1976 Mercruiser 165 Engine Tick & Low Oil Pressure

[EZDuzIt]

I have a 1976 Apollo Tri Star 17' bow rider with the Mercruiser 165 straight six. At idle the oil pressure is right about nuts on 20 psi which seems a bit low to me. At cruising speed it's right about 40 psi. There is an intermittent engine tick which sounds like a valve/lifter tick. What baffles me is it comes and goes at all rpm's. Even at idle it comes and goes. Cold or full operating temp (140-150 degrees) it's very random. I've never had an engine tick be so random. Typically they're fairly consistent. The oil pressure at idle (600-700 rpm) is right at or just above the red zone (20 psi). Anything above idle and it comes up to right about 40 psi and stays there. The engine tick still comes and goes regardless of rpm or oil pressure. I believe I read somewhere that proper oil pressure is 30-55 psi so idle pressure is my only big concern. Before I take it in to a shop and pay $150/hr was hoping somebody could give me some pointers and advice. Cheers.

 

[Bondo]

Ayuh,.... 10 psi per 1,000 rpms is my rule of thumb,....

The motor is 40-odd years old,.... Go enjoy it,....

 

[Scott06]

Agree with bondo at that age and these were not the quietest engines new i wouldn’t go looking for too much trouble. I assume given age and the fact its still in one piece it didn’t get much use ?
if you are really dying to get into it or it gets worse would think it would be one of the following:
lifter valve hanging up or loose rocker- could take valve cover off and look it it
exhaust shutter ticking
exhaust manifold gasket but would think this would be constant

Not hearing it but if it were mine i would try - not sure what oil you are running i think these were specd for straight 30W
you could try heavier oil like 40 or 50 weight see if it disappears. Also if you look in valve cover and see a lot of deposits from lack of oil changes put some seafoam in crank case before next oil change let it idle 15-20 min. Ive seen it remove deposits may free up a sticky lifter

 

[itsathepete]

Agree with Scott06. Another option I have used with good results is the Motor Medic motor flush. Put it in and IDLE ONLY for 5 minutes then change oil. Use a heavier weight oil. The flush cleans a lot of junk out and the heavier weight oil will increase pressure on a worn engine.

 

[Lou C]

Other thing you can do is hook up a mechanical gauge to see if your dash gauge is accurate. On my old 4.3 (original short block, reman heads) I get 40 at cold idle, 40-60 when running and 20 after coming off plane hot slow idle. I think I’d check with a mechanical gauge & keep using it. Also use a straight 30, 40, 20/50 or the 25/40 that Merc sells.

 

[Scott06]

To OP what ever oil you use make sure it has enough zinc/ZDDP for flat tappet cams most modern oils do not...

I think rotella 15-W40 has enough with out getting into the hot rod type oil$

 

[matt167]

Rotella has not had a high zinc content in years. However it's good oil. I can't remember the brand but there is a cheap over the counter zddp additive that you can get at advance auto.. It night have been bars or risolene brand I don't remember it brings any oil up to at least 1,200 ppm which is where it should be

 

[Lou C]

You can also use Lucas Marine 20/50 it has a lot of zinc, more that just about any I’ve seen….

 

[EZDuzIt]

Thank you all for the pointers. I am running straight 30W as recommended. Other than the intermittent tapping it runs like a champ. I don't run it hard, rarely WOT. She's old and seems to have been well maintained before I got her last year. I've gone through just about everything so now the tapping is on my radar.

 

[Scott06]

Rotella has not had a high zinc content in years. However it's good oil. I can't remember the brand but there is a cheap over the counter zddp additive that you can get at advance auto.. It night have been bars or risolene brand I don't remember it brings any oil up to at least 1,200 ppm which is where it should be

True it is no longer the 3k ppm it used to be, but Its still about 1200 ppm which is enough for flat tappet cams. It is generally mentioned in a lot of threads as a cheaper alternative to more expensive classic car oriented oils.

 

[EZDuzIt]

Agree with bondo at that age and these were not the quietest engines new i wouldn’t go looking for too much trouble. I assume given age and the fact its still in one piece it didn’t get much use ?
if you are really dying to get into it or it gets worse would think it would be one of the following:
lifter valve hanging up or loose rocker- could take valve cover off and look it it
exhaust shutter ticking
exhaust manifold gasket but would think this would be constant

Not hearing it but if it were mine i would try - not sure what oil you are running i think these were specd for straight 30W
you could try heavier oil like 40 or 50 weight see if it disappears. Also if you look in valve cover and see a lot of deposits from lack of oil changes put some seafoam in crank case before next oil change let it idle 15-20 min. Ive seen it remove deposits may free up a sticky lifter

I'm a big fan of Seafoam. At the end of this season when I winterize it and change the oil, I was gonna run some Seafoam through it. I run Napa 30W oil but after reading the replies, much appreciated by the way, I'm going to go get a zinc additive. I didn't even think about that. It's definitely in the valve train and not an exhaust leak. It's not terribly concerning but I'm really anal about maintenance and my rigs running tip top. Especially with a boat. NOT something you want failing you potentially miles from the dock. Been there; done that. It's not a good time. I'm sure most of us who have spent a good amount of time on the water have been there at least once. Stuff happens and I do everything possible to prevent it. I've even considered going completely through the engine this off season. I'm slowly, but by bit restoring EZ Duz It.

 

[Scott06]

I'm a big fan of Seafoam. At the end of this season when I winterize it and change the oil, I was gonna run some Seafoam through it. I run Napa 30W oil but after reading the replies, much appreciated by the way, I'm going to go get a zinc additive. I didn't even think about that. It's definitely in the valve train and not an exhaust leak. It's not terribly concerning but I'm really anal about maintenance and my rigs running tip top. Especially with a boat. NOT something you want failing you potentially miles from the dock. Been there; done that. It's not a good time. I'm sure most of us who have spent a good amount of time on the water have been there at least once. Stuff happens and I do everything possible to prevent it. I've even considered going completely through the engine this off season. I'm slowly, but by bit restoring EZ Duz It.

Run a heavier oil and enjoy it dont rev it beyond 4200-4400 you will be fine

 

[EZDuzIt]

Run a heavier oil and enjoy it dont rev it beyond 4200-4400 you will be fine

Flat out WOT with just me, my wife and a full tank of fuel she turns 4500 rpm at 40 mph. I rarely open it up though. She cruises real nice at 3600 rpm and 30 mph give or take depending on load and burns about six gallons an hour.