150hp Temp

[25whaler]

Hope everyone enjoyed the Holidays. I have twin 150 johnsons (1986) recently installed temp gauges. I have installed a sending unit on each head and a toggle switch to go back and forth between port/stbd on each motor. This weekend was the first run with it. The heads (all 4) idle at 140 degrees but when I run the temp drops down to 80 or 90. T stats are all new this year. My question is ... is this normal? I thought the t stats were supposed to keep the temp around the 140 range. I am worried of carbon build up at low temp also could the water be blowing past the t stat at the poppet valves?? if so what is the remedy? Thought it was weird that all 4 were doing this if it was not normal Thanks

 

[walleyehed]

Re: 150hp Temp

Not sure on your year model, but some had a bypass valve to allow extra water flow at higher than Idle RPM (mid-range-up).<br />This would be a good one for Dhadley to look at.

 

[Dhadley]

Re: 150hp Temp

Where are you reading the temp at exactly?<br /><br />Are the pop off valves in place with the correct springs? T-stats in?

 

[OBJ]

Re: 150hp Temp

Sounds a little cool to me. I'd be interested in the answers to Dhadleys' questions to...

 

[25whaler]

Re: 150hp Temp

Thansk for the replys guys. I appreciate it. I am reading the temp on the gauges that I have installed on the dash. Farie set with cylinder head sending units. I realize they may not be exactly the most accurate but the swing from 140 to 80 I felt was alot. Springs are correct also t-stats. Pop off valves are in place as far as I can tell.

 

[OBJ]

Re: 150hp Temp

Whaler....I think what Dhadley wants to know is, where are the temp sensors mounted. Which part of the head are they mounted on.<br /><br />Can you give us a year or model number of your engine please?

 

[25whaler]

Re: 150hp Temp

Sorry. They are 1986 150hp johnsons. I have mounted the sending units just below the tstat housing. They are as high up as i can mount to a flat surface. They are held in place with a cylinder head bolt. Not the bolts that actually hold the cyl head to the block but the water jacket (its right near the sparkplug hole) I can try to take a picture if needed

 

[Dhadley]

Re: 150hp Temp

OK. Try to relocate the sensor to near where the temp senders are located. They are the sensors under that plate with a wire connector.<br /><br />Make sure the t-stats are in and the pop off valves are in place.

 

[25whaler]

Re: 150hp Temp

Dhadley, The senders are about 1 inch from the oem sendor (brwn lead). Do you think its possible that all pop off valves are not seated?? . Tstats were replaced at the begining of the summer. I am stumped. The only thing I can think is the pressure builds and causes water to go thru valves?? I took a pix of location of sending unit but having trouble posting

 

[Dhadley]

Re: 150hp Temp

If the t-stats are in and working properly make sure the edge of the pop off diaphram is seated in the groove in the head. Also make sure the grommet is in place. <br /><br />The other thing is to verify the temps. Its best to use a heat reading type gun like a Ray Tec. We're assuming the gauges are reading correctly which they may not be.

 

[seahorse5]

Re: 150hp Temp

Your engine has the spring loaded diaphragms and white "pop off" or pressure relief valves. The thermostats keep the cylinder heads between 125 and 160 degress ( 145 plus or minus 15 ). Above around 1800 rpm, the water pressure lifts the "pop off" valves and water flows directly thru the block and the coolent temp drops to around 25 degrees above the water inlet temperature.

 

[25whaler]

Re: 150hp Temp

seahorse, thanks for your input. I think thats what is going on. That would account for the readings i am getting as water temp was 60-65 and my temp was reading 90's. Thanks to everyone for your help.