Fuzzy radiator coolant

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NFCN

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Dear all

Towards the end of last season I started to notice that the coolant in the radiator of my engine was becoming a bit 'fuzzy' - ie, the liquid was frothy and white on top, and was beginning to overspill from time to time causing staining around the radiator cap.

I am suspecting that seawater is getting in somehow. The engine runs fine but it is slightly worrying. The engine is a 1980 Thornycroft T90 on board my Moody 33 Mk II.

I attach a photo. Can anyone offer a potential diagnosis?

Many thanks

Nick
 
I don't know your engine but it could be a blown head gasket, I've had these symptoms in my car some time ago and needed the alloy head skimming where corrosion had affected the head seal. Presumably you have topped up with the correct proportions and Antifreeze specification for your engine. The heat exchanger if fitted is normally separate from the raw water so not sure if any mixing would behave as your symptoms; as it is coming from the radiator cap there must be excess pressure there, like overheating, to exceed the prescribed psi of the cap. All guess work though, hope its something simple. The overflow tube looks flattened too. Is 7psi the correct one for your engine?

ianat182
 
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It is normally the case that the coolant pressure is higher than that of the seawater system, making it impossible for seawater to get in. However, a few cases discussed in these pages show that it can happen if:
a. the exhaust manifold is partially blocked, increasing the seawater pressure, and
b. the heat exchanger has not been assembled quite right, leaving a leak path at the O-rings.
However, as others have said it looks rather like high pressure in the coolant, which implies a gasket failure or a crack. Automotive repair shops have a range of tricks to detect the cause of this type of problem.
 
NFCN,

It could also be caused by a partilly blocked cooling water injection point into the exhaust. The raw water pump can generate a very high pressure.

I had this on a Thornycroft T80. The back pressure in the raw water system eventually found it's way into the coolant blowing it out past the pressure cap.

The coolant then became a mix of fresh water, salt water and antifreeze. By the time I discovered what was happening I had a bilge full of hot coolant.

Yours may be the early signs.
 
+1 for a blockage in the exhaust injection bend. Remove and check that the outer core is clear. If not it will back-pressure and allow salt water into the heat exchanger. It can get quite spectacular when really blocked.

Regards
Donald
 
Thank you all for your advice. At the start of last season I replaced the water injection elbow and had a good look at the exhaust system, which wasn't blocked up. Have only done 100 or so hours since then. I am thinking more that it might be a head gasket leak or a crack...
 
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