2005 FV 312 Temp Guage climbs to 225

[allaboutus]

This is a problem for all the arm-chair mechanics out there.  A while back I wrote in about a potential problem I was experiencing.  Here is the problem.  At idle speed and low RPM's, my temp guage indicates 175.  As I increase the RPM's and get on plane, after about 15 minutes of cruising, the temp guage slowly increases to 225.  It stays at the top of the guage for approximately 30 seconds, then the engine sputters, and it drops back to 175.  The alarm does not sound.

I had multiple mechanics look at it.  They replaced the thermostat (actually went through two of them) and impellar.  The most recent mechanic compared the flow to the other engine and it looked good.  He also took a reading of the thermostat unit and found that the bottom of the unit was 225 degrees yet the top of the unit was 175 degrees.  That is why the alarm does not go off since the sensor is on the top part of the unit.  The mechanic then proceeded to rule out flow, water pump and everything else he can think of.  

The fact that it only happens at 3000 - 4000 RPM's and that it does not happen all the time is what is perplexing him.  We cruised around for about 25 minutes and it happened twice during that period and never when travelling at less than 2000 RPM's.  It never stays at the high 225 degrees temp and always drops down after 30 seconds.

So, next on his list is to replace the gasket (which he does not think will do anything).  He looked at the out drive and there is nothing blocking it and he said that if there is a problem down there, it would happen all the time and not intermittently.  Prior to pulling the boat out of the water, he is going to replace the hose with a clear hose to see how the flow from the out drive is.  But he said if that was the problem, it would be happening immediately upon planing and not 10 minutes later.

The boat is a 2005 FV 312 with dual 270 Volvo Penta 5.0 GXI-E with 180 hours.  Does anyone have any suggestions?

[Dream 'Inn]

hmmm...sounds like a hard one  to figure out.  Maybe possibly something in one of the many hoses.  Or possibly a combination of a couple things.  Good luck and let us know the outcome.

[Black and Tan]

Very Strange. i am assuming that the engines are salt water cooled, so if you ran through some shallow water it could be that the blocks have some sand in them but normally you would see a restrition in flow but not always. Also it could be a hose collapsing internally normally the water inlet hoses because they are under suction. Your nomenclature doesnt mention any of the Ocean Series drives but if you do have them the water inlet hose can be pinched between the U-joint bellows and exhaust ports when you trim, but if you have the DP drives there is no issue there. Keep me posted im interested.

[Mikes342]

I had a similar problem with a volvo engine on a 99 Four Winns with a 280 hp engine.  A mechanic put a clear hose on the water input hose and saw a bunch of bubbles at higher RPMs.  This was caused because of air leak where the outdrive connects between the upper housing and lower housing.  The reason it didn't do it at lower speeds was becasue the entire outddrive was in the waterand instead of air it was sucking in water.  When the boat planed only the lower housing was in the water and caused the overheating becasue the connection between the upper and lower housing was out of the water and sucking air instead of water.   I hope this helps as it drove me crazy for a while.