Cooling system mystery

[Buttanic]

It's Mercruiser 260 with closed cooling and was rebuilt 5 years ago with new manifolds and elbows and an Edelbrock aluminum intake manifold. Have not had any problems until now. It has a 160 degree thermostat. I have a temperature gauge mounted on the left side of the cooling water cross over of the intake manifold and an adjustable temp alarm mounted on the right side of the crossover.
I stared it up and it was idling when I noticed the temperature gauge was up to 190 but the alarm had not sounded. I started turning the alarm point down and it went off at about 140 degrees. Didn't make sense. I started checking temperatures with a hand held infared temp gun.
The right side head was running at 140 and the left was 200. All other locations on the manifolds were between 125 and 140 except the left head. I pulled the thermostat housing and the thermostat appeared to be fully open. I remove it and started it up again and the left head was running back to normal.

I did this twice and each time with the thermostat in place the left head over heats but runs normal without it.

It's got me baffled.

 

[makonnen]

Re: Cooling system mystery

Well I can't explain the 160 T-stat and 190 temp but an engine running at 190 sounds about right to me. Cars these days run 220+ but boats have always been slightly less for some reason. Lower temp is not better, you need the heat so the metal parts can expand and take up the freeplay and for fuel to properly atomize and not condense on the cylinder walls.

As for the discrepancy between the two heads ... one of my elbows runs a whole lot warmer than the other one. Ie: one it slighly hot to the touch while the other one is in the comfy zone. I would think this is weird but I have two boats and they both do the same thing.

How exactly are you measuring the temp of the head and why do you think this is what the coolant temp is?

 

[LX Kid]

Re: Cooling system mystery

Try removing the thermostat and put in pan of boiling water. Make sure it fully opens at 160. Make sure hoses are in good condition. Sometimes when they get a little wear or they are not marine grade hoses they could possibly get an air bubble inside the hose and restrict flow in hoses when hot. If the block and heads wern't chemically boiled out they could have some scale that broke off and sealing some passages. Just a few things to think about. Good luck and let us know what you find.

I had same proplem, kinda, with mine and removed my risers and they were plugged up good. I chipped away at all the riser passages until they were clean. I then knocked the center out of my thermostat and it's been running about 140 for the past two years.

 

[Buttanic]

Re: Cooling system mystery

On this engines risers are raw water cooled, manifolds are fresh water cooled. Every year I check all my engine, manifolds and riser temps with my infred temperature gun. Everything was always even within a couple of degrees on both sides. Even if the thermostat wasn't opening all the way both sides should be equally hot, not one cool and the other hot. It is only the left head that has the high temperature with the thermostat in place. I have good water flow out the exhaust on both sides.

 

[Buttanic]

Re: Cooling system mystery

Installed new 160 degree thermostat. Left head still overheats, right head cool. Removed circulating water pump and flushed left bank with a garden hose in the water pump discharge hole in the block and get good water flow out the thermostat housing.
Will try again once it get it back together.

 

[Oshkosh1]

Re: Cooling system mystery

Remove the thermostat and run it...see what number you come up with.

I don't know why you NEED a T-stat in many of these engines. Because they operate most of their life around WOT in relitively warm water, heating the engine up to operating temp is not a problem(just idiling at the dock for a couple of minutes does it). Add to that the consequences of the failure of a $5 part in the middle of a lake on a hot July day, and I don't see the need.

I don't run T-stats in my snowmobiles either. I've had one stick closed and ruin a motor on a trail...never again!