Too Low Op Temp in 4.3L V6 OMC/Merc Continues

[frank1492]

Update: This engine was checked by my mechanic and found to have a max operating temp at 3000 rpm of about 100-125 d as the gauge indicated.
Recall: New Mercruiser block, 4bbl OMC-supplied carb, mechanical fuel pump
I am still looking for more ideas on this. He is going to change the thermostat tomorrow on the assumption that it is defective/open, but I give that a very low chance of being at fault as he would have observed an open therm on installation and he is an excellent mechanic.
If it is not the therm there is only one other thing I can think of. The original OMC thermostat housing (replaces OMC 986292,987716,3850360) was replaced with a GLM 22600. He does not know if the interior was identical to the original OMC, but the GLM did come with a couple of plugs for unused ports. While I would doubt this is the issue, I can't think of anything else. What else would possibly cause the temp to be about 35 d. low?
Although I am past the 10 hr. break in period, I will not run this engine over 3000 rpm until the temp problem is solved.
Once again your help is much appreciated!
Frank

 

[Bondo]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

Ayuh,.... I believe the T-Stat is about the Only thing it Could be,....
But,.. Then again,...
I have No Idea what an OMC/ Mercruiser motor is supposed to be, muchless Look like....

 

[frank1492]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

Frank, are we talking oil temp or water temp? You got me a bit confused.

Either way, are you going by the dashboard temp guage? If so, don't. Check the engine with a thermal "gun".

He checked with the thermal gun which verifies the 125 d. reading, roughly the same as the gauge. The gauge always read about 160 with the old identical block, and you could always see the stat open if you observed the gauge closely.

 

[futz]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

saw this on the other site. same reply, your complaining about the motor running to cold?

The old block had alot of calcium buildup, rust buildup, and that makes it run hotter.

Once again there are alot of boaters that run no t-stat in their boat.

 

[Don S]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

Can you post some pictures of your engine and the plumbing. So we can see the hose routing etc.
Wasn't long ago a guy had an overheat or over cooling problem, and once he posted pictures, it was obvious the hoses were routed wrong.

 

[frank1492]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

The hoses are definitely not routed incorrectly. The new manifolds and thermostat cover are identical to the original ones, and I have been looking at those hoses and connections for the past ten years.
The tech at GLM said he has seen bad manifold castings, and although he said he never saw a bad t-housing, he said he wouldn't rule it out.
Thanks all so much for your ideas. I guess we should all wait until a new stat gets tried, which will be tomorrow or Wed. I will report back then.

 

[frank1492]

Re: Too Low Op Temp in 4.3L V6 OMC/Merc Continues

The stat has been replaced...temp checked with gun...same as before.
I have ordered an OEM OMC housing to replace the GLM aftermarket. Will report back. If that's not it, I have no clue.