1976 V12 engine cooling passages totally blocked up with crud

A couple months ago I purchased a complete used Pre-HE V12 engine and transmission from a 1976 XJ12L. It was only earlier today that I finally got around to examining the engine a little closer. The motor does spin when I put a wrench / socket on the front crank pulley however in checking it out I found that the thermostat housings both in front and behind the thermostats is totally blocked off with crud.

I have attached some photos to show this condition. I hope they are clear enough to show off this problem.

Any white powder on the ground that is lying on the floor around the thermostats and water outlets is what came out of the engine.

Has anyone seen this before? The engine did sit around for a long time out of the car after the guy I bought it from scrapped out the car due to excessive rust.

My next plan is to pull off the water rails that run along the top of the outer edge of the cylinder heads to see if the inside of the cylinder heads is also completely blocked up like this.

Any suggestions would be welcome.

Typical of a motor left to stand with water still in the system, just slowly work your way through & have good garden hose pressure to keep forcing it all out…the usual replacement of any housing - pipes & other fittings badly corroded… feel like i’m saying something you already know

The white crud are crystals formed out of the coolant not changed for some time. I pick up some of this in my Tefba filters (see in archives under filters) which still form in a clean system. They are capable of blocking a radiator. Hence the need for radiator coolant filters.

I had same situation with my 1958 saloon. To get the first drop of water through the engine I removed only external parts of cooling system (rubber hoses and heater circuit, intake and water pump) then applied high pressure to block tap outlet / inlet. Prolonged 8 bar of H2O was not enough so I used a pressure washer outlet. My engine was out so any popping block plug was not an issue anyway. After an hour or so I noticed some flow, so switched my input from high pressure to high flow. After some two days of pulsed cleaning in c.a. 3 Bar high flow of open circuit I switched to closed circuit with a garden pump and some chemicals including amidosulfonic and oxalic acid. These were not very corrosive and did help some with blockage but not great as it’s not a calcium deposit so does not dissolve quickly. Then I proceeded to removing block plugs. Wish I had a chemical method to dissolve this ugly stuff …

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I’m not a chemist, and I think we all may know some about the dissolved minerals in water. The two main minerals are calcium and magnesium, and neither mineral is found in that quantity in either tap water or well water. The general guideline (depending on what material you read) is very hard water is 180mg/liter. What is 180 mg ? Think of a coated aspirin some of us old guys take to keep your blood slippery. That’s typically 81 mg. Now think of 1 liter as roughly one quart.

A V12 has maybe 5 gallon capacity…1/2 of which should be anitfreeze. So 2 1/2 gallons (10 liters) water. With the above hardness, that’s 180mg/liter x 10 liters or 1800 mg. The equivalent of 22 enteric aspirin. But do we really put hard tap water in our vehicles ?

Steve’s engine has a lot of crud. Would be interesting to know if it was calcium and magnesium. The color looks right. So, if this engine had annual coolant changes, and somewhat hard water was used, what we are looking at is calcium ? 40 + years of hard water deposits ? SD Faircloth

I saw that very recently when I disassembled the V-12 from my Series III E Type for a refresh/rebuild, although mine was not nearly that bad. My engine had not been run in over 30 years, but remarkably enough there was still green liquid antifreeze in it. However, there was a lot of crystalization as well, that looked exactly like that. If mine is any pattern, the water jackets in the block are similarly crudded up and the head gaskets are likely deteriorated as well. I don’t know what your plans are for the engine, and do not know how effective a cleaning attempt would be without pulling the heads. I decided to go with a full rebuild.

I found those crystalized deposits are pretty hard material that clings to the aluminum with great tenacity, so unless there is a good way to chemically dissolve it with aggressive flushing, mechanical removal might be the only answer. Since I was pulling mine apart anyhow, I did not try the flush approach, but I can tell you that when I was cleaning the block it did not seem that the chemicals I tried did much to move the crystals, so a lot of mechanical removal was needed.

CLR is an over the counter chemical used to remove calcium, lime, rust from bath fixtures such as showers, tubs, sinks, toilets, etc. CLR for calcuim, lime, rust. Not sure about introducing it into an engine. Would be maybe informative to determine if it dissolves those engine deposits that were removed. SD

Thanks to all of you for the excellent feedback. I think in the long run at the very least the cylinder heads have to come off which as everyone knows might be a real struggle to do if there is this much corrosion or slag buildup inside the cooling system.

Earlier I pulled the water rails off the top outer edge of the cylinder heads so I could look down inside the ports in the cylinder head to see the of condition the inside of the cylinder heads. I took some photos of the four corners so I could share them here.

rear left corner (where the idle control valve would be)

front left corner

rear right corner

front right corner

Are there any coolant drain ports down low on the block somewhere? So I could try to flush stuff out of the block.

The chances are there will plenty of crud in the block, surrounding the top of the liners. Especially towards the rear of the engine where coolant flow is less
No option except to remove the heads, and good luck with that.


could you gather some of the crud in a glass container and try various chemicals, in the hope one of then could dissolve / soften the deposit ?

…and put some aluminium in the same container…
kind regards


I mentioned CLR as a possibility earlier.

Found this stuff just a bit ago…

Starbrite Descaling Engine Flush. Active ingredient appears to be “inhibited” and “enhanced” hydrochloric acid. Also contains oxalic acid. Label says it removes scale, calcium deposits, corrosion, salt, carbon buildup in your engine’s cooling and wet exhaust system. Use on aluminum is a hard NO.
SD Faircloth

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Hydrochloric/ muriatic with aluminum?

This bears repeating…

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The footstomper take away. Do not put anything in your XJS (or any aluminum block/heads engine) cooling system or lubricating system until you have read the label and ensured compatibility with aluminum.

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I believe the cylinder heads are a alloy of aluminium and magnesium, perhaps with some other ingredient, there is discussion about this in the archives

Once made the mistake of placing an item made of this this alloy in muriatic acid and it attacks it ferociously

I am not a metallurgist, but it seems to me the whitish powder that is part of the blockage issue is a result of oxidisation of the base metals taking place, they eventually can corrode, become porous etc etc

I believe the extent of the problem in regard to a Jaguar alloy cylinder head can be tested with a Brinell Hardness Test, details in the archives

Brinnell testing is for the hardness of the metal: these are the tests for corrosion resistance.

I was faced with cleaning that white stuff out of my cooling system and my first step was to figure out what it was. Everyone assumes it is calcium, so I took some and put it in hydrochloric acid, which causes calcium to fizz and dissolve. Nothing happened, the white crystals just sat there. I tried everything I had, including CLR and a half-dozen other similar products, but nothing touched it. My test procedures having been exhausted, my final guess was that it is aluminum oxide, which is pretty rugged and is used in making sandpaper. If any chemists can find out what dissolves Al2O3 we could get a more definitive answer as to what it is and whether it is even possible to remove it chemically without dissolving the rest of the engine.


The white powdery deposit on the surface may indeed be aluminium oxide, but to totally block passages, the deposit is too voluminous to be wholly sourced from the block itself - it has to be a precipitate from the coolant mixture. That’s evidenced by the fact that when it is chipped away, the cylinder head is still there underneath.

To get to the bottom of this, you’d have to look at the constituents of the coolant mixture and it’s chemistry/decomposition.

kind regards