VP 5.0 GIPEFS running cold

[4Winns24]

Hello Everyone,

My engine is running at about 100 degrees. My temp gauge is always cold and my IR gun shows 100 or less across the engine. It is an injector engine and someone experienced told me it has to run at 160 or my injectors won’t work properly. Is the problem with my thermostat and does it need to be changed?

 

[alldodge]

Is the problem with my thermostat and does it need to be changed?

That would be were I would look first. It may be stuck open

Could remove and place in water on the stove. As water heats up watch for when it opens

 

[Lou C]

Common problem, all it takes is a flake of rust or grain of sand and the stat won't close all the way. I have a supply of spare stats, gaskets and the rubber ring that holds the stat in the housing. When you remove the housing and turn it over you will see the ring (probably covered in rust) that fits into a groove in the housing this is what hold the stat in. You will have to dig it out with a very thin screwdriver or a pick. If your housing is all rusted up, with the water passages getting necked down, you can dig out the rust and re-use but if there is a ton of flaking rust I'd replace it. What I've found is that you will notice flaking rust in the bottom of the intake manifold right under the stat, this is what likely causes this chronic problem. One more reason why raw water cooling is a lousy idea and all cast iron inboards should have at least a half closed system, so they can operate like GM intended them to.

 

[4Winns24]

Just out of curiosity, what kind of damage does running cold at about 100 degrees cause to salt water engine?

 

[BRICH1260]

I had a similar problem in a 5.0 gxi that I had in my last boat. I found that the thermostat bypass lines inside the thermostat housing were clogged up. I took the housing off and with a piece of wire cleaned out the passages. It resolved the problem.

 

[alldodge]

Just out of curiosity, what kind of damage does running cold at about 100 degrees cause to salt water engine?

Its just going to run a bit richer, which may require plug cleaning/replacement. Could coat the sensors which would cause them to not read correctly.

 

[Scott Danforth]

Just out of curiosity, what kind of damage does running cold at about 100 degrees cause to salt water engine?

it will run richer like AD stated, however running below 140 also significantly increases wear on the motor

change the thermostat, fix the issue, and go boating.

 

[4Winns24]

Thank you everyone for your very helpful input.

Is there any truth to what some people say that at 160 degrees salt deposits will damage the engine and that it is best to keep the engine at around 140 in salt water?

 

[alldodge]

Lower temps are better for salt water, how much difference between 140 and 160 is there but not a great deal. The 140 is better, but your motor is set up for 160 so far as the tune.

 

[Lou C]

I took apart my OMC 4.3 to do a top end overhaul about 3 years ago that at that time was used in salt water at least 15 years with the 160 stat and did not find any evidence of salt deposits. This is Long Island NY salt water. Maybe in Fla & the Gulf Coast this could happen but I saw no evidence of this....

 

[bruceb58]

Also, if running cold for a long period of time causes the engine not to be able to get rid of condensation in the oil. On my outboard, I found about a half a cup of water in my crankcase. When I checked for error codes on my engine, I found an under temp warning. That pointed me to the themostat that was stuck open.

 

[Lou C]

Agreed on both points, running too cold increases wear due to excessively rich fuel mix contaminating motor oil and also condensed moisture does not get burned off. In fact some outboards have a problem with 'making oil' which is actually fuel dilution of the oil and one of the specs for Marine motor oil is that it has to lubricate with a certain level of fuel dilution. I've found that in salt water I can go as much as 2 seasons on a thermostat, but never longer than that, then you get the cold running blues where it will get up to approx. 120* until you run it on plane when it will hit 160 but if there is still debris in the stat it will still run cold at idle. I found a way of jarring loose rust or sand in the stat, run the engine up on plane, so you know the stat is all the way open...then before it cools off tap on top of the stat housing gently (works fine on OMC/Volvo cast iron housings) with a small hammer and those vibrations can loosen and dislodge a flake of rust or bit of sand. I would NOT do this on an alu alloy housing on an OB though.
If that doesn't do it then you have to pull it out. I keep a spare stat housing with the stat already installed and a plug for the raw water intake hose on the boat just for this reason. I have changed them on the mooring a few times....

 

[Scott Danforth]

Thank you everyone for your very helpful input.

Is there any truth to what some people say that at 160 degrees salt deposits will damage the engine and that it is best to keep the engine at around 140 in salt water?

as the water temp crests 145-150, certain salts in sea water become insoluble and drop out as crystals, increasing wear due to abrasion. for these reasons, its best to keep salt water motors as cool as possible. However not too cool. the compromise temp is 140

the first salt to drop out is Calcium Carbonate, followed by Gypsum, then Sodium Chloride. all found in seawater.

it has to do to solubility curves, temperature, etc.

 

[Lou C]

I looked for a while but could never find a 140 stat for the OMC/Volvo housing. I know Mercruiser did spec that on their older engines though.

However, while I did not SEE evidence of crystals, perhaps what you are referring to here is what the machinist said about my old heads, the cooling passages were getting eroded, so the heads if re-done might not seal properly. I think it maybe that the cyl heads suffer more than the block in salt water...

 

[4Winns24]

So I finally found the time to change the thermostat. I ran the boat for over 30 minutes but I still couldn’t get the temperature to go above 150. It played between 140 and 150. Interestingly, when I plained, it was closer to 140. But overall it stayed around 145ish, which is still alot higher than 80 degrees she used to run at. Is that a pass in your opinion?

 

[4Winns24]

Here is a picture:

 

[alldodge]

I would say your good, go have some fun

 

[4Winns24]

I would say your good, go have some fun

Thanks

 

[Lou C]

agreed that looks fine!

 

[4Winns24]

Thank you for all your help. Another question: I noticed that my spark plugs were carbed up couple of months ago when I changed my exhaust system. Now I know it was because engine was running rich, and also the boat had been sitting for a very long time.

Do I need to clean the spark plugs up or change them? Or with the engine running at right temperature, they will clean up gradually on their own?