Low oil pressure high temperature on OMC Stern drive with 5.7 liter Chevy 350

[stancalame]

Friends, Romans, Countrymen, PLEASE lend me your ear.

I have a 1992 Galaxie 20' runabout I/O with OMC King Cobra sterndrive and 5.7 Chevy 350 engine. Engine is rebuit and not sure how old it is as I bought boat used. I had the motor pulled out last year to replace a piston that looked like it burned too lean from the color on the valves compared to others. I have a very knowledgable (older neighbor who did the work so I did not witness the replacement. He's rebuilt hundreds of motors so I trust him. After that, I I discovered rear main leak so had to pull it again and fixed it. I think my neighbor may have pinched the seal installing. He's very experienced but does not see well these days.:confusion:

After replacing main seal, boat ran well remainder of last summer. No temp or oil pressure issues. I took boat out today after replacing prop with same Aluminum 14.5" X 19 pitch prop that came off of the drive. Old prop had damage on all three bladeshowever but still ran pretty good howvever; I had noticed vibration at lower speeds and same experienced neighbor indicated vibration could damaged shat seals. I have never been into the lower unit and owned boat for two years. I know I need to service with lube and now thinking I need to check impeller.

So my current issue is that my daughter and I drove it for a good 20-30 minutes at 40-40MPH, 3,500 to 4000 RPM. I let my douaghter drive so I could check out the newly recovered back bench seat, when I started smelling smoke. I immeadiately had her shut it down and I checked under cowling and did not check the guages. Engine seemd really hot but no visible oil anywhere.I pulled dipstick and oil was below ADD line however it creeped up the longer I waited.

I tried to restert but engine would barely turn over and I stopped. I've experienced that beofre when engine hot. I waited another 5 minutes and engine started and I observed oil pressure at 20 pis when its normally a strong 60. The temp guage was at least 215 but I didnt let it run long. I got a tow back to ramp and mannually trailered boat. When I got it back home, I put muffs on it and started again. It turned over stronger and took a few more revolutions to start but it did. My Oil pressure came back to 60 psi but temp was high 200F+ immeadiately.

Im not sure what where to go from here but sure that I cant take it out until I understand whats happening.

1) My first thought hot temp was that maybe thermostat was not cooling but seems I would have had higher temp sooner than 30 minutes but maybe not.
2) Second thought is maybe water pump shot and not pumping enough water. Maybe new prop was grabbing more water putting more strain on motor, buy why would oil pressure drop if it was water pump impeller? Does not seem logical.
3) Weak oil pump gave up buy is this discription indiciative of that especially since presssure came back up after it sat for 30 minutes while I transmported on trailer home.
4) Have I screwed something up in the engine? I hope not, I'd hate to have to pull it a 3rd time in 18 months.

Whatwould you do? I can do minor checks but am not that knowlageable on innerworking of engines. I'll be consulting my mechanic neighbor but thought I'd get a head start tonight.

I'm sure I've left pertinent iformation out so let me know your thoughts.

 

[southkogs]

Sounds to me like ya' overheated ... my first suspect is the impeller. I would change the impeller. Do an oil change (check for water in your oil), and check your stern drive lubes (if you haven't - change them).

Then try it on muffs and see if it holds temp and idles right.

 

[Lou C]

Yep you can start with the impeller which on a Cobra is very easy to do. Just make sure you get that oring seal in right and if you are missing pieces of the old one, back flush the hose from the thermo housing to the transom mount with the impeller housing off, to flush out the old pieces of impeller that might be in the P/S cooler on the back of the engine.

 

[stancalame]

Awesome guys, I was sweating it when the site went down. You've comfirmed what I was thinking. Does it makes sense that oil pressure dropped when over heated? That threw me. I've had slow starting when hot in the past.

Just thinking ahead here assqeual I tend to do (worry wart), what is symptom of weak or eminent failure of engine water pump. I assume it would start sqealing but any other tale tale signs.

 

[stancalame]

No Title

Another question: How do I search for the correct partnumbers for replacement parts for stern Drive and Engine? I have posted pics below. I would think Stern Drive would be easy since I hav e model and serieal but I've searched before and never see my model code. It is s King Cobra.

The motor is a "crate engine" that was installed a couple years back back previous owner. Its a chevy 350 but I dont know how to identify anything specific. There are some numbers cast into the intake. Would that help. Just wondering for future needs for parts.

