Yanmar Marine Engine Help

Coolant in the Engine

Coolant: Is one of the most misunderstood and under serviced items in an engine. With a high performance engine IF YOU DON'T SERVICE THE COOLANT and OPERATE THE ENGINE PROPERLY you will have a SERIOUS FAILURE, see the photo.
This is a heat exchanger housing from a 4LH series engine. The core has been removed and what you can see is the water cooled exhaust manifold, an integral part of the housing. This housing has cracked and leaks coolant into the exhaust system. I borrowed this photo from a website where the writer blames the failure on galvanic corrosion and the use of aluminum components in the engine. This is not correct. The red circle highlights cavitation erosion (often called cavitation 'corrosion') of the hot exhaust manifold surface. I suspect the engine may have been filled with a conventional ethylene glycol based coolant containing silicate, nitrite, nitrate, borate, phosphate and amines, as has been commonly used for many years, and not serviced correctly. This type of coolant has a life of around 300 hours in this engine and if not replaced or serviced with SCA's (supplementary coolant additives) at recommended intervals, this type of failure will occur.
It is better not to use any additive at all if you can't service it properly. Extended high power OPERATION will also contribute to this type of failure. For coolant that has the best known hot surface aluminum erosion protection use Havoline® Extended Life Coolant, click HERE for their spec sheet as a .pdf file. ( 'right-click' and 'Save target as...' )
If you need Acrobat Reader to view the .pdf file, get it here.

Any coolant manufacturer willing to warranty an engine against cavitation erosion may send me their specification,in .pdf file format, and I will post it here.
This is a close up of a heatexchanger core from a 4LH-STE engine. Click the picture to enlarge it. This side is in contact with the fresh water coolant. The engine was using a conventional coolant that had not been maintained, hence the scale on the tubes. This is a common cause of overheating. The core needs to be cleaned in a bath with NON-ALKALINE cleaner - tell the radiator shop that the shroud is aluminum and will be eaten away if a caustic bath or similar is used.

The fretting erosion around the shroud is caused by the engine not being aligned with the prop shaft and the engine was observed nodding vigorously at idle. Although it looked OK at higher rpm the problem was still there, just going too fast to see.

Installation Tips

In turbocharged engines use only:
Havoline® Extended Life Coolant, DEX-COOL® Code number 7994, colour: ORANGE
You can safely use this product in any YANMAR fresh water cooled engine, follow the coolant manufacturers instructions for servicing. TEXACO No, I dont work there or know anyone that does, I just know what works!
Use de-ionized water (or clean rain water) and coolant, or buy the 50/50 premixed coolant.

Except in an emergency do not top up a system with water only. If you had to add water only to the coolant, replace the entire coolant package as soon as practicable.