overheating - looking for a cause

[GKevinR]

1973 chysler 70 hp. started overheating (buzzer going off) when idling. doesnt do it when running down the lake.

Replaced the impeller just because it hadnt been done and i wanted to be sure the key was still there. Reinstalled all that. Ran it in on a hose - alarm went off after about 5-7 mins. let it cool down. Took the head off to check the thermostat. it was nasty but i tested it in a pan of water on the stove. opens fine about 143 like it should.

Running out of stuff to check. Thoughts?

 

[puffitu]

How are (were) your comp #’s?

 

[Sea Rider]

Fresh or satr water use ? That's a 47 year oldie. Removed the cylinder head or just a lid/cap to check the thermo conition ?

Happy Boating

 

[GKevinR]

Compression is good. I've pulled the head. Freshwater run only. Isn't there a different cover I need to pull where the water first comes into the block?

 

[The Force power]

1973 chysler 70 hp. started overheating (buzzer going off) when idling. doesnt do it when running down the lake.

Replaced the impeller just because it hadnt been done and i wanted to be sure the key was still there. Reinstalled all that. Ran it in on a hose - alarm went off after about 5-7 mins. let it cool down. Took the head off to check the thermostat. it was nasty but i tested it in a pan of water on the stove. opens fine about 143 like it should.

Running out of stuff to check. Thoughts?

You may of (inadvertently) not insert the pick-up tube into the water pump housing?
Just drop the LU slightly and see if the tube is lined up with the pump
Does it have a tell-tail?

 

[jerryjerry05]

You changed the impeller, now it overheats?
You sure it's the right impeller?
47 years old and the sending unit might be faulty?
Get a heat gun and check the temps all over the motor
and verify the motor is really getting hot??
The thermo opens at 143 the sensor doesn't work until
it's closer to 165/170

 

[Sea Rider]

Some issues :

If the thermo was found at a very nasty condition, imagine all the internal powerhead's water passages condition which could be similar and already narrowed after 47 years of constant use, that's motor not dissipating heat well and not cooling as it should.

Will need to troubleshoot the temp sensor as well if triggering at the correct temp or already shot, the procedure must be stated on the Service Manual. Nope it's not similar to boiling water as when testing a thermo, it's more complex...

If that motor were mine would clean "all internal water passages" to factory condition, install a new thermo and heat sensor and test the motor at open throttle on the lake...

Happy Boating​

 

[GKevinR]

motor started overheating before I changed anything. only time it seems to do it is at idle. if you are wide open down the lake, no issue. i did change the impeller and used the exact same style as came out of it (which wasnt in bad shape to begin with). I have ordered a new thermostat, thermo gasket and head gasket. I can order a new thermo switch. I did verify the water tube was in the rubber cup on the pump.

on some other internet threads, people were telling how they pulled another cover to get to the area that the pump fills before the water goes to the thermo and into the head. on my engine, i'm guessing that area is just to the left under a big rectangular flat plate. looks like it also has a gasket that will need to replaced if I pull it.

its odd that it started on a motor that has been perfectly fine and doesnt seem to have needed an impeller or thermostat change. only at idle when the pump is spinning slowest.

 

[GKevinR]

does this motor have a poppet valve?

 

[Sea Rider]

Would be ideal to get the Parts Manual for that model and check all the water related covers the powerhead works with, if having a poppet valve ? Will know which parts to remove and clean. Good to order a new thermo switch.​

Happy Boating​

 

[GKevinR]

I have a manual. Saw no mention of a poppet valve but wanted to check. Manual doesn't go into troubleshooting very much.

 

[topgun3690]

That flat rectangular plate is the exhaust port cover. Look for a small oval shaped cover near the bottom left corner of that cover that has 2 small bolts holding it on. If you have one, the poppet or "relief" valve is inside. It only works at high rpm's for pressure relief, so don't think it would effect idling temps. What manual do you have?

 

[GKevinR]

chrysler outboard service manual for 3 and 4 cylinder outboards for manualib.com. looks like the original service manual.

 

[GKevinR]

i know its not peeing out the pee hole. i'm really sure the impeller and tube is all good. once it leaves the tube, where does it go? maybe a blockage? i doubt this motors water passages have ever been cleaned out.

 

[topgun3690]

Check back here EARLY in the morning.....JerryJerry will probably chime in with more info.

 

[jerryjerry05]

The poppet shouldn't make a difference in overheating.
They stopped using them on Forces after 89/90
IF? the thermo had crud on it then the cooling passages could be clogged??
The heat gun will tell if there are hot spots.
Or remove the head and check the passages??

 

[puffitu]

As guys are stating; the heat gun can tell a lot and in my case my thermo switch was ok but the wire to it was rubbing and making contact at idle after warm up; when everything was nice a warmed up. At wot it would fall away so no issues there so much. I’m not familiar with your model but sounds like 1) blockage 2) thermo stat related
Good luck

 

[Sea Rider]

Does that model have a flushing port built in the crankcase, if so remove thermo, put cap back on and flush with water at high pressure. Could use a Karcher washing machine set at min pressure for that task.​

​

Or remove the lower leg and use high water pressure or high air pressure connected to the water pick-up tube with removed thermo as well.​

​

Happy Boating​

 

[jerryjerry05]

Forces don't have the flushing port.
IF?? the cooling passages are clogged???
NO amount of flushing will clear them.
The sediment gets realllllly hard and only a screwdriver
or something similar will get it cleared out.

One of my customers had a 40Yam on a toon.
I
Being as it was on the dock and didn't ever get flushed
it was really clogged.
I removed the head and the sediment level was 2/3 of
the way up the 3 cylinders.
It never showed hot because the thermo switch was up
in the section that still had flow.
The pics show the thermo that was in there.
Luckily it was frozen open.

 

[Sea Rider]

If a motor overheats not necessarily means that all water passages will be found clogged. What really happens is that with time and use all the water passages begins to collect thin salt layers one on top of the other that will eventually decrease the water passages diameters due to being porous, repetedly ON-OFF heating cooling cycles, motors badly or not flushed at all and the salt % contents which varies from ocean to ocean. More on the equator, less on other latitudes.​

Motors used in fresh water will tend to collect lime, calcium and other particles on the entire water passages as well, the positive issue is the motor will take way much longer to overheat compared to a motor used on salt water which has collected huge salt layers inside the entire powerhead.​

In both particular cases will need to remove cylinder head, exhaut covers and crankcase from base, scrape manually all water passages with plastic or wooden tools as not to scrape the water passages with sharp, pointy metal tools. If so, with time will tend to collect salt layers faster compared to smoother water passages.​

Install new gaskets along a thermo as well, go for a wot run for 15 minutes, the motor should cool and run exceptional well as when factory delivered provided the temp sensor is in good working shape as not to trigger itself prematurely at lower temperature. Extremely salted water passages will take much longer to dissipate heated water inside the powerhead and cool the motor more efficiently compared to clean ones.​

The worst motor scenario is the one that's used in salt water living behind a boat and never flushed with fresh water after use. Those will achieve excessive overheating issues when the boat is on plane and running at medium to full wot rpm range for long time periods. In such case expect to find a Pandora Motor when opening them..​

Until the engines don't run on coolant like in cars expect to have overheating issues in the medium and long term...​

Happy Boating​