 

[Scott Danforth]

You severely overheated the motor, that is why your oil pressure was so low and the motor was hard to start

 

[stancalame]

I see. I guess no real way to tell if damage is done other than look for water in engine oil and leaks for water and oil in the engine compartment?

 

[Scott Danforth]

keep a close eye on it. especially the gauges. there is a temp gauge on the boat. anything over 160 in a raw-water cooled motor should be considered high.

 

[Lou C]

The model # for most OMC Cobra engines will start with whatever the displacement of the engine is (1st 2 digits) followed by a 2 or a 4 denoting a 2 or 4bbl carb, then there will be a P (power steering) or an M (manual steering) followed by a group of letters. That tag looks like it was on the drive, the one you use to order engine parts is usually a sticker on the thermo housing or on one of the valve covers.

http://www.crowleymarine.com/1/OMC-Stern-Drive/1992.cfm

 

[stancalame]

Thanks Scott for the temperature guideline. If it should be at 160 then I'm a little nervous, I thought 180-200 was ok. Thats where its been runningm when I used it last season. I'll check my oil and gear lube.

Lou C, THanks for the model number run down. I talked later this afternoon to a guy at a narine parts store and he indicated the same. I pretty sure I've looked on the motor for tags and have never seen any. Its not original motor and the only thing I know about it is that it its a chevy 350. I'm starting to realize that there are specialized marine parts for the engine that differentiate it from a car engine, like manifolds, water pump and others.

Looks like there are three 5/7 L engines, all with 4BBL Carbs, and PS, al of which mine have. Any particular components that could help me distinguish mine as one of the three? I suppose I could go through the components and compare...

I guess my best best is in future when I need enginer parts, I'll just need to take with me to auto parts store or take a pic and post it on this forum. Thanks for help. I'll post what I find, Im headed bak to check it again tomorrow.

 

[Scott Danforth]

Raw water only cooled motors have either a 140 or 160 degree thermostat. Unless you have a bad raw water pump, or your cooling system is plugged, that is where the temp should be.

I suggest you do the following:
Replace the raw water impeller/pump. If any pieces are missing - find them
Back flush the cooling system, especially the power steeting cooler
Pull the hoses and back flush them
Pull the manifolds and risers, inspect the water jacket for rust clogging

 

[stancalame]

Got it, I wish I'd inspected whe last time I pulled the motor. When pulling manifolds, will I need to have new gaskets? I'm trying to get boat functional for family gathering next week and would need to order them.

I plan to pull impeller today and will back flush every thing. Any tricks of the trade on back flush. I assume I just insert garden hose with hose clamp maybe and turn on the water?

A little off topic but since Im here, want to check/replace lower unit gear oil but out drive will not extend in full down position due to ground clearance. Is it mandatory to get lower unit all the way down in order to get all the old fluid out?

 

[southkogs]

Is it mandatory to get lower unit all the way down in order to get all the old fluid out?

Hasn't been for my Merc. "Mostly" down has done the trick.

 

[stancalame]

I tried loading the pics I took but ket getting "Error uploading picture" Not sure why becuase all pics are less thgan 110 KB. I found rubber supply tube to pump brittle and disconected, impeller had three blades missing. I back flusher and found them all. Hope to get it back together tomorrow. Drained engine oil (black) and lower unit oil and found no emulsion so I think I surevived the over-heat epesone with no damage. Whew!

Thakls for the help. Next up, erratic trim guage and, and sticky steering. But thas will be another day and another paycheck.

 

[stancalame]

No Title

Logged out and back in, now pics loaded.

 

[Lou C]

Here's what you need....you have the Cone Clutch Drive, not the standard Dog Clutch Cobra....

http://www.crowleymarine.com/johnson...arts/56252.cfm

As far as flushing, I like to do it 2 ways:

with the impeller housing off...
1) hook up your muffs to the lower unit, then hold the muffs tight to the drive while someone turns on the water, you should see water spurt out of one of the openings in the impeller mount.
2) OK now go up to the front of the engine, then disconnect the hose that goes from the transom mount to the thermo housing, at the thermo housing. Then stick your garden hose in it and turn it on, while someone watches for water out of the other opening in the impeller mount. IF you get good flow from both of these, then its probably fine.