Mercruiser 888 missing thermostat, running hot

[twentybelow]

I have a mercruiser 888 motor that runs around 220 degrees.

I bought the boat a short time ago after a test drive where i could of sworn i saw the temperature gauge hit 200 and then go back down again to around 160. Hence, i assumed "oh good, there goes the thermostat, working fine". Later on during the test drive the motor lost a freeze plug and burnt the left exhaust boot before the motor was shut off. I bought the thing, pulled the engine, replaced freeze plug, cleaned up oil pan, put engine back in boat, replaced coil, and started it up. I have outdrive pulled and a hose routed straight to the inlet hose to water pump. I ran motor long enough for temp gauge to hit 220 and sit there for a minute.

This is way too hot, i have manual, it says something about thermostat opening at 160.

I Pulled thermostat housing off.........no thermostat.....

now....i am thinking engine should run cool instead of hot with no thermostat.

Is this just a preview of cooling issues i have yet to discover? I will order thermostat but need some free advice.

 

[twentybelow]

Re: Mercruiser 888 missing thermostat, running hot

reposting

 

[jtybt]

Re: Mercruiser 888 missing thermostat, running hot

Probably!

 

[twentybelow]

Re: Mercruiser 888 missing thermostat, running hot

Probably!

i appreciate all your help. I have a tuna boat to china you might want to check out.

 

[bruceb58]

Re: Mercruiser 888 missing thermostat, running hot

Your manifolds are possibly plugged up. Take off the elbows and look inside to see if there is blockage. Has this boat been run in salt water?

 

[JustJason]

Re: Mercruiser 888 missing thermostat, running hot

eagh.... you can start with the manifolds... or you can start with the water pump... Either way you need to go through your entire cooling system. If you burnt a rubber BruceB may be on the right track in checking the risers. But ya have to check everything.

 

[bruceb58]

Re: Mercruiser 888 missing thermostat, running hot

I reread the first post and you say you put the hose into the inlet of the engine water pump? That's not a good way to test things.

I agree with jason, You need to look at the water pump impeller in the drive. When you made the first statement, I though you had pulled the drive and had the hose going into the water inlet into the boat.

 

[twentybelow]

Re: Mercruiser 888 missing thermostat, running hot

I reread the first post and you say you put the hose into the inlet of the engine water pump? That's not a good way to test things.

I agree with jason, You need to look at the water pump impeller in the drive. When you made the first statement, I though you had pulled the drive and had the hose going into the water inlet into the boat.

The drive is pulled and laying on the bench and i pulled off the main water hose going to the transom and hooked up water hose. The motor has been in and out a few times so far and i don't want to start messing with the drive until i am sure the motor won't have to be lifted out again for something.

This is how i have tested the motor from the beginning. I turn the water hose on and then start motor. As soon as I turn on water it starts coming out the exhaust area on outside of boat.

I will go through and PM the impeller when it comes time to cross that bridge. Right now i need to get the engine temp down or start pricing a new block. I will do as advised and start going through the manifolds and check out the main water pump...maybe just replace pump for good measure, there is one on ebay for 125 bucks.

 

[twentybelow]

Re: Mercruiser 888 missing thermostat, running hot

Your manifolds are possibly plugged up. Take off the elbows and look inside to see if there is blockage. Has this boat been run in salt water?

Don't know if it has been in salt water but the water jacket (from what i have seen in the thermostat housing) is pretty rusty looking, little pieces of rust inside floating around. I looked up through bottom of motor when i had the pan off and the cylinder walls seem in excellent shape and i see it being a strong runner if i can get the temp down. I will order some gaskets and start going through the manifolds.

 

[Apollo75]

Re: Mercruiser 888 missing thermostat, running hot

There is not much to the cooling system --- However, I think the whole impeller is weak at low rpm's like trolling --- I run warmer at low rpms. Cools down nice running at cruse 3000-3400 rpm's.

1975 Apollo 302/888 -- still runs nice


Good Luck

OFM