Corrosion inside engine block water jacket

I have had a recurring problem with the coolant used in my Series 3 diesel engine soon losing its blue colour.

When refilled with fresh coolant (40% concentrated antifreeze mixed with de-ionised water) it will soon lose the blue colour altogether and look clear with a slight rust brown colour

The engine was rebuilt by a well-known company in 2014. As part of the rebuild, the water jacket was apparently steam cleaned and flushed to remove any loose rust.

I know someone who has an old Shogun with the 2.5 litre diesel engine. The Shogun also has a cast iron engine block and brass radiator similar to the Series. In the past I have helped them flush out the system and replace the coolant. The same type of coolant and mixture ratio in that engine and radiator seems to keep its blue colour.

Is there any flushing chemical or extra additive that will reduce or stop the corrosion inside the Series cooling system?

It is the job of a good quality coolant to prevent corrosion. Just swap it for fresh. I prefer ready use as no messing about getting the mix right.

Try upping my your coolant to 50% as well

i should be checking head gasket

Thanks for the replies.

I used to be able to get de-ionised water for free so preferred to mix it myself to save paying money for water. I simply pour 600ml of concentrated coolant into a 2 litre plastic kitchen jug, then add water up to the 2l mark. When checked with an antifreeze tester this mixture is apparently safe down to -24c which the vehicle will never see in UK conditions.

jamesmartin said:

i should be checking head gasket

Click to expand...

There is no sign of any oil in the coolant or coolant loss.

There are also no white deposits in the oil.

Webley1991 said:

Thanks for the replies.

I used to be able to get de-ionised water for free so preferred to mix it myself to save paying money for water. I simply pour 600ml of concentrated coolant into a 2 litre plastic kitchen jug, then add water up to the 2l mark. When checked with an antifreeze tester this mixture is apparently safe down to -24c which the vehicle will never see in UK conditions.


There is no sign of any oil in the coolant or coolant loss.

There are also no white deposits in the oil.

Click to expand...

i was thinking gases in cooling system

Webley1991 said:

Thanks for the replies.

I used to be able to get de-ionised water for free so preferred to mix it myself to save paying money for water. I simply pour 600ml of concentrated coolant into a 2 litre plastic kitchen jug, then add water up to the 2l mark. When checked with an antifreeze tester this mixture is apparently safe down to -24c which the vehicle will never see in UK conditions.


There is no sign of any oil in the coolant or coolant loss.

There are also no white deposits in the oil.

Click to expand...

Iirc 50/50 is good down to -30degc, but more importantly the anti freeze contains corrosion inhibitor.

I have always run 50/50, and in some right old dogs to, never had one with brown coolant yet.

I think I would drain and refill with plain water, run it drain and repeat each day for say a week, then go back to 50/50 and see how you get on.

You initially said engine restorer steam cleaned the engine would have thought it needed some sort of chemical to clean it. Series 2 club forum recomend putting a dishwasher tablet in run it like that for awhile then drain flush and refill.

Blackburn said:

You initially said engine restorer steam cleaned the engine would have thought it needed some sort of chemical to clean it. Series 2 club forum recomend putting a dishwasher tablet in run it like that for awhile then drain flush and refill.

Click to expand...

steam cleaning is normally a good way of cleaning blocks once core plugs are removed

lynall said:

Iirc 50/50 is good down to -30degc, but more importantly the anti freeze contains corrosion inhibitor.

I have always run 50/50, and in some right old dogs to, never had one with brown coolant yet.

I think I would drain and refill with plain water, run it drain and repeat each day for say a week, then go back to 50/50 and see how you get on.

Click to expand...

It's not muddy brown as such. It loses the blue and becomes clear with a slight brown colour when drained out into a clear container.

Unfortunately I can only get over to it about once a week as its not stored at home. Looking back I now regret not more of these jobs while I was off work during the lockdown earlier in the year.

I will drain it all out, flush with a hose, refill and see how it goes.

Mines always like soup. Still cools though.

Webley1991 said:

It's not muddy brown as such. It loses the blue and becomes clear with a slight brown colour when drained out into a clear container.

Unfortunately I can only get over to it about once a week as its not stored at home. Looking back I now regret not more of these jobs while I was off work during the lockdown earlier in the year.

I will drain it all out, flush with a hose, refill and see how it goes.

Click to expand...

If its losing the blue it must be to weak, I dont drive my 90 or the series much at all these days, yet the coolant is still blue in both of them.

Webley1991 said:

Thanks for the replies.

I used to be able to get de-ionised water for free so preferred to mix it myself to save paying money for water. I simply pour 600ml of concentrated coolant into a 2 litre plastic kitchen jug, then add water up to the 2l mark. When checked with an antifreeze tester this mixture is apparently safe down to -24c which the vehicle will never see in UK conditions.


There is no sign of any oil in the coolant or coolant loss.

There are also no white deposits in the oil.

Click to expand...

that’s only a 30% mix.

up it to 50/50 coolant to water.

don’t worry about the temperature thing, just think the more coolant the less diluted the corrosion inhibitors will be

I meant to type 800ml Antifreeze to 1200ml water. That is a 40% mix as the container recommended.

As far as I know, 50% is the highest percentage of antifreeze that should be used, as water is apparently better at transferring heat than the antifreeze.

Webley1991 said:

I meant to type 800ml Antifreeze to 1200ml water. That is a 40% mix as the container recommended.

As far as I know, 50% is the highest percentage of antifreeze that should be used, as water is apparently better at transferring heat than the antifreeze.

Click to expand...

yep 50 is the highest ‘normal’ level. It’s also easier to calculate lol.

try 50/50 - it won’t do any harm whatsoever and won’t have any negative effects on the engine - and see how you go with the colour. Mine goes in blue and comes out blue a couple years later.

I'm not seeing a problem. "50 year old vehicle makes coolant dirty". Do we have any evidence that a Series did not do this from new? I've driven old Britsh vehicles for many years, coolant in iron engines gets dirty.

I would use one of the flush products you can buy. Leave it in for an hour to get fully hot and get round the full system. Leave it to cool then drain. Flush with a hose pipe until the water runs clear, then fill will coolant

kermit_rr said:

I would use one of the flush products you can buy. Leave it in for an hour to get fully hot and get round the full system. Leave it to cool then drain. Flush with a hose pipe until the water runs clear, then fill will coolant

Click to expand...

I can’t be bovered

It seems like a good method for flushing would be to remove the top thermostat housing and thermostat to get a good flow of water into the block with a hose. Is that the normal way to do it?

rob1miles said:

I'm not seeing a problem. "50 year old vehicle makes coolant dirty". Do we have any evidence that a Series did not do this from new? I've driven old British vehicles for many years, coolant in iron engines gets dirty.

Click to expand...

As the engine was newly rebuilt to as-new in 2014, I would hope that it had been well cleaned out.

The Shogun I mentioned in my first post also has a cast iron block, and the coolant in that doesn't appear to get too dirty compared to the Series. The Shogun is nearly 30 years old itself and has never had its engine rebuilt.

Don't forget the radiator and cab heater, if you have one, can be full of gunk