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Temp gauge question

D

dock_holiday

Contributing Member
"Hi all. The temp gauge on my

"Hi all. The temp gauge on my 1972 AQ 170 is the VP one with a green arc with a red wedge at the "hot" end of the arc on the face of the gauge. If you have seen one you will know what I mean. If not I am sorry for the poor descrition!. There are no numbers to on the face at all. Anyway, when I run the boat with no thermostat the needle on the gauge never gets higher than about 1/4 up the green section of the arc. With the thermostat in it will run up into the start of the red real quickly if I am running it at high revs or working it hard. This is the area on the arc where the needle covers some green and some red. If I don't take action to lower the temp the needle will climb right on up into the middle of the red section (very scary!) I can get it to go back down into the green if I hold it at a high idle like 2000 RPM for a minute or so. I know the impeller and the circulating pump are good. I just looked at both of them, and the fact that w/o the thermostat the gauge shows nice and cool tells me the pumps are working. There seems to be a delay in the cooling effect... the needle goes to the hot end of the arc faster than it goes back down. I suspect at I have either a bad gauge or a bad sender, or a bad thermostat. I know the thermostat opens and closes because I put it in hot water and watched it do so before putting it back in the motor. Maybe i have the thermostat in upside down? I installed it the way it was when i took it all apart. what would be the symptoms of a thermostat installed upside down? Anybody have any thoughts on where to start with this? --- or should I just pull the thermostat and run without it? (I am guessing El P. says no to that idea) LOL.

Thanks in advance, and sorry for the long post--trying to be thorough.

Matt"
 
"Buy/borrow a heat gun and get

"Buy/borrow a heat gun and get a reading of the real temp of Your engine.
If the engine is fresh water cooled, it should run close to the red, if raw water cooled about 2/3 up on the green.(Different thermostats). Instrument reading might change over time as resistance increase in harnesses. Check that water outlet in raiser is not restricted by corrosion."
 
How is the hose connector in t

How is the hose connector in the outdrive? Is it corroded/perforated? And how are the exhaust manifold and the oil cooler? Hopefully not plugged-up with mud and scale.
 
"Morten, the heat gun sounds l

"Morten, the heat gun sounds like a real good idea. Thanks. The motor is raw water cooled. I am not sure what you mean by "water outlet in raiser" Do you mean the short copper pipes that carry water to and from the thermostat housing? If so, mine are good. I have not seen any corrosion or scale anywhere.

El, I have looked at the hose fitting coming out of the outdrive, but I will give it another look, more closely. The exh. manifold looked fine when I had it off to replace head. The oil cooler is an unknown. I could pull it off and look. The fact that the cooling system moves sufficient raw water through the head for the gauge to register way on the cool end when I have the thermostat removed suggest to me that water flow from the leg on up to the motor and through both pumps is not the problem. If the pumps or tubes were bad taking the thermostat out would make no difference right? or am I missing something? I think either the thermostat is not installed correctly or is not functioning correctly and as a result the head gets hot; or on the other hand the head is not really getting too hot and the gauge/sender system is not functioning properly (reading too hot).

Thanks again for all the help! I have got some new things to investigate.

By the way, this has nothing to do with the new head-- the motor acted the same way with the old head on. I am using the old thermostat.

Thanks again.

Matt"
 
buy a new thermostat then try

buy a new thermostat then try again becacse you know the price of those heads as do i $$$ auto store has them for a 1974 volvo 164
 
"John, I'll pick up a new

"John, I'll pick up a new one. Is the temp range for the AQ 170 the same as for the 164 car motor? I understand that a car one will fit physically, but I want to make sure I get one that operates at the correct temp. range for the marine application.


Matt"
 
"The opening temp for the raw

"The opening temp for the raw water cooled is less than for the dual circuit cooling and cars. Even if You run in fresh water, the car thermostat may not be used as You will need a pressurized system to make it work properly."
 
"Matt, Seloc calls for a 127ºF

"Matt, Seloc calls for a 127ºF-133ºF thermostat, which should be fully open at 151ºF-158ºF. I would follow that spec."
 
"There is another item that mi

"There is another item that might cause 'problem' and that is the circulation pump. When You get the heat gun (?), I suggest You check around the block all the way to be sure the temperature is balanced. A worn pump might cause bad circulation and at higher revs not circulating properly and cause overheat. It might pay off to check the clearance between pump impeller and housing as well as cavitation damage on impeller."
 
"Morton, El P., thanks for al

"Morton, El P., thanks for all the great info on this issue. The proper temp. range info provided by EL P. is interesting becuse as I recall there is a "165" stamped into the metal on the thermostat I am currently running (it came with the boat when I bought it.) I think someone might have put a car thermostat with too high an opening temp. in there. If so, I think it would explian 100% of the problem I am having. I will pull that thing out and have a look at it as soon as I have time. If it is a 165 deg. thermostat I will buy a new one as per EL P.'s suggested heat range and go from there. If that fixes it I won't have to mess with the heat gun.... might be kinda cool to play around with one anyway...

Thanks again guys!

Matt"
 
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