1990 SN - Heating

[Daryl]

here is the scenario, 1990 SN, PCM351, checked strainer and impeller (new at beginning of season), both appear fine.

boat heats - gets up to almost 200 degrees at idle after working for a few sets - seems to cool when I run up the speed but also appears to be getting worse.

haven't done any water volume testing yet.

Next thing i'm going to check is hose from through-hull to raw water pump for blockage.

Anyone offer any more tips or share their experience?

Also - how hot is too hot? is 200 degrees pushing it or not a big deal?

[skinautique]

200 hundred degrees is too hot. You should be running around 140 to 150 with that engine. Stop running the boat until you figure out the problem or you will do worse damage. It could be a number of things. Loose hose sucking air, bad exhaust, bad guage or maybe a thermostat but I kind of doubt that one. Let us know what you find out.

[M3Fan]

200 is way over. Could be a stuck thermostat, or you are sucking in air somewhere. Swap out the 'stat.

[xlair]

Almost all overheat issues in inboard boats are due to impeller and/or waterpump housing failures. Use only PCM OEM impellers, never aftