383 stroker half closed cooling running hot

[cruiser262]

Hi Everyone.

I am running into this problem.Brand new mercruiser 383 stroker freshwatercooling with 160F thermostat.The dealer in Us where i bought it from(Michigan Motorz) installed half fresh watercooling systemand replaced the dryjoint exhaust manifold and risers with the wet joint one because he said that freshwatercooling he installed was not compatible with the dry joint exhaust system.Now the issue
when i go idle temperature stays steady at 158F.If i increase to 3000 rpm goes to 176F if i increase to 3200 goes to 185 if i try pushing to 3400rpm it stays for a bit then it reaches almost 194 then the engine guardian sounds and disconnets the throttle...as soon as i go at 3000 or less temp immediately drops to 176 or below if i go idle.Outside temp here is 104F right now so sea water temp is warm as well.Should i install a 140F thermostat since it opens earlier and keeps the engine colder?I am going to check impeller and risers as well but the engine is brand new i suspect more a thermostat issue.Is there any difference in water passage size between dry joint and wet joint exhaust elbows and manifolds?

 

[Scott Danforth]

check for obstructions in the cooling system from the drive pickup to the raw water pump. then from the raw water pump thru the heat exchanger to the manifolds. somewhere you are loosing flow

is this an aftermarket half system, or the mercruiser 6-pass factory heat exchanger? have you pulled the end caps to look to see if you have debris in the HX tubes?

edit - how warm is your sea water? they system was designed for 95 degree water max if it is the factory system

 

[Walt T]

Impeller. Maybe replace the housing too

 

[cruiser262]

Hi Scott and Walt
Cooling system is System is San Juan. yesterday i bought a 140F thermostat since this closed cooling system shows having the 160F one.
today the water temperature went from from 92 to 94.3 and it is going to be like that for other 2 weeks since outside temp is 104

 

[cruiser262]

Gentlemen one more thing

is it possible to change the thermostat in the San Juan cooling system?I bought a 140F as i said before but since now the thermostat is in the heat exchanger and no longer where it used to be...

 

[Scott Danforth]

I would call San Juan.

 

[HT32BSX115]

Hi Everyone.

I am running into this problem.Brand new mercruiser 383 stroker freshwatercooling with 160F thermostat.The dealer in Us where i bought it from(Michigan Motorz) installed half fresh watercooling systemand replaced the dryjoint exhaust manifold and risers with the wet joint one because he said that freshwatercooling he installed was not compatible with the dry joint exhaust system.Now the issue
when i go idle temperature stays steady at 158F.If i increase to 3000 rpm goes to 176F if i increase to 3200 goes to 185 if i try pushing to 3400rpm it stays for a bit then it reaches almost 194 then the engine guardian sounds and disconnets the throttle...as soon as i go at 3000 or less temp immediately drops to 176 or below if i go idle.Outside temp here is 104F right now so sea water temp is warm as well.Should i install a 140F thermostat since it opens earlier and keeps the engine colder?I am going to check impeller and risers as well but the engine is brand new i suspect more a thermostat issue.Is there any difference in water passage size between dry joint and wet joint exhaust elbows and manifolds?

Howdy,

The ability of that heat exchanger to remove heat from the coolant is dependent on a couple of things, It must be "big" enough and the raw water flow must be adequate.

If this is a half system, it doesn't matter if you have dryjoint or not. You're NOT cooling the manifolds with coolant, you're cooling them with Raw-water.....

If it's a FULL system (I. E. You're cooling the block AND manifolds) and you're using a heat exchanger only big enough for a half-system, it may over heat at higher power (WOT) settings in warm water. (The risers are ALWAYS cooled with raw water in either system)

Changing your T-stat won't make any difference. A 160 is the right one. If the temp makes it up to 170-175, that's pretty much normal. (I see 180 once in a while with my 454 (Full closed cooled) running at WOT.

If it's exceeding about 180 or so, your raw water pump might not have enough output. (Is this an Alpha or a Bravo?)

There have been *some* issues in the past using Alpha raw water pumps supplying closed systems.....possibly because of inadequate flow of raw water through the heat exchanger.

You should ensure that you have enough raw water flow and you have the plumbing hooked up right.

I have run my 454/Bravo at WOT in 85 degree water and not had the coolant temp go above 180. (mine is a San Juan [full] System I installed in 2006)


Regards,


Rick

 

[Scott Danforth]

I agree. the alpha pump can only supply 19 psi at about 19 gpm if you add much restriction to the raw water flow, it starts dropping off. This is the minimum for a half system.

You are also in an area of high water temps. traditionally most of the heat exchangers are sized for 95 degree raw water and 165 degree glycol. Since you stated your water temp is in this range, you are at the limit.

as far as heat rejection goes, approximately 1/3 of the fuel's BTU's go out the tail pipe, about 1/3 goes into the cooling system and about 1/3 out the crank shaft. So a full system needs to transfer double the BTU's of a half system

Depending on the build of the 383, you may be into heat exchangers sized for big blocks (5" diameter vs the 4")

regarding dry joint vs wet joint. As Rick mentioned, this doesnt matter as you are cooling the exhaust with the HX outlet on a half system.

 

[cruiser262]

Many thanks for your suggestions Gents.
Regarding the drive...I have a volvo penta dps-m duoprop 1.95 drive adapted to the mercruiser 383 stroker (I changed the flywheel housing and coupler of my previous hydrolocked vp 7.4 gi engine)Is a huge drive and I think that water intake from the drive is big enough.regarding my closed cooling system capacity michigan motorz mechanic suggested me to installl a 140F thermostat and drill 2 holes on it or purging the air that might have been still in the system causing the temperature to increase. This option sounds strange to me because I cruised already 4 hrs when I took the boat fm the shipyard to my marina plus 3 hrs already done when I first seatrialed the boat by the shipyard marina after the new engine was installed.Is it possible that there is still some air in it?Anyway I am going to vhange thermostat and let you know meanwhile each suggedtion will be appreciated
many thanks Gents

 

[Scott Danforth]

The Volvo/ITT jabsco pump will have plenty of flow. How is the water intake housing on the drive? It is a weak point in the Volvo suction side plumbing

 

[cruiser262]

I will check and let you know Scott...the boat just came out from the workshop after antifouling and new engine installation...the drive water intake should be clear...hopefully

 

[Scott Danforth]

If you boat in salt water the casting corrodes quickly. I epoxy coated my last one to see if I can get more than 3 years out if it.

 

[Bondo]

If you boat in salt water the casting corrodes quickly. I epoxy coated my last one to see if I can get more than 3 years out if it.

Ayuh,..... Couldn't ya go to a sea-****,..??

 

[bruceb58]

Add a clear hose in the raw water suction path temporarily to make sure you are not sucking air.

 

[cruiser262]

Scott i looked at the sea water intakes on the drive...they looked clear.I opened the thermostat housing 2 days ago...there was a 140 F installed with two hoses drilled on it.I removed it and run without it...same result ,above 3200 rpm temperature slowly increased till the engine guardian steped in and disconnected the throttle.I called the dealer and asked for clarification...he said that they started drilling holes on thermostats by defaul since few months ....hmmm it doesn't really sound true to me!Then he told me to bleed the air off the cooling system properly because most of the times the problem is that one.Then he mentioned that since i m operating in warm waters(94F) and my engine is a 383 stroker MPI freshwatercooled the coolant temperature will struggle to go down till the seawater going into the heat exchanger will be that warm....

 

[dypcdiver]

I think he sold you too small a heat exchanger, or the flow through it is restricted somewhere.