Starboard engine temperature low

[Split Decision]

I have a 2001 328 Vista with the twin 5.7 litre GSI Volvo Penta sterndrives.

After starting both engines from cold, both engine temperature gauges will slowly raise in temperature until about 160 - 170 degrees where at idle they stay there. However as soon as I get up on plane the starboard engine drops back to about 140 degrees and pretty much stays there until I come back off plane where the starboard engine will to go to about 160 - 170 degrees and hold there while at idle. Get back up on plane and again the starboard engine drops to 140 degrees. The port engine pretty holds 160 - 170 degrees at idle or on plane.

I thought thermostat and had the marina change the starboard one. After change the same condition exists. I asked marina to confirm they did change starboard and not the port.

Any thoughts, if they did change the starboard thermostat and my starboard engine continues to drop in temp when on plane?

 

[Gregory S]

What temp are the thermostats and are they both the same? Do you have raw water cooling or closed (fresh water) cooling?

 

[Sandy]

Suggest checking temps at the thermostat housing with an IR temp gun and testing the t-stat in a pan of heating water with a candy thermometer as reality checks. The new t-stat could be sticking even if they did put in a 160 and not a 140 by mistake.

As Gregory asks above, are these engines RWC or FWC?

 

[Split Decision]

Engines are raw water cooled. We boat in the fresh water great lakes.

You guys know better than I, but could the way my starboard engine goes from a 160 - 170 degree temperature at idle to 140 degree on plane be anything but a thermostat issue?

I do have a IR gun, so I could take those temperature readings this weekend.

I guess I shouldn't assume the marina put the same thermostat in each engine, so I guess there is a possibility the starboard is a 140 degree instead of a 160 like the port side.

 

[Michael Clemensen]

This cold running happens a few times to my 1996 VP 5.8FSi each spring. Raw water cooled, Cold lake water temperature, 160 degree thermostat, scale from sitting dry all winter flakes off and gets stuck under the thermostats top hat as it gets a chill from the raw water. It’s happens less frequently if the thermostat has a small “V” cut out on the perimeter of the top hat. I pull the thermostat housing and push up on the bottom of the thermostat, the scale flows out, button it up and its fine again. High RPM operation with the additional water flow will cause the scale to flake off. After the lake warms up and the power plant has a few hours run time the problem doesn’t reappear until next spring. Again this power plant is on its 19th season.

 

[jtybt15]

Wellll, the function of the thermostat is to regulate the water temps. It's either the thermostat or a sticking ball in the thermostat housing. The balls regulate flow direction to by-pass engine.

I've seen some funny things like one engines cooling system plumbed different from the other.

Oops! You have VP. No BALLS[:I]

 

[Split Decision]

Just to follow up on this thread....

I did use my IR gun and shot the top of the thermostat housings of both port and starboard engines while at idle after engines warmed up and again up on plane with engines spinning about 3400RPM. The IR gun confirmed the starboard engine was indeed running about 30 degrees colder on plane as compared to the port engine and both engines ran very close to the same temperature while at idle.

I conveyed this information to the marina and they confirmed that yes they did put the correct 160 degree in the starboard engine, they had put a thermostat kit in the starboard engine and had removed the thermostat housing to clean and reinstall.

They agreed they would take another look since my IR gun readings confirmed the work they did did not resolve my initial work order.

When I returned to the boat after their 2nd look, I noticed I had a different thermostat housing now on my starboard engine. Starboard one was now black in color where it had been grey before. Took the boat out for a ride and sure enough the starboard engine now on plane reads about 170 degrees and matches with the port engine temperature.

So now I have two invoices, the first was for installing new thermostat kit and removing cleaning existing thermostat housing) and the second for 2 hours labour to change out thermostat housings and the cost of a refurbished thermostat housing.

 

[LouC]

On those thermostat housings, there is a bypass port, and when it get clogged, because of the way that water flows through the housing it can force the stat open at speed, causing the problem you saw. The cold running could be that, or flakes of rust keeping it from closing. I have also had this problem on and off and its common with raw water cooled engines. BTW, my OMC uses the same thermo housing as the Volvos (Volvo copied the OMC design) and the most accurate reading is taken from the intake manifold right below the thermo housing. This usually gives you a reading about 10* lower than the dash gauge. So if you have 150* at the manifold you will have 160* on the gauge.
If the stats don't close because of rust, what I have tried, and it works, is this:
Get the boat up on plane, so the temp reads at least 160, slow down to idle and get a small hammer and tap on the top and sides of the thermo housing. This can dislodge the rust particle and allow it to close restoring normal temp readings.