter, plug, oil and just run it with fresh oil for 15min at operating temp, drop oil, this should remove most of the moisture.
Also, when draining, leave the oil filler cap off for as long as possible, to allow the moisture to vent from the motor.

Next day drive it for a day, and drop oil.
Then at the end of the weeks driving, drop oil.
Then in a months time, drop the oil again.
By this time, not only the moisture, but soot, and crud etc should have been pretty much stripped from the insides by the detergents in the oil.

Best investment of 120 bucks you can do after replacing the head.

AnswerID: 421510

Reply By: kev.h - Sunday, Jun 20, 2010 at 10:46

Sunday, Jun 20, 2010 at 10:46
I know its a bit of work but I'd drop the sump off and clean it out in case it's full of crud and rust etc. i would not like to send that through the engine
Cheers Kev
AnswerID: 421512

Reply By: Member - Bucky - Sunday, Jun 20, 2010 at 12:58

Sunday, Jun 20, 2010 at 12:58
I believe there is a Castrol type oil that will do the job for you.
Not too sure what it is called, but at one stage I remember getting some oil from Autobarn or Repco that had a much higher detergent value, and dumping it at 500 kms.
I too, got advised not to use diesel to flush the motor, as it will remove "friendly carbons", from the motor as well, and cause major dramas.
The only time you would do this is just before stripping down a motor, and using new rings and bearings.


AnswerID: 421529

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