Question on 5.7L Chevy V8 compression

[nestorpr]

Hi guys! Well, I was finally able to check out my engine but first some background; this is a 1993 Volvo 570SP engine which is a 350 cid Chevy with 275hp. The first trip after I bought the boat I took her out for a short ride and the engine overheated, I'm not sure how long it was run in this condition but could have been anywhere from 1-5 minutes, no alarms went off and it was fortunate I looked at the gauge at that time. Turned off the engine and loud metallic clicks and clangs went off so I thought I must have cracked the heads. Towed back to shore and laid her up for a while. I finally took the time to check the compression out and found the following:

#1-170
#2-165
#3-165
#4-155
#5-135
#6-150
#7-170
#8-175

I was not able to warm up the engine first since I still don't know why it overheated and didn't want to aggravate the condition. However, the Volvo manual says the compression should be between 142-156 and these readings seem high, except for #5 of course.

So what do you guys think, did I crack the heads (I don't think so but am not an expert), did I blow a head gasket, is the engine salvageable without a rebuild? Whether I keep her or not will depend if the engine can be inexpensively repaired or not (will not rebuild it or spend more then $1000 for repairs). Thanks for any help!

[gofastsandman]

If you blow a gasket or crack a head it`ll blow white smoke. Maybe bent valves. Not a big job. Pull the heads and bring them to your fav. machine shop for a top job. Could also have dents in your pistons. More than 10 % differential on compression on any v8 is a red flag. Bottom line you need to pull the heads. Follow the bolt sequence and you`ll be fine.
GFS

[McGillicuddy]

I think if you blew a head gasket your oil would look like chocolate milk.

[Bushwacker]

You might want to do a leak-down test before pulling the head. That'll tell you if it's rings, valves or head gasket!

[gofastsandman]

You might want to do a leak-down test before pulling the head. That'll tell you if it's rings, valves or head gasket!

Sage advice as always! You can also shoot a little 30w oil in the cyl and do another comp. test. Spike indicates rings, but I was never invited to speak before NASA.
Nor will I be in the future.
I owe you some nooodles.
GFS

[seafari25]

Tough to kill those 350's. I understand when they tested those motors, they'd run for an hour or two without any oil or coolant before they'd crap out. I have one in an 82 shaggin wagon, all original, lotsa miles. I'm sure the compression isn't that great as she's been blowing blue ever since I've had it but I've put about 70000 miles on it in 9 years. I drove it to Florida about 3 years ago and she burnt about 4 litres of oil from Toronto to Daytona. Probably only had a litre in there when we reached.

As far as I'm concerned, those things are tanks. I do think they run better with oil though

[bitsamonkey]

I would fix the overheat problem and take it out again. After a long lay-up you can have stuck rings or rusty valves and valve seats that aren't seating properly. Both of these things can "fix themselves" by just using the boat. Just make sure you know why it overheated in the first place, fix that and then keep an eye on the coolant if freshwater cooled or look for excessive steam coming out of the exhaust. I doubt you damaged that motor by overheating it a little.

[Islandtrader]

Overheating is caused by lack of cooling.

Did you do a check on the raw water intake, and or change the thermostat? Start there and then see what happens.

[McGillicuddy]

A couple of other thoughts:

You might want to inspect the water jackets on the risers (elbows). If they are clogged (and this may kill more engines than we'll ever know) the exhaust will not cool and the engine will overheat - bent rods and all sorts of bad things happen.

It may also be that someone put the wrong oil in her. My GM small block used 30W. Once my partner changed the oil and used 10W-30 instead. Within a mile, it made a couple of terrible clangs and over heated. Needed thicker oil.

Finally the water pump could be going bad.

[nestorpr]

Thanks guys, I knew I would get some good advice here. I'm going to reseal the drive anyway so I'll rebuild the pump then (I already replaced the impeller on the engine) and will check the manifolds, that may have been the cause of the overheat since the previous owner did tell me that they needed replacing. I think you may be right, after such a long layup the rings or valves on #5 may be stuck, I'll run her and then do a thorough compression and leak check. Heck, I may be up and running by March, Thanks!