1986 Johnson 150 V6 Cooling & Cylinder Head Temperature Model #J150TXCDC

[Terrapin]

I installed a new water pump kit, new thermostats, new pressure relief valves, and related seals. I did not replace the pressure release valve seat.
I fired the motor up on the trailer at a local ramp, but I can?t run in the shallow water at this location. I now have a strong telltale and 6 psi at idle per my pressure gauge. I read the cylinder head wall temperatures with a Fluke infrared gun. The approximate temperatures were as follows:

Left/Port Head:
120 degree F at idle/800 RPM
110 degree F at 1500 RPM

Right/Starboard Head:
100 degree F at idle/800 RPM
85 degree F at 1500 RPM

Immediately, upon initial start up, the starboard head read 90 degree F. The port head was reading 195 degree F, but then dropped down to 95 degree F. Was this due to an air lock?
Shouldn?t my port and starboard cylinder head temperatures be more similar in temperature reading at idle? Shouldn?t the temperatures be at 145 to 155 degree F?

 

[emdsapmgr]

Normally the head temps would be I the 145-155 degree range at idle. That's when you are in a warm lake-floating normally in the summer. Late August timeframe. Water temps maybe 75+ degrees. I've seen similar 100-120 degrees if you are on a cold garden hose, or if the lake temps are cold, such a springtime temps when the water is under 40 degrees. Cold (springtime) lake temps won't let it warm up to the "normal" idle temps. That's ok. Now, once you crack the throttle from idle or once you get up on plane, the pressure relief valves open inside the stat housing. When that happens tons of extra cooling water flow thru the powerhead. Normal for the temps to go down 20 or more degrees from idle temps. In the early spring, my cyl head temp gauge goes off the scale, down below the 100 mark. All normal. The cyl head temps will be close, but one will run cooler due to the circulation pattern designed into the block.

 

[Terrapin]

Thanks for your quick reply. I stopped by the boat ramp this morning and measured the river water temperature to further understand this situation. The water temperature is currently 68 degree F. Would this water temp be low enough to explain 100 to 120 degree cylinder head temps at idle? Thanks!

 

[emdsapmgr]

800 sounds high for idle. Maybe it's just in neutral. Try putting it in gear and let if run for a few minutes at idle-in gear, then check the temps again. Usually idle rpm's are in the 650-700 range- In gear. It still sounds as if everything is in the "normal" range. Sorry for the double post-the website is really crawling and it's hard to know what responses have actually been transmitted.

 

[emdsapmgr]

800 sounds high for idle. Maybe it's just in neutral. Try putting it in gear and let if run for a few minutes at idle-in gear, then check the temps again. Usually idle rpm's are in the 650-700 range- In gear. It still sounds as if everything is in the "normal" range.

 

[Terrapin]

Emdsapmgr, thanks for your replies. Prior to replacing the water pump, the overheat alarm went off and I was forced to pull the thermostats to keep the alarm from sounding. The water pressure at idle was lower at 2 to 4 psi. It seems the new water pump kit improved water pressure significantly to allow me to reinstall the thermostats. Testimony that one must replace the water pump at a regular 3 year intervals. I?ll report back when I am able to run it at higher RPMs.
I?m still a bit concerned with the condition of the water deflectors given the age of this engine. I would replace them as a preventive measure, but I am a bit concerned with snapping a cylinder head bolt upon removal. Are there any tricks I can use to avoid cylinder head removal problems?

 

[emdsapmgr]

The head bolts are pretty robust. It is always possible one would snap, but I'd think it's more likely on a saltwater engine. Usually the bolts that snap are the smaller 1/4" bolts on the head covers. I'd be more concerned about the position of the deflectors if you had any signs of overheating. That does not appear to be your problem from your readings.