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Old 06-27-2016, 08:22 PM   #1
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Default 7.4 running too hot?

1998 SCR
7.4 mercruiser carbed
bravo 3 drive
3rd season with the boat

since we've owned the boat it's normal operating temp has always been around 180 degrees.
last off season I did all the bellows and maintenance items along with impeller.
first couple times out still ran at 180, colder water though mid May Lake Erie off Cleveland (go cavs baby!!)
anyway... this season the circulation pump went out so I replaced that and ever since it seems to run slightly hotter. I'd guess around 185-190.
Tough to find a clear answer on normal operating temp.
I just put a new 160 degree state in it this week and same results.
I have put my hand on the exhaust pipe exiting the boat and hold it there for about 3 seconds before it's too hot.
I ordered an IR temp gun to check those temps but hasn't come in yet.
Temp guage was new 2 years ago.
questions are:
1. does this temp seem too hot? if so what are some operating temps from members with similar set up?
2. I was thinking about backflushing the unit but can't find any procedures on that process. Done this on cars many times but never and boat.
any info and advise appreciated.
thanks, BB
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Old 06-27-2016, 08:59 PM   #2
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From what I've read 180 is hotter than most carb'd boat engines run. The FI 350 in ours runs just a bit over 175.

If it was running at 180, and the only thing you changed was the circ pump, and now it's at 185-190, the new pump certainly seems to be in question. Could be the impellor in the pump was pressed too far onto the shaft, or not far enough. You might consider pulling the rear cover off of both to compare.
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Old 06-27-2016, 11:06 PM   #3
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Open system? If yes 180 is too hot. When you have the IR sensor start with the t-stat then the exhaust and report you readings.
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Old 06-28-2016, 01:32 AM   #4
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Default 7.4

Yes it's a raw water open cooled system
One thing to add
After I installed the circulation pump and first started it a few seconds after starting it the bearing was whining pretty good until water got to the pump and then stopped and hasn't returned since.
Not sure if that's normal or not.
Again this is the circulation pump I'm referring to and not the impeller.
Thanks!
BB
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Old 06-28-2016, 01:41 AM   #5
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Open system? If yes 180 is too hot. When you have the IR sensor start with the t-stat then the exhaust and report you readings.
Mmwjr
What temp readings should I have there?
Once I get the temp gun I'll do that ASAP and post the results.
Thanks!
BB
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Old 06-28-2016, 03:49 AM   #6
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Quote:
Originally Posted by Baby Blue View Post
Yes it's a raw water open cooled system
One thing to add
After I installed the circulation pump and first started it a few seconds after starting it the bearing was whining pretty good until water got to the pump and then stopped and hasn't returned since.
Not sure if that's normal or not.
Again this is the circulation pump I'm referring to and not the impeller.
Thanks!
BB
The bearing should not see water as a seal should keep it dry. Water would destroy the bearing. May have a bad ball in the bearing and after a few turns wore off the imperfection.
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Old 06-28-2016, 03:51 AM   #7
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Quote:
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Mmwjr
What temp readings should I have there?
Once I get the temp gun I'll do that ASAP and post the results.
Thanks!
BB
T-stat housing should be at what the t-stat installed, 140 or 160 F.

Exhaust should be about 120 F.
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Old 06-28-2016, 03:56 AM   #8
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When you did the bellows did you replace the water hose as well. Bravo water hose on the transom assemblies are know to clog over time as instead of a barbed fitting and hose clamp it uses a plastic insert to retain the hose.

If the boat is wet slipped this may be your issue as it stares the raw water pump.
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Old 06-28-2016, 01:45 PM   #9
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When you did the bellows did you replace the water hose as well. Bravo water hose on the transom assemblies are know to clog over time as instead of a barbed fitting and hose clamp it uses a plastic insert to retain the hose.

If the boat is wet slipped this may be your issue as it stares the raw water pump.

I'll second that. I am in the process of replacing my transom assembly (1997).
The aluminum around the intake hose in the transom assembly 'corrodes' for a lack of a better term. It crushes the hose and restricts water intake. We estimate mine had approx. 40% constriction. It caused my temps to run hot as well.

I'd also make sure the manifolds and risers aren't causing an issue. They get replaced on average every 5-8 years in saltwater.

Your temps seem too hot for me. I was around 185 -190 and that is what alerted me to a problem.
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Old 06-28-2016, 05:31 PM   #10
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I will check the risers but in freshwater.
We did not change the water inlet hose on the transom assembly. seems just about impossible to get to inside the boat and it looked good.
I'm considering changing it to a through hull fitting rather then picking up water from the bottom of the outdrive.
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