Over Heating mystery

[Thompsoncustom]

So I thought I was having issues with my heat sensor so I went and bought a IR thermometer at the advice of a forum member and it turned out to be that the sensor was working fine and the motor was getting to hot.

Replaced the thermostat, head cover gasket and put a new impeller in it and it's still over heating. Looking at the old impeller it seemed to be fine no pieces missing and just hold it's shape a little. Thing is there was some rubber chucks in the top of the water pump housing blocking the hole. Removed them and tested the motor on the river again today and it's still over heating. I'm thinking the water passages are probably gummed up or plugged somewhere. Any advice on the best way to clean all the passages out so I know they are all clear. Is there any other issues that could cause it to over heat that I'm not thinking of? Thanks

 

[oldboat1]

1990 20 hp, right? sounds like the river ate up a prior impeller -- have to clear the bits and pieces (impeller with a set was probably not the cause of the overheating. Keep it for a spare.) If it was mine, I would find a way of flushing the system from the bottom up and the top down. Rig up a low pressure pump system with a fuel hose or similar to fit over the water tube. Remove the l.u. and flush from the bottom first, and see where the water exits -- and that it does. Think you are likely going to want to take off the cylinder head again, and probably the exhaust cover. Pump water up to clean passages, then down from the top.

no easy way. trouble with the bits of rubber is that they can lurk around and cause issues at any point, even if passages appear to be clear. Use a thin fuel hose or similar to carefully run through passages and openings, and try to dislodge debris.

edit. What were the temp readings when it was overheating earlier, and what were they with that recent run (or currently)? It's possible that the current issue is related to t.stat operation -- installation issue, or possible a bad unit. If you pull it apart, test the new t.stat in hot water to make sure it opens properly (should open around 140F -- fully open maybe a little hotter than that. They vary a little.)

 

[Thompsoncustom]

Yes sir its the 1990 20hp and thanks for recommending the IR gun that was well worth the money. Temp reading at the top seem to run 180-190 when the heat sensor kicks in with either tstat installed the difference isn't noticeable.

 

[oldboat1]

yeah, temp guns are good to have. Looking to keep head temp under 160. Sounds like it is indeed a blockage if water is circulating. Might be something that was sucked in at some point, but have to be searching for bits of rubber based on your earlier description.

might have been covered in an earlier thread, but a compression check would be a good idea just to be sure. Then have to try and clear the blockage, unfortunately. :blue:

 

[juno pierrat]

you may need to take the next step, remove the head(not just the cyl. head cover) to look for more pieces, also get new water deflectors

 

[Thompsoncustom]

Hmmm I have a pond pump that I could fit with a hose to try and snake through the passages and flush them out.

Since the motor doesn't seem to over heat at idle or at least I haven't had it idle long enough to cause issues yet any down side to just letting it run in a barrel as long as I keep a eye on the temp? Back flushing seems like it would be the most effective method and something snaked through the passages like a hose or wire.

Something else to note: it seems like if I give it a little gas over idle the pee stream gets stronger but at WOT it seems to be the weakest. Another thing is the very bottom off the head seems to run 30-40 colder probably due to the small amount of water getting through going start to the bottom.

 

[AlTn]

exhaust gases leaking from the head gasket or exhaust cover gaskets can pressurize the cooling system to the extent that water can't circulate properly...advise you to remove the head and inspect the gasket, use a straight edge to check the head itself for warpage, and this will also let you inspect the cooling passages for debris. You'll most likely have to have a new head gasket and head cover gasket at the least.

 

[pro-crastinator]

The symptom of the pee stream getting weaker at higher speed encourages me to think that the obstruction is moving around, and (hopefully) flush-outable.

 

[Thompsoncustom]

I was afraid of that. Head gasket is no big deal as long as the heads not cracked.

I have a compression tester somewhere I need to use that I would think would tell if the head gasket is leaking.

Ran the motor for a hour today in a barrel and the highest reading was 150 so it doesn't over heat at idle or just above idle.

 

[nsa320]

Having the same issue now on my '82 70hp. Can idle and troll all day but about about 5 min after opening it up i get the overheat buzzer. Strong tell tale output.

Finding tiny bits and pieces of the old impeller stuck in the cooling exit hose nylon elbow every now and then. Wondering if a piece is blocking something and not circulating properly, but still getting high pressure elsewhere. Want to pressurize with my garden hose and flush but am worried that any weak exhaust/head gaskets might break and thus flood the engine.

Gonna check the thermostat area tonight. Let me know what you find.

 

[oldboat1]

low pressure for flushing (hose or otherwise), but don't overdue. A lot like pressure testing a lower unit -- 12 to 15psi, or so on a l.u.. Too much, and you blow out seals. With a water flush, it's enough to get a steady flow through the passages.

getting a good result if idling for an hour or so at about 150 degrees. Your motor has an abundance of gaskets, unfortunately, if looking to open it up -- which is the standard fix. One option might be to take kind of a busy ride in it, making periodic checks of head temps (where that temp gun comes in really handy). If you don't have any additional overheating, might have got it handled. I'm not much of a true believer in temp gauges or dependence on tell tales, but in a case like yours a surface temp gauge might be good (i.e., when trying to determine if debris is still lurking in there). Without taking it all apart again, can run it normally and periodically glance at temps if you have a gauge in place.

 

[Thompsoncustom]

Worked on the motor a little more tonight. Pulled the head cover back off and pulled the tstat. Took my garden hose and back flush through the tstat hole. Than put the head cover back on and ran it in a barrel without the tstat installed.

Was getting late when I got on the river but at full speed the pee stream was really strong and it didn't over heat the little I had it on the water. More testing is needed but things are looking good.

 

[oldboat1]

good news. thanks for the come back. want to be a little gentle with the WOT until sure the cooling system is operating right, but just running it can ofter clear it. Got to believe that salt water is more of an issue than river water, but like salty motors it's probably a good idea to flush the motor regularly. Muffs or a hose in a barrel (I prefer the barrel, and keep the hose running -- just idle for 15 minutes or so, keeping an eye on temp.) All good....

 

[nsa320]

No Title

Well, I'm thinking this was my problem. Probably similar to yours Thompson.

Ordered new poppet pressure relief valves. Thermostat looks OK after a good cleaning and test in boiling water. Now to flush those small pieces (old impeller?) out of wherever else they're lurking..