Overheating starboard side of engine

C

Carl

Junior Member
What would cause only one side of an engine to run hot? I have mercury 150hp and the port side runs normal (this side has the temp sensor which sends the signal to the guage). The starboard side runs HOT !! This side houses the sending unit which activates the high temp alarm. I replaced the sensor and sending unit. The temp guage reads normal, but the alarm sounds. I found the the port side felt normally warm to the touch, but the stbd side was so hot that I could barely keep my hand on the head. The water runs well out the telltale.

Any thoughts?

Thanks
 
Thermostat would be my guess. There is a thermostat in each cylinder head in the top of it where the hose connects up at. Also the poppet valve is a big concern with overheating on MERCS as it controls when the t-stats get bypassed to allow for full cooling. The poppet valve is located on the lower stbd side of the engine and is very common for it to get salted up over the years and stick open causing overheating. Normally it will cause it on both sides though. I would start by putting in a set t-stats first and see if that does it. And also make sure the hoses coming off the housings are in good shape with no kinks in them and are free flowing.
 
Thefermanator,

I replaced the soft parts of the poppit valve and ran the engine without t-stats just to see if they were creating the problem. It seems to be happening regardless.

Another crazy thought - could this be an oil issue? The previous merc I had did not have direct oil injection I just premixed. This engine had the oil pump and tank all connected so I left if assembled. Does the oil pump feed the engine between port and starboard or top middle and bottom through the carbs?

Thanks
 
The oil injection is fed through the fuel line before the carbs so all cylinders get the same fuel oil supply. Take the hoses off teh t-stat housings and see if water comes out of them with it running. You may have a plugged hose or a blockage somewhere inside the block.
 
Thanks for the info on the oil injection. I'll check the hoses too. Another question - If there is a blockage in the engine block, would I gain enough access by pulling the cylinder head, or would it require a more invasive disassebly?

Thanks again
 
Most problems with low flow can be traced back to a stuck open poppit valve, but if there is a blockage then yes the heads will have to come off. i've never heard of this kind of problem on the MERCS though.
 
didn't randleman have an issue with his merc, before he went fourstroke? I think the cooling passages were packed full of sand
 
Alright - fast forward almost a month from the last issue. I rebuilt the water pump, replaced t-stats, replaced all the parts of the popit valve and pulled the head just to be sure there was no blockage - (there was not). So I put everything back together and tested it in the yard. Everything seems good. I put it in the water today and let it run at the dock - all seems good. Then - I am running around putting it through the paces and I notice the pee stream falls off and not soon after I get the beep of the overheat. I can quickly get the temp down, buy shifting to neutral and reving the engine over 2k rpm (poppit valve opens) the pee stream is really strong and engine cools right down. This goes on about every 10 minutes or so. I can affect the strength of the pee stream by playing with the tilt of the engine.

My question after all this is: Does this seem like a water pick up issue? The engine runs cool as long it is not moving in the water. Now another issue. - I have a 25" lower unit curruntly on my boat which calls for a 20" motor. I have it bolted as high as it can go, but it is still 2 - 2.5 inches too low. Could this be affecting the water pickup? Would a jack plate fix this issue?

Any ideas are appreciated. I have not done much boating and it is already the end of July.

Thanks


Carl
 
When you had the lower unit off, what did the water tube look like? I have seen a few of them with messed up water feed tubes that would do this. Also retorque all of your head bolts. The longer leg isn't helping you, but shouldn't cause it to lose water unless you are trimming it really high. I know that the V-4 lower unit is known for cavitation issues though as I lost my 140 twice on my 19 angler because it would sometimes quit peeing. Put it on a 19 foot bowrider and had no more problems with it. Make sure you don't have anything under the hull that could be causing it to cavitate like a water pickup or transducer.
 
Ferm,

I retorqued the bolts about a week after I reinstalled the head. I have not rechecked them after I ran it yesterday. I will do that soon. I looked at the water tube for as far as I could see it when I had the lower unit off. This is what I had done when the lower unit off, the t-stats and the poppet valve out, I also removed the plug on the top of the engine and plugged all the holes and filled the engine with water to see where it would come out. It came out the t-stat holes on each side and then I pulled all the plugs and water flowed really steady until the engine drained. i can recheck the tube also. I think you mean the copper tube that is part of the engine and not the plastic extension that comes with a water pump kit. When I was trimming the engine, it never came out the water to disrupt the flow, but it was interesnting as to how it affected the flow. Do you think it could be related to something between the inlet holes of the lower unit and the inlet to the water pump. Would it be worth pulling the water pump housing and seals? Another thought - there is a short hose that is attached to top part on the forward end of the lower unit - I guess it is for speed indication. My previous motor had this hole plugged. Could I be loosing water out that open ended tube that should be going to the engine?



Thanks


Carl
 
put a water pressure gauge on it and report back. When you replaced the water pump, what brand did you use? Did your replace just the impeller or did you replace the housing as well
 
I used the Mercury OEM pump kit replacement included Impeller, gaskets, upper housing, small plastic water tube etc. For the pressure gage, does this get attached at the hole at the top of the engine that has a threaded plug in it?

Thanks

Carl
 
I think I may have found my issue with the water flow on this engine. I was running at 3K rpm and inspecting the engine for any source of water leakage where it shouldn't be. I found water spurting out at the exhaust plate connection - where the power head meets the exhaust tower. It looks like a piece of the gasket is compromised. The higher the rpm, the more water spurts out this spot. Does this sound like the culprit? How hard is to to replace this gasket? I'm assuming the power head has to be lifted?? Annything else I should replace if I separate the powerhead?

Thanks

Carl
 
I think you just found it, the exhaust pressure will get into the cooling passages and prevent water from entering(exhaust pressure greater than water pressure), you will have to pull the power head. The power head bolts(studs) can be a pain
 
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