1990 Johno 140hp V4 overheating at 3500 rpm

[ratbag's]

I have a mate having problems with his '90 Johno overheating when he goes over 3500 rpm.

Thermostat replaced.
Water pump replaced.
POP Valves replaced.
Heads removed, new gaskets.
Exhaust manfold removed, cleaned & new gaskets.

Still have the overheating problem after all this.

Model: 1990
HP: 140 V4

Any suggestions appreciated. Thanks, Ratbag

[therapy]

Mate, my only suggestion would be to post this question in the right section (boating chat) unless it's a stolen motor(or lost!!)

[Chris Ryan]

ratbag - A fellow Ausfish member had a similar problem as did I. My 1990 V4 115 overheating issue was a simple fix of using stainless steel strips to shorten the thermostat springs. Never had an issue after that.

[crabbie]

I had exactly the same problem with a 1996 130HP Johno after tangling with sand banks at night. Northside marine worked on it and gave everything a good flush and suggested that I take it for a good run. I did this but as soon as it reached 4000 rpm the alarm would go off, even though it ran fine at under 4000rpm.
Decided to flush it myself,fushed normally,flushed through thermostat inlets and outlets ,and backflushed any were and every were even used compressed air in conjunction! Had a bucket under the exhaust and keep getting a fine silt in the bucket ,only a teaspoon or less,must have done this for around 2 hrs. Finally took it for a run at under 4000rpm for about 10 mins then increased slowly to 5900rpm ,problem fixed.
Ask tour mate if he tangled with any sandbanks or very shallow water prior to this problem,if so the above may be the cure. I didn't accumulate a lot of silt from the motor but it must have been in the wrong place .
Crabbie

[cormorant]

Often the rubber gromet at the top of the waterpump or teh one higher up in the block get degraded and leak. Easy to test for if your mechanic has a clue using a water pressure guage. Seen lots of pumps installed incorrectle so worth a double check.

Have you done a compression check as a leaking head gaslet can do it as well

Have you checked the sensor to make sure it is reading corectly - use a infared thermometer