70hp vro -89 overheating

[Gabbu]

You should be using a 140F thermostat. 160F is considered overheating.

I ordered the 140F thermostat and that's what I have installed.

 

[Gabbu]

Tested the temp on top of the head. 160F, motor idled in neutral (barrel). Took her out for a spin, and engine sounded good. No overheat alarm. Didn't have a heat gun but engine temp (temp gauge) showed between 176 F and 194F.

When we measured the temp on top of the head =160F the temp gauge showed 176F.

 

[oldboat1]

Well, the issue seems somehow to be related to the t.stat - the device itself or installation. I don't recall if you tested it to see if it is operating correctly, but it's new.

If it were mine, I think I would run without the t.stat for a bit -- see what the operating temps are. If in a lower, safer range, test the t.stat, check installation instructions, and have at it again.

[Edit. Noticed I made a dumb mistake up in #6 -- water pump on the mind, but meant to refer to a bypass in the t.stat housing. Check and see if that is blocked at some point. Doesn't connect exactly with your symptoms, but worth checking.]

 

[Gabbu]

Well, the issue seems somehow to be related to the t.stat - the device itself or installation. I don't recall if you tested it to see if it is operating correctly, but it's new.

If it were mine, I think I would run without the t.stat for a bit -- see what the operating temps are. If in a lower, safer range, test the t.stat, check installation instructions, and have at it again.

[Edit. Noticed I made a dumb mistake up in #6 -- water pump on the mind, but meant to refer to a bypass in the t.stat housing. Check and see if that is blocked at some point. Doesn't connect exactly with your symptoms, but worth checking.]

Is the bypass located in the head or behind it? I have tried to look but can't figure out where it is.

Testrun #4 in sea. Cruising speed 4000rpm highest readings 187F, Idling 176F, WOT 167F.

There is a 20C temp disparity between the readings on the block (temp sender) and the temp on the thermostat housing.

 

[oldboat1]

Try backlashing the head from the bottom. Should exit in the thermostat housing at the top.

 

[oldboat1]

[...that's backflushing.] auto-correct....

I would try another IR gun and compare IR readings, just to be sure. Dash gauge is suspect (high) -- may be a sender issue.

 

[Gabbu]

[...that's backflushing.] auto-correct....

I would try another IR gun and compare IR readings, just to be sure. Dash gauge is suspect (high) -- may be a sender issue.

I have cleaned the head in my ultrasonic cleaner, three 30 min cycles in 149F, added some cleaner I don't know the name of. I noticed some salt debris that was tough to get rid off. But I consider the cooling passages inside the head quite clean.

Did some new tests, ran the engine in a barrel. The temp on the head was 140F, while the temp sender showed 176F.

 

[oldboat1]

Sounds good. Maybe time for a new gauge and sender.