4.3GL still overheating after multiple cooling system part replacements

[birdpiper]

Volvo Penta 4.3GL PWTR, 1999, 190 HP

Looking for any advice on what to try next. We replaced multiple components of the cooling system recently, but the engine is still overheating slightly. Don?t have a digital thermostat, but if the temperature gauge on the dash is broken into 1/8?s and normal temp is in the middle at 4/8, it is currently reading at 5/8.

- Both sets of manifolds and risers are fairly new, replaced within last two seasons
- Replaced the impeller
- Replaced the thermostat
- Replaced the re-circulator pump
- Removed all hoses on engine and checked for obstructions
- Removed and cleaned the thermostat housing (it was corroded, but it didn?t look like anything was restricting flow)
- Flushed the manifolds by removing their drain plugs and running water through their hoses from the thermostat housing.
- Replaced the raw water pump (this was obviously leaking)

The raw water pump was the most recent replacement. After replacing that it ran for about 5 hours with no issues. The overheating came back a few days ago. When I investigated, the port side manifold felt hotter than the starboard side.

I?ve looked through the VP overheating diagnostic manual, but setting up clear hoses with gauges is probably a little above my skill level.
We are probably going to haul it back to the mechanic soon, but wanted to see if there are any other quick checks to perform first. The mechanic usually takes a month+ this time of year (July).

 

[alldodge]

Your gauge might be bad. Get a IR temp gun and measure the temp at the thermostat housing

 

[birdpiper]

Thanks for the feedback. I plan to pickup an IR temp gun on Amazon in the next few days. The temp gauge may be bad, but I imagine that is low probability.

 

[alldodge]

Thanks for the feedback. I plan to pickup an IR temp gun on Amazon in the next few days. The temp gauge may be bad, but I imagine that is low probability.

Is it to hot to touch?

 

[birdpiper]

Very warm, but not hot. I could hold my hand on either manifold, the thermostat housing was a little bit warmer, but not too hot to touch.

 

[Lou C]

You need to get an IR temp gun and take readings, if you read the intake manifold right below the thermo housing, it should read a bit lower than the dash gauge, mine usually reads 150-155 right in that spot. Manifolds, at idle no load they should be about 100*F (warm not hot) and after coming off plane, they may get as hot as 135-140, but they should cool back down pretty fast. 140 may be too warm to keep your hand on it.
​Does it overheat at idle, or only after running on plane?
​if at idle, then your raw water flow may be low, this can be checked with the boat in the water. If low, make sure there are no air leaks in the impeller housing.
​If on plane, then the clear hose test is the best way to tell if air is getting sucked in and aerating the cooling water flow. It is not hard to do, I did it on my OMC Cobra a few years back. You need a partner to watch the hoses while you drive.
​There is also a plastic fitting in the transom mount, that can crack due to age or freeze damage, and this can allow air in.

​these open systems depend on a high volume of cool water in, and out. Anything that interrupts this flow will cause elevated temps.
​Normal temps on these should be 160-175, not over 180. Make sure the thermostat is not sticking and opens all the way, and that the passages feeding the manifolds are open.

 

[RCSConstruction]

One will always run hotter than the other. (riser)
Maybe the new T-stat is opening up at a little higher temp than old one?
Is it a saltwater boat? Try a salt-away flush?