Unusual deposits on my inlet manifold

I have been trying, and failing, to fix a poor running issue on my Euro spec 308 GT4 for many months. Symptoms are worse when the engine is hot and typically result in pops and bangs at higher revs. I have the cam covers off at present in order to check the valve clearances - all within tolerance - however with the covers off it is clear that I have some sort of deposit built up under the left hand carb, viewed from the back, on the rear bank which is not present on the right hand carb. Looking more carefully the left carb is also much dirtier and there is even a small amount of greenish liquid trapped in a well in the inlet manifold.

History and intuition tells me that these things might be important and might indicate a leak or other imperfection in my input circuits. However I assume fuel would evaporate cleanly and there shouldn't, hopefully, be oil this far up.

I assume liquid is dripping down from the carb onto the manifold but wouldn't rule out the opposite; with something leaking back out of the interior through the manifold gasket

Interested if anyone has seen anything like this before and even better if this might be linked to some sort of helpful intervention. I am tempted to replace the manifold gaskets between the carbs, spacer and manifold.

I have posted some photos below

Any thoughts gratefully received.


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The greenish liquid there is coolant, and the deposits that you're referring to are congealed and crystalizing coolant. I would take a hard look at all of the coolant lines and fittings. If you're having problems identifying where the problem is exactly, you can put dye in to the coolant system and then look at it with a black light, which usually makes things easier to spot. Looking at the overall state of things there, I imagine you'll probably end up replacing all of your coolant lines

 

You are in dire need of pulling both manifolds to fix the corrosion to both head and manifold surfaces. Last one I did the manifolds were so stuck to the corroded studs I had to remove the heads, rig them up in a drill press and drill out the studs with special vey long drill bits. The corrosion was so bad I felt lucky to save the castings. The corrosion worked its way well into the intake path sealing spaces.

 

This.. This right here..so much this.

 

Yep - spot on - struck me between the eyes after writing the post. So there is a coolant feed via a bridge to the centre of the two heads and I am guessing that feeds into heads via the inlet manifolds. Yep - spot on - there's clearly coolant coming back through the gasket.

Will certainly remove the inlet manifolds and report back - hopefully much easier than that experienced by Rifledriver but if the heads need to come off - or the engine out - then so be it. It's a fun and interesting way to spend a few weekends.

Is it possible that this explains poor performance when hot. Is it possible that as the coolant system comes up to temperature so coolant is making it into the inlet mixtures and suppressing ignition.

Thanks - pleased I posted - looks like we are getting somewhere.

 

Can this be prevented with more coolant changes?
Sacrificial anode from boating supply?

 

Not changing coolant frequently can corrode the metal, especially in the intake manifold/cylinder head mating surface. I had a coolant leak similar to yours. Mine had major corrosion which I fixed by adding many layers of an aluminum filler then sanding to make it smooth. Eventually, i got it to seal with the gasket and the leaks stopped. You have to remove the intake manifold and check both the manifold and cylinder head surfaces for corrosion. Also, the gasket that goes between the intake manifold and cylinder head had a modification which adds new holes to better circulate the coolant.

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Thanks Joe, very helpful, lets see what I uncover.

 

Now that you have discovered it, it is something you need to take care of as Rifledriver said. Its not going to get better, Only worse.

 

I have seen too many of these ...

 

My experience exactly. After careful cleaning I used aluminum filled JB Weld to fill in the corrosion damage and filed the mating surfaces flat again.

It's a known issue that is only discovered when the intake manifolds are removed.

 

Did that few months ago,
One was a nightmare, had to cut the seal all arround, verry long process. Other was more easy.
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Proper assembly to start with and regular changes of an appropriate coolant with distilled water.

 

Thank you - I do not want this mayonaisse!