Marinette Boat Forum

I encountered an issue of my 1984 Chrysler 318 Stb engine temperature spiking end of last year and now more frequently today on our maiden 2019 voyage. I’ll be going along fine around 160 Degrees and suddenly the gauge rises to 200+. Typically it corrects itself after slow down. Sometimes, a bit of increased rpm will “clear it up” and temp falls back to normal. Intermittently the spike comes back again . I’ve replaced T-stat and Raw water impeller this past winter. I’ve never realized any performance issues but I never let it go too long at high temp. I’m hoping just the gauge. FYI, port engine was consistent at 150-160 the entire time. Also, confirmed reading on the Upper & lower gauge. Otherwise, a good launch and nice ride dodging walleye fisherman in the Channel

clogged manifold? clogged heat exchanger? air leak in strainer w/corresponding drop in flow? Also possible new t stat is faulty. I think I had the same problem and am wracking brain to recall what resolved it (if it ever got resolved).

Might just be a bad temp sender unit or connection/ short.


Suggest regular checking of the actual motor temperature with an infrared temp gun. I never leave the slip without one! Put the red dot on the metal shell of the sender unit.

Jeff

Thank you, Joel & Jeff. @fastjeff, where is the sender unit likely located on my STB engine? -thx, Joe

In front of the manifold, near the t-stat housing. The one you're looking for has one wire going to it--the temp switches have two wires.

Jeff

Had same problem a few years back... turned out sucking air at the strainer. Was ok at idle then loss of flow at higher rpms.

Often the leak is the O ring on the center bolt of the strainer lid.

Agreed! Thanks for reminding me.

The crappy square "o-ring' was the culprit. Replaced it with an o-ring made from joining a length of vacuum tube together and never had that problem again.

Jeff

I too had the same issue where suddenly the temperature would spike and then correct itself at random intervals. Mine turned out to be the strainer as well. I watched the volume of water going through one strainer (the problem one) seemed less than the engine strainer with no issues. I tightened down the nut on top of the strainer more and noticed an immediate increased water flow in the strainer. Turned out mine was sucking air as well. Problem solved - no more temperature spikes. I credit an earlier post on this topic from FastJeff I think in guiding me to it.

Ray/Jeff, very interesting. I noticed a seeming lack of flow in both strainers upon initial launch. Port was humming like a teapot last year, now both were streaming into to strainer at a “dull” pace. Although the temp issue again was on the STB only. I’ll start with the easy stuff and replace the strainer gaskets as needed and see if there’s any progress. Thanks again

OK "air leak in strainer" was my #2 possible culprit in my May 3 reply (above)...it should have been #1 because it's the easiest to check and a prime offender as others agree. They're cheap - I got replacements (I'm pretty sure) from Buck Algonquin which is still in business.
For a quick verification check. Take the gasket from strainer #1 and add it to strainer # 2 and see if the flow improves. Another thing I recall doing successfully once was to flip the gasket over and change its seated position. That improved the flow but the gasket were replaced anyway.