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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11079
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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318 Chrysler Marine engine, raw water cooled. Replaced thermostat

Customer Question

318 Chrysler Marine engine, raw water cooled. Replaced thermostat & sensor on leeward engine as it is running very cold. The temp gauge was tested and works fine. The manifold is cold. Engine continued to run cold with new thermostat.
Replaced with housing & thermostat from starboard 318 Chrysler engine as it was running per specs. No change, the leeward engine continues to run cold.
Installed the new thermostat on the starboard engine and it gets to operating temp. just fine.
So the thermostat and sensor is to the problem.
What could it be?
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello my name is ***** ***** am I speaking with? When did this problem start, when did it last heat up?
Expert:  Jason replied 2 years ago.
Can you take a few pictures of the front of the engine so I can see how all of the plumbing is laid out, the more pictures the better.
Customer: replied 2 years ago.
It has been this way since we put her in the water. The Starboard engine operates per spec, the leeward engine will not heat up. It was working fine last season. The plumbing has not been changed. Harry
Customer: replied 2 years ago.
Could it be the water pump?
Expert:  Jason replied 2 years ago.
No it's not the water pump. For it not to heat up water has to be circulating and leaking past the thermostat somehow. Whether it is incorrect plumbing, a crack or rot hole someplace. It hast to be leaking past the thermostat. Does that make sense?
Customer: replied 2 years ago.
We replaced the thermostat and housing with a new thermostat. That did not fix it. We then took the starboard thermostat and housing, which works fine, and put it on the leeward engine and it will still not heat up.The thermostats are not the problem.With the thermostat housing removed from the starboard engine we could see the water level staying even with the engine block. The water level on the leeward engine (the problem engine) does not stay even with the engine block. The water drains into the block. Could that be sign of something?
Customer: replied 2 years ago.
There is no water leaking out of the engine or any fittings or hoses. The engine compartment is dry as a bone.
Expert:  Jason replied 2 years ago.
Thats why I was hoping to see a picture of everything. Water is leaking past the thermostat some how. If the plumbing is correct then the block is cracked someplace. But does that make sense that water is leaking past the thermostat?
Customer: replied 2 years ago.
Okay - I will take some photos. Give me a few minutes.
Expert:  Jason replied 2 years ago.
Okay. The more pictures you can take the better. Try and show all of the hoses and plumbing so I can see everything
Expert:  Jason replied 2 years ago.
Can you take few more that are more of a birds eye view showing the entire front of the engine, and entire top of it. I want to be able to see everything all at once.
Customer: replied 2 years ago.
Expert:  Jason replied 2 years ago.
Nothing came through. Did you upload the new pictures?
Customer: replied 2 years ago.
Expert:  Jason replied 2 years ago.
Those are better thanks. Have you ever seen this engine heat up properly since you have owned it?
Customer: replied 2 years ago.
yes, for the last 6 years.
Expert:  Jason replied 2 years ago.
So it's safe to say you haven't touched any of the plumbing/hoses, correct?
Customer: replied 2 years ago.
correct the hoses/plumbing has not been changed and are identical to its twin starboard motor.
Expert:  Jason replied 2 years ago.
Is there any way you can take another picture so I can see how the thermostat fits in the housing?
Customer: replied 2 years ago.
Not now, my technician swapped the thermostat housing on both engines and used up all the extra seals.He put the leeward engine thermo and housing, which was new, and put them on the starboard engine and the engine heats up properly and records 158 degrees on the gauge.He took the starboard engine thermo and housing, which was working just fine on the starboard engine and put that on the leeward engine to see if that would work (it did not.)I have no extra housing seals and will have to order more before we try and remove the housings again.
Expert:  Jason replied 2 years ago.
I'm out of ideas. I will opt out.
Expert:  Tan replied 2 years ago.
Hello. My name is***** you verified with a IR temp gun the engine is actually running cool? Have you inspected the intake manifold where the thermostat sits? Is the intake rotted out where the t-stat sits?
Customer: replied 2 years ago.
My technician did not use a IR temp gun. The leeward engine manifold is outright cold compared to the starboard engine manifold.
My technician is due back here next week and we will check to se if the intake on the leeward engine is rotted out.
Expert:  Tan replied 2 years ago.
The only thing that controls temp on your engine is the t-stat. You have eliminated the t-stat housing and the t-stat leaving the intake where the t-stat sits. If water can get around the t-stat it will run to cool. Now we need to verify that the engine is running cooler than 150*F. Is it possible the other engine is running hotter than 150*F. Post back with findings and questions.
Customer: replied 2 years ago.
With the thermostat housing removed from the starboard and leeward intake manifolds we could see the water level staying even with the top of the intake manifold on the starboard engine. The water level on the leeward engine (the problem engine) does not stay even with the intake manifold. The water drains out of it through a corroded hole in the intake manifold.Looks like I will need to replace the intake manifold.
Expert:  Tan replied 2 years ago.
Ok that the problem water bypassing in the cooling system. If you have water flow bypassing the thermostat it will cause the engine to run cooler as the water flow isn't being restricted. It's like running without a thermostat.
Expert:  Tan replied 2 years ago.
Post back if you have further questions. Please don't forget to positively rate me as that is the only way I get credit for helping you. Thank you.........Tan