Sm. motor - no thermostat - possibly overheating - isolation of fault? (E3RCUA)

[Good Trout To You Sir]

Motor: 1987 Evinrude 2.5HP (E3RCUA). Model design lacks thermostat. Tell-tale in form of spray generated through 8 small holes on midsection (4&4).
History: Motor abused by previous owner. Plastic wire insulation showed signs of heat stress (melt) when I acquired motor. Since my rehab with new fuel pump, carb clean, new water pump assembly, I have 80+ hours on motor. Generally runs well, though I have lower unit bearings, seal issues to address.
Symptoms: Motor possibly overheating when throttle advanced past 1/3 speed. Because of water churn, nearly impossible to observe tell-tale spray under operating conditions. Spray is visible when running in test tank. Underside of midsection flange - where bolts to block - strikes me as hotter than acceptable when running 1/3 speed or higher. Too hot to maintain hand contact. When motor slows to 1/3 throttle or less, this same location cools very quickly......within 10-15 seconds it's no more than slightly warm.
Cowling is a dreadful design. Not at all easy to remove. Impractical to run motor without cowling on the water. With no thermostat in design, no way to observe tell-tale spray on the water and no temp gun in my tool kit, what is litmus test for yes/no on overheating and the pathway for troubleshooting assuming impeller is not at fault?

 

[Joe Reeves]

Without actually being there to observe... rather then to assume, if it were me, I would dismantle the water pump for inspection, make sure the impeller has not taken a curved set... and seal the pump upon re assembly with Bombardier 3M Product #847 which may be listed as Scotchgrip 847, part number 776964.

A 2nd thought is that the engine is too high on the transom or auxiliary mount... at a fair height at low speed to draw water BUT too high in the water at a higher speed, causing the unit to draw air.

 

[Good Trout To You Sir]

... seal the pump upon re assembly with Bombardier 3M Product #847.

Joe - Thanks for your interest in advising.
Complete pump assembly replaced 10 months ago: flat gasket, wear plate, impeller & key, housing and ring-type gasket to seal housing to wear plate. Upon inspection, I plan to replace impeller and key, even if impeller appears OK. Under "normal" circumstances OK to reuse all other elements of water pump assembly?
Do not recall applying liquid sealant to mating surfaces of wear plate to housing since ring-type gasket was present. You would use liquid sealant on those surfaces as well? (I didn't on account of concern seal created by ring might be compromised by liquid sealant applied around & on top of it.)
Thanks again.

 

[Joe Reeves]

As long as the "O" Ring seal's seat (top & bottom) is not corroded... just giving it a coating of grease should be sufficient

My view on reusing parts is simply... if it looks as good as new, use it.

 

[Good Trout To You Sir]

OK. Flat lip between gasket channel and housing exterior is quite slender.....at least on a 2.5HP it is!
Do you use #847 in that area in order to seal the pump upon reassembly? Thanks.

 

[Joe Reeves]

On gaskets, I use regular Gasket Sealer... comes in a can with a brush attached to its screw off cap.

On metal to metal, metal to plastic, & "O" Rings, I use the 847..... There are exceptions... see the following:

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(Gasket Sealers)
(Usually available at any reliable automotive parts type store)
(J. Reeves)

Do Not use any type of sealer on outboard carburetor or intake manifold gaskets as this would cause blockage of various fuel/air passageways. Also, there are new type gaskets, including head gaskets, which are used through out the engines that are coated with a substance that gives a shinny appearance to them. These gaskets are coated with a self sealer and are to be installed as is.... no sealers! Older style head and fuel related gaskets that are not coated with this substance are to be simply coated with oil.... nothing else.

All other gaskets (hopefully I've not overlooked anything above) should be coated with Gasket Sealer (the type that comes in a can that has a small brush in its screw off cap). This also pertains to some water pump installations that use a gasket between the plate and the lower unit housing.

Marprox Sealer 1000 or OMC Adhesive or Boat Armor Sealer 1000 (same substance)[See Below Note] should be used on any metal to metal (Unless GelSeal Is Called For) or metal to plastic surface (such as impeller hsg to plate, and plate to lower unit surface) to eliminate air leaks. It should also be used on the Spaghetti tubing that is used on many powerhead crankcase halves, lower unit skegs, etc. I have found that this substance works quite well on various "O" Rings such as what are found on lower unit carrier and upper driveshaft bearing housings (Note that this substance is obviously not to be used on all "O" Rings). This substance also works quite well in sealing the surfaces between the lower unit and the exhaust housing to which it attaches, eliminating the unsightly water spray between the two after completing a water pump installation.

NOTE 1: I am under the impression that Marprox Sealer 1000 and Boat Armor Sealer 1000 is no longer available.

NOTE 2: OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964

DO NOT use any sealer on the large "O" Rings that are used on the upper and lower crankcase heads (The housing/heads that slide over the top and bottom of the crankshaft). On those "O" Rings, use only a coating of grease.

The exception of surface to surface contacts pertains to the later model matching crankcase (block) halves (which does not incorporate spaghetti tubing) which call for "Gel-Seal", or any other surface that calls for Gel-Seal. This substance seals in the absence of air, and if called for, must be used. One other form of Gel Seal that can be substituted is "Loc-Tite #518". Nothing else that I know of will do!

I advise against using silicone or permatex (the heavuy black substance in a tube) on a outboard engine. It simply will not function properly. The exception to this (as per OMC's recommendation), is to use the black Permatex (heavily) on the gasket 306242 which separates the inner exhaust tube from the exhaust housing on the 1959 35hp and 1960 to 1970 40hp OMC outboards.

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[Good Trout To You Sir]

Much obliged for the detail re: sealant. Your 2nd idea re: overheat cause has me thinking. Two follow-up questions:
Transom height: What is minimum submersion depth necessary for proper water pump operation....perhaps as measured from water intake ports to water surface?
Second question results from observation of pump intake port positioning on this model. Notice in my picture how the intake ports (1 of 2 shown) are NOT positioned on the side of the lower leg shaft, but rather on the underside of the housing that joins the lower unit to the midsection. Seems to me most of the water flow would run parallel to the screen instead of directly into it. Is this a design flaw that would reduce the flow of water into the pump? If so, is there any way to mitigate (screen removal, etc.?)