cracked block

88_rinker_v170

I have an 88 v170 the 3.0 that was originally in it had a cracked block beyond repair so I found a 2.5 out of a junk boat we had and I pulled it out and before dropping it in my boat I put it on the stand and planned on putting a gasket kit on it rebuilding the carb and just freshen it up. I drained the oil and as soon as I saw the milkshake my stomach dropped. I pulled the manifold and no crack at all I pulled the head no crack at all I stripped all the paint off the block and no crack the cylinders all looked great same with the pistons. The crank some how was clean as well. So I dumped a gasket kit in it and dummped about 5 qts of used oil in it and let it drain just to flush everything out then I added my fresh oil and filter. And it turns over by hand freely. What would cause milky oil in this situation? Am I safe to finish my project or should I just find a new engine?

youstolemybeer

how long did the engine sit before you rebuilt it, was it outside exposed to the elements? rain water and condensation can make the oil milky. Also check the thermostat, it could be stuck open, that will cause milky oil also because the oil cant get hot enough to burn off condensation.

aero3113

Could've been a bad head gasket,

88_rinker_v170

The junk boat sat out side for three years but the oil filter had milky oil as well So it was ran like that I'm assuming.the old head gasket was perfect and now that you said thermostat when I pulled the housing off there was not one in there. Could my block be cracked internally? If so how to I test that before I get carried away? 

88_rinker_v170

I just checked for a thermostat again and it's missing also the entire water jacket is all rust is that going to be an issue on a first start?

Black_Diamond

The water jacket will be rusty, normal. You need to pressure test the cooling system side to look for leaks. 

88_rinker_v170

What's the easiest way to pressure test it? Im an auto tech with limited marine knowledge

Black_Diamond

I'd hook up a good used car radiator and fill the block with water. Test just on a car from there. 

pault1216

I am no expert but I think the last line of your first post needs to be considered. A lot of work for an engine in that condition. If it was my boat and my family was on it, I would want something more reliable. I would go with a rebuilt marine engine close to the specs as possible of the original. Good luck!   -Paul

Black_Diamond

Good point with the above post. Dropping engine size may require a reduction ratio change in the outdrive and/or repropping too. 

88_rinker_v170

I have the matching outdrive for the engine I just want to check of the block is bad or not all the cylinders rockers push rods and crank had no rust or even a scratch on it of I have to wait for my 4.3 I will but I want to end summer  with my boat on the water.

youstolemybeer

take the block to a machine shop. they will coat it with metal dust and apply a magnet. IF they see a line of dust anywhere on the block that indicates the block is cracked.
Dont go down in size on the engine, you will regret it

88_rinker_v170

Well no cracked block and also found out it's a 3.0 not a 2.5 the milky oil was from no thermostat and sitting for years good compression across the board cleaned water jacket and treated with a rust inhibitor.thanks for your help guys