Engine Temp Fluctuation

"2000 Maxum 3300 SCR T-5.7L B-

"2000 Maxum 3300 SCR T-5.7L B-2

Engines, manifolds, risers, elbows all new spring 2007

I Launched on saturday, all good, but when i planed out,i noticed port motorclimb to 210 deg.
I backed out of throttle, temp dropped to 165. I watched it closely and replanned, again it would run at 170 then climb rapidly to 190-220 and fall quickly back to 165 170.

I returned to the marina andran it in the slip. at 2500-3000 rpm,it would warm to 170 then it would spike to 190/210 and quickly fall to 170.

Manifolds and elbows feel COLD, T-stat housing is cold. intake manifold is warm/hot under the t-stat housing.

I replaced t-stat, still same.

I replaced the water pump, thinking i had a wiped impeller, (Old one was fine) Symptoms still same.

I took the boat out again,and the same symptoms ..... seems to run at 170 but the guage spikes to 190/210 and quickly returns to 170-175

I removed the water hose (raw water to t-stat housing) and have a full flow of water into a boucket.


Both engines have always run at 175 deg showing on guage. ALWAYS.....

Is it possible a bad sender or guage??

Tom"

"Definitely possible. Run a t

"Definitely possible. Run a test --
Swap first the temp senders for both drives and note whether problem follows the change, indicating a bad sender. If not, next reverse the wiring leads to the guages (remembering which is which as you moniter the temp at the dashboard) again seeing whether the problem follows this swap. If the same guage always shows the fault it is the guage.

In either case, replace the guity component and go again (swapping the wiring back to normal). If these swaps do not indicate signal/guage problem error, then you know you have a real problem to track down.

Have you checked flow from the engine mounted circulating pump? This unit could be failing. Does the exhaust line have a shutter that could be restricting outflow?"

"A 5.7 should pump about 5 GPM

"A 5.7 should pump about 5 GPM of water at 1000 RPM.

Here is a list of the usual overheating suspects, just for reference:
-pump impeller and/or housing bad; insufficient water flow
-leaking water pump to water pipe coupler; coupler not fully sealed
-foreign object in inlet hose or T’stat housing (such as impeller pieces)
-kinked hose between drive leg and transom assembly
-collapsed, blocked or kinked hose, blocked PS or oil cooler, etc
-T'stat stuck, partially plugged, or missing
-bad circulation pump or belt
-plugged exhaust manifolds or risers
-plugged check balls in T fitting lines to risers (where equipped)
-salt and/or corrosion encrustation or other blockage in block, heads, manifolds, risers, hoses, or heat exchanger (if equipped)
-bad exhaust flapper causing higher pressure in one riser than the other, and causing discharge water to preferentially flow to the other riser.

Rod"

"I am going w/Rod's list &

"I am going w/Rod's list "T'stat stuck, partially plugged". Mine did that the first time out this year; probably rust particles. It stopped after a few minutes of the T'stat operating."

"Tom,
Sounds like we need t

"Tom,
Sounds like we need to take Guy's advice and run it around a few minutes to give it another chance to come up to proper temp while I shoot it with the infra-red temp gun to verify the sender and gauge.Not a bad idea to have another thermostat handy too.....Todd"