Perplexing engine temp issue. 5.0 GL-B

[Misterbulbous]

Looking for some thoughts on two issues I’m having with my 5.0 carbureted GL-B.

1. Temperature sender in thermostat housing is alarming out before and after changing the thermostat and impeller. This is second summer with problem. Temperature at dash panel shows no signs of overtemp (slowly rises and stabilizes at 170). I don’t assume it’s the sender because I think it’s truly running hot. The cooling water is definitely reaching the thermostat and risers, but the intake manifold, thermostat housing and “large” hose exiting housing is very hot.

This is brings up 2nd problem - which seems to be vaporlock from the hot conditions.

My question...assuming raw water pump is good, thermostat is good, sender is good, is there another reason the temp would be high?

Generally speaking, the engine is in excellent condition. Always winterized, never stored outside, well maintained. But...the issue above has sustained for two seasons now.

Thoughts?

 

[Scott Danforth]

.assuming raw water pump is good,

Thoughts?

dont assume....change it and back-flush the system.

high temp is the sign of low water flow

if you have an AQ series of drives, look at the raw water inlet casting, they rot off the boat in both fresh water and salt water. early SX drives had the same crappy material on the inlet fitting. wasnt until later that they changed to plastic...which just breaks off after a few years.

 

[Misterbulbous]

^ I appreciate the response. The hose from the water pump to the manifold feels cool when running, the two hoses from the manifold to the risers also feel cool, which leads me to believe the pump is doing it’s job. (Obviously I don’t know if flow is good, yet). Basically I don’t understand why the engine temp sensor shows 170°, but the sender at the thermostat housing is reading high temp and that area seems overly hot. When I disconnect, the alarm stops...and actually not sure where the dash gauge is receiving it’s info from because it doesn’t react to thermostat sender disconnect.

Fought this issue all all last year, changed impeller and thermostat and boated for two days this year without alarm, but now the alarm has returned.

I agree to backflush, but also wondering if there is another Issue causing the alarm.

 

[Scott Danforth]

you have a lack of flow issue.
your running warm
find the lack of flow (either a blockage, or your also sucking air from the inlet fitting/casting)

 

[jimmbo]

There are two temp sensors. One is for the alarm, the other is for the gauge. 170 is too hot. What is the opening temp of the new thermostat?

 

[Misterbulbous]

There are two temp sensors. One is for the alarm, the other is for the gauge. 170 is too hot. What is the opening temp of the new thermostat?

Thanks for the reply. The thermostat is the correct part from the VP online store (I don't recall the opening temp). Plan of attack for now is to check for anything blocking water flow and/or drawing in air.

 

[Misterbulbous]

think i may have found the problem, but looking for other confirmation before I tear into it further. I removed the impeller and housing (without rotating it) and the orientation of the fins is crossed. I would think these would self-align during rotation, but maybe not? Obviously I will re-orient.

 

[4now04]

Since you have it apart, I would recommend replacing the impeller if possible and available. Normlly the impeller would correct itself. Since it didn't you might want to start over with a new one.

 

[Misterbulbous]

Since you have it apart, I would recommend replacing the impeller if possible and available. Normlly the impeller would correct itself. Since it didn't you might want to start over with a new one.

Yeah. Unfortunately, I just rotated the impeller a few degrees by hand and all the vanes popped into the correct orientation. So, I'm still not convinced that I didn't cause this condition when I removed it. Of course, it may be different when connected to the water pump spline. I have noticed that the inlet and outlet plastic tubes attached to the housing spin a little (and i don't think they are supposed to), so it could be sucking air a little bit (?)...

 

[Misterbulbous]

Welp, for those following my drama here. I may have found my issue. Removed the thermostat and ran a few hot water trials and it opens up around 175 degrees. I believe my boat "prefers" a 160 thermostat. In shopping around (amazon, west marine, VP store, etc) i noticed that the same volvo penta part number can yield a few different results for the correct replacement. I ordered a 160 degree thermostat and I'm hoping that stops the alarm coming from the thermostat housing.