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Old 01-29-2014, 07:08 PM   #1
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Temps: 1977 Mercruiser 350 cid / 255 hp

Getten Our Tolly Gal ready for spring, summer, fall 2014! So far all points seem a Big GO!

Couple days ago at dock I was doing various levels of engine temp checks with IR gun. Thought it good if I'd ask thems w/ 350 gassers for their findings/input...

Heat Exchanger FWC, 1977 Mercruiser 350 cid / 255 hp; Real Good Cond & Fully Warmed:

What temp range do you feel the risers and manifolds should be... when?

1. 1000 rpm in neutral

2. 1500 rpm in gear

3. 2500 rpm in neutral

Thanks in advance!

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Old 01-29-2014, 08:46 PM   #2
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I'd be interested in hearing those numbers too. I'm to lazy to check. My engine fires up, step to the stern and visually verify water in exhaust, put in gear and enjoy the trip.
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Old 01-29-2014, 09:01 PM   #3
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Li am going back 15 years so maybe getting confused with another boat I've owned.

I don't have exact temps but I do remember feeling them for temps. At idle mine were cool to the touch, after a hard run they would be hot to the touch. Not burning you, but hot. I was told that consistency between the two sides is more important than being a few degrees higher or lower, as intake water temperature plays a role too.

I assume you have twins so id check for consistency between all 4 risers.
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Old 01-29-2014, 10:16 PM   #4
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Quote:
Originally Posted by eseyoung View Post
Li am going back 15 years so maybe getting confused with another boat I've owned.

I don't have exact temps but I do remember feeling them for temps. At idle mine were cool to the touch, after a hard run they would be hot to the touch. Not burning you, but hot. I was told that consistency between the two sides is more important than being a few degrees higher or lower, as intake water temperature plays a role too.

I assume you have twins so id check for consistency between all 4 risers.
On both engines I checked visual water flow out exhaust at each rpm level; increased as expected. I also played the hand test on manifolds and risers and did IR readings not only on exhaust manifolds and risers, but also... on intake manifold, valve covers, exhaust tubes past engines, fresh water tank and raw water tank on heat exchangers as well as at thermostat casings.

Reason I'd like to learn others results for the temp ranges per rpm in or out of gear I mention in post # 1... is because... I can't locate accountable source for number averages on the web. That said, I'm not confident that all my IR readings were correct, in that, I found it difficult to keep the gun exact distance and/or angle from all areas. I spent quite a while in the engine compartment testing over and over again... so I feel I have a pretty good average in mind for each rpm level. Naturally as rpm increased so did exhaust manifold temp increase. I have no idea what temps would be created at some 3200 to 3600 rpm while quick cruising or at WOT - but, I'd like to learn that too if anyone might know! I often cruise efficiently just below hull speed at reasonably low rpm. Scenery... I love scenery!

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Old 01-31-2014, 10:50 AM   #5
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On previous boat with small block Chevy (sbc) after they were well warmed up 90f to 94f if I remember right at 1000 to 1200 revolutions per minute (rpm). These were 225 horse power (hp) Volvo marinization units, other brands may be different. Mine were freshwater cooled don't know if there would be any difference in raw water cooled.
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Old 01-31-2014, 11:11 AM   #6
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On previous boat with small block Chevy (sbc) after they were well warmed up 90f to 94f if I remember right at 1000 to 1200 revolutions per minute (rpm). These were 225 horse power (hp) Volvo marinization units, other brands may be different. Mine were freshwater cooled don't know if there would be any difference in raw water cooled.
Ron - You refering to risers or manifolds? Manifold I imagine at 1000/1200 rpm in neutral??
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Old 01-31-2014, 11:55 AM   #7
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[QUOTE="Art;209762"] Ron - You refering to risers or manifolds? Manifold I imagine at 1000/1200 rpm in neutral??[/QUOTE

Risers & elbows while running in gear at 1000 to 1200 rpm, I'am sure I also checked the manifold, heads & thermostat housing. The heads on one engine ran @135f the other engine the heads ran @157, the difference was someone had installed a raw water thermostat 140f in the cooler one. I'am pretty sure the riser & elbow temp may of ran higher at higher rpm but I always ran about 1200 rpm, I checked several times over the years & 94f is the highest temp I ever remember on the risers & elbows. My Hino diesels on our 3870 the elbows & risers run in the mid 60f while cruising.
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Old 01-31-2014, 12:10 PM   #8
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[QUOTE=River Cruiser;209780]
Quote:
Originally Posted by Art View Post
Ron - You refering to risers or manifolds? Manifold I imagine at 1000/1200 rpm in neutral??[/QUOTE

Risers & elbows while running in gear at 1000 to 1200 rpm, I'am sure I also checked the manifold, heads & thermostat housing. The heads on one engine ran @135f the other engine the heads ran @157, the difference was someone had installed a raw water thermostat 140f in the cooler one. I'am pretty sure the riser & elbow temp may of ran higher at higher rpm but I always ran about 1200 rpm, I checked several times over the years & 94f is the highest temp I ever remember on the risers & elbows. My Hino diesels on our 3870 the elbows & risers run in the mid 60f while cruising.
TY for clarity Ron. Now I understand, i.e. "Risers & elbows while running in gear..." Those numbers seem to correspond pretty well to what I found on my twins while IR Gun checking temps the other day.
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