Engine Temperature Spikes

[Jilly - 5]

Have a 302 Ford FWC in my 21' Nova, with thru hull raw water pick-up (I/O pick-up is capped off in bilge). Have 160 thermostat. Whether idling or underway, the temp will spike from 160 to 200, then come back down to 160 (steam out exhaust prop hub). May do this 5 or 6 times underway, then temp settles in at about 180 on the long haul.<br /><br />Is this a bad thermostat, or do I have manifold/riser problems? M/Rs were new in 1999.

 

[tommays]

Re: Engine Temperature Spikes

jilly<br /><br />a bad connection can make the guage jump around you need to be sure it really getting hot 200 is very hot if its correct<br /><br />try the simple thing first change the stat and check the condition of the raw water pump<br /><br />1999 to 2005 if the boat is in saltwater can be a long time for manifolds/risers <br /><br />how and were is the boat used and is the FWC a hafe or full system<br /><br />tommays

 

[Boatist]

Re: Engine Temperature Spikes

A bad connection is not going to make steam out of the outdrive. I would start with the simple and most likely thing the thermostat. <br /><br />Make sure the thermostat air bleed hole is not plugged up. I some times drill them a little bigger. Make sure it is installed the right direction, spring and plunger side toward the block. Put in a new thermostat they are cheap. Before you install it put both in a pan of water on the stove and watch when and how they open. Don't tell the wife your useing her cooking thermometer. I got two of my own now so do not need to use HER'S. I seen a lot of thermostat get stuck where it did not want to open or close and instead of opeaning normaly nice a slow and even it would stick then almost pop open. I also see debree in the thermostat cause it to stick open.<br /><br />Only other thing I can think of is to make sure block is filling with water. I do not think it will be a manifold as they are usually ok at idle but engine get hot at High speed when they first start to go. Of course it can be your water your raw water pickup. If block is not filling with water then nothing to heat the thermostat.<br /><br />Please come back and report on the fix.