Volvo Penta 5.7L Cooling problem

[HawaiianHooker]

Last year I replaced my motor with a re-manufactured short block from Jasper but since then I've had a strange cooling problem.

When the motor first starts up and warms, it will keep getting hotter and hotter until I put it in neutral and rev the motor, then it will start cooling back down to normal. It's as if the thermostat is sticking but I'm on my 3rd one now and the problem persists. What's even stranger is that it does this much more noticeably when It's out of the water using the rabbit ears as opposed to being in the water. This is raw water cooled, has a new sea water pump as well as the circulation pump (known as water pump for automotive) which was a GM part though, not Volvo.

Any ideas what could be causing this? Could I have got a bum motor from Jasper that has an old thermostat stuck in the block?

 

[alldodge]

Does it worst on muffs then in the water but still does it, sounds like the impeller and pump housing, or your sucking air.

 

[Scott Danforth]

volvo penta drives have issues with the water inlet casting or fitting. if it is the AQ series drive, it is the water inlet casting. if it is the SX series, the water inlet threaded hose bib connection fails. in either case, pull the drive and check. there first

and you cant get a thermostat stuck in the block..... that is physically impossible for the thermostat to make it from the intake thru the water port thru the head to the block unless you use dynamite