7.4 running too hot?

[Baby Blue]

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

[ss3964spd]

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.

[mmwjr]

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.

[Baby Blue]

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

[Baby Blue]

Originally Posted by mmwjr

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

[mmwjr]

Originally Posted by Baby Blue

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.

[mmwjr]

Originally Posted by Baby Blue

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.

[mmwjr]

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.

[shrew]

Originally Posted by mmwjr

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.

[Baby Blue]

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.

[mmwjr]

Originally Posted by Baby Blue

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.

Then you'll still to get to the inner connection to install a block off plate.

[Baby Blue]

Does anyone have the backflush procedure?
Can't find it anywhere on the web.
Thanks. BB

[speedysprocket]

Can't see how such a procedure would exist or be possible. Everything in these engines is designed to flow only one way. You have two pumps forcing water through the engine and even if you hooked water up at the elbows, it's just going to go out the exhaust, not back into the engine.
Maybe instead you make a flush adapter and try something like salt away.

[mmwjr]

Originally Posted by Baby Blue

Does anyone have the backflush procedure?
Can't find it anywhere on the web.
Thanks. BB

IMO this is a waste of time for a boat raw water cooled engine. You can remove the hoses from the manifolds and flush water into them but you will need to bypass the raw water pump. this is done with the engine off.

This type of flushing is not going to remove marine growth nor rust scale.

[Baby Blue]

thanks for all the great info here. I'm going to return the circ pump and try another one. This started literally right after I replaced it. My thoughts where that a circ pump either works or leaks when failing.
I will posted the results along with IR exhaust temps.
thanks, BB

[Baby Blue]

I install another recirculating pump to rule it out.
Here's the temps I got ideling down the river. Lake Erie way too rough to get out and run it.

Gauge back where it's been the last two seasons 177ish.

IR temp readings
Thermostat housing 174

Starboard riser. 125
Port riser 144

At dock idling the port riser came down to 126.
I took these riser readings on the large metal tubes between the rubber boots of the exhaust.
Possible obstruction or rust etc on that riser?
Should I take the entire exhaust manifold off and try to clean it out?
Amy tips how to do this greatly appreciated.

[mmwjr]

Not the end of the world and should get you through this season without any issues.

How old is the exhaust? May just be time to replace it however I guess Lake Erie is not salty but you do have them damn zebra mussels.

[Baby Blue]

Yes. Fresh water. Zebra mussels a bit of a pain but not horrible.
I'm sure the exhaust is original so 1998.
Are they usually changed as the pair?
I'm assuming your referring to the exhaust manifold coming off the block and not the riser part right?
Thanks again for all your info. I really appreciate it.

Originally Posted by mmwjr

Not the end of the world and should get you through this season without any issues.

How old is the exhaust? May just be time to replace it however I guess Lake Erie is not salty but you do have them damn zebra mussels.

[mmwjr]

I am refering to both the riser and manifold.

Yes they typically are replaced as pairs.

[Baby Blue]

Thought I would post my results today as I think the temp problem is solved.
Our boat is a 1998 scr with a 7.4 mercruiser
Apparently our engine is a 1997.
1997 was the last year for carb for the 7.4.
I then found out that a carbed 7.4 requires a 143 degree thermostat and a mpi engine takes a 160 stat
I changed to a 143 stat and the temp never got over 170. Riser temps down also to around 120. This with 7 people on board. I think we are all good.
Thanks for everyone especially mmmjr for all the great info as always.
Have a great 4th of July!
BB