Volvo Penta 4.3 (rebuilt with Chevy Vortec v6) overheat and lack of power

[chuongnino]

Hello. Thank you for your help in advance. I am a complete newbie so please pardon my lack of knowledge.

A little background: I recently bought a 1999 Larson boat that has a rebuilt V6 Vortec engine (originally 4.3 Volvo Penta) with a Volvo Penta Cobra outdrive. After the first outing, I have noticed several issues:

1. Engine is lack of power. At WOT I do not see it goes above 2500 rpm. I did check the spark plugs and they all looked bad. I replaced all 6 plugs but have not taken the boat out. Where else should I check for this problem beside the spark plugs?

2. Engine is overheating. The thermostat is not working so I could not tell what temperature it was operating at; but for sure over 200F. I suspect it is a water pump problem so I took the raw water pump apart to inspect. The impeller looks torn to me. Can you please tell me if the impeller and/or the pump are bad? I attached a photo for your reference.

3. After 1 hour of running around the lake, I noticed there was a decent amount of oil in the bilge area. When I run the engine on the muff, I do not see any leaking oil. Where should I check first for this problem?


Further inspection tells me that the exhaust bellow is torn. I ordered a new kit to replace both bellows and gimbals bearing.

 

[Scott Danforth]

First, you severely overheated the motor. Riding around for an hour with the motor overheating probably killed the motor. That is where the oil came from

with any new to you boat, you have to do every bit of maintenance, and assume the prior owner didnt do any of it.

That includes raw water pump service, complete drive service, alignment, new bellows, inspect tge gimbal. Engine to have fuel system serviced, all filters and fluids, and new plugs

Then move on to the trailer

The moment it overheated, you should have keyed off and got a tow

Start troubleshooting. Start with a compression test. You should have between 140 and 150 psi in every cylinder. This is to assess how bad the motor was overheated

 

[chuongnino]

Thank you! I was stupid but did not really run it for 1 hour. Maybe 20 minutes, soon as I figured it overheated I quickly put it back on the trailer and went home. I did the compression test (before and after) and all cylinders are in the 135-150 psi range. Also did spark plug jump test and all plugs are jumping the 7/16 gap fine. My next task is to replace the bellows and gimbal bearing. I will check the fuel tank and line as well.

Does that raw water pump impeller looks fine to you? I replaced a couple outboard impellers before and they don’t look to be sitting pressed that tightly at the top of the pump. My main concern with the pump is whether a wrong impeller was install or the pump itself is bad?

 

[dypcdiver]

Your raw water pump should not have been put together with a sealant. Buy a new impeller from Volvo Penta which will come complete with a gasket. The impeller you have looks as if it has not been pulling any water and overheated. Once installed you must make sure that it is pulling raw water from the outdrive, by testing you have water flow at the 2 elbows on the forward ends of the manifolds that are supplied by 2 hoses from the thermostat housing.

 

[alldodge]

Does that raw water pump impeller looks fine to you?

No, the impeller has separated from the center

 

[chuongnino]

Thank you very much for your inputs!. I will replace it and report back. Hopefully that will solve the problem.

 

[Scott Danforth]

dont forget to check your exhaust coupling hoses. running without water, they are probably burned up on the inside.

 

[chuongnino]

Thank you Mr. Danforth, I will make sure I check for that.

A quick update, I was trying to find the missing pieces of the old impeller by hooking a garden hose to water outlet on the water pump to flush the system (please correct me if I am doing it the wrong way). With most of the hoses off, the thermostat housing looks terribly corroded to me. Should I replace it? Please see picture.

 

[Scott Danforth]

wire brush it, paint with a good primer and paint, then find the other bits your missing.

or if your a bit lazier, soak it for a week in oxalic acid, then neutralize, and then prime/paint.