2002 Volvo 5.0 GXI Low Operating Temperature

[csukraw]

Replaced the thermostat with an OEM 3856961 end of last season because I was having overheating issues, fixed the issue (old one had gravel and sand in it and was sticking partially shut). Now this season on our first trip out to Havasu last week (water temp was 80 degrees), it seems my engine is running too cool. Manual says normal operating temp is 155-175. I don’t check the gauge religiously when running but I’m pretty sure it usually hovered around 155-160 or so. Last week, after pulling the tube for an hour doing around 25mph off and on I noticed it was barely above 120. Then later after running high speed for a good 15-20 minutes it barely got to 145-150. Is it possible my new thermostat is not working properly and sticking open? Or maybe my gauge is off?

 

[alldodge]

Thermostat is stuck open, or was removed and not replaced, or somehow was not installed correctly and some how is allowing water to by pass it. Either way need to get back into the thermostat

 

[Donald0039]

There are thermostats for raw water cooling and closed cooling. You need the right one for your type of cooling.

Take the thermostat out and tie two feet of string to it. Heat up a pan of water with thermostat suspended in middle of the water. Use a thermometer to see when it opens. You don't want the thermostat picking up heat from the pan (metal to metal transfer). Thus tie string to it and suspend in the water.

 

[csukraw]

I'll have to do some troubleshooting. I won't be able to remove and check the thermostat / gauge till after my next trip. Is there any risk of damage with it potentially cooling off the engine too much for one trip?

 

[alldodge]

I'll have to do some troubleshooting. I won't be able to remove and check the thermostat / gauge till after my next trip. Is there any risk of damage with it potentially cooling off the engine too much for one trip?

No so long as your not boating in salt water. Even in salt it would take time to build up to be an issue. Your just going to burn more gas

 

[ESGWheel]

The sand and gravel may have done some harm to the Raw Water Pump (RWP) as well. While expect the opposite effect with a RWP not pumping as expected (ie overheating), when you get back into the t-stat recommend you also pull the cover off the RWP and inspect the impeller and casing to see if all that grit had a negative impact on it.

Also recommend not waiting to inspect the t-stat before getting a new one along with the needed gaskets / O-ring. And test the new one as Don suggests once in hand, to know it’s good. Then, when doing your investigation, you know you have a good unit to replace the other and you can, at your leisure, figure out about the other. That way you can get into the job and complete it as one event. Heck, get another RWP impeller as well just in case that inspection shows wear. And if not you have one for the next season.

 

[csukraw]

Yeah replaced the thermostat and impeller end of last season so I'm good there. Old impeller looked fine but replaced anyways.

 

[BRICH1260]

Check the bypass passages inside the thermostat housing for blockage. They are hard to see unless you remove the housing and look way up inside.

 

[Lou C]

The other thing that's a common problem, is a grain of sand or rust flake caught in the 'stat, it keeps it from closing, it will never warm up till you run it on plane for a while. Sometimes that clears it out. I've also had luck with running it up on plane, bring it back to idle, and then tap on the stat housing with a small hammer to dislodge the particle. Don't laugh it has worked for me at least 2x.

 

[Scott06]

I'll have to do some troubleshooting. I won't be able to remove and check the thermostat / gauge till after my next trip. Is there any risk of damage with it potentially cooling off the engine too much for one trip?

Would also test the thermostat housing with an IR gun to see if gauge is off.

If you take the thermostat out you can test it in a pot of water use a meat thermometer to see what temp it starts opening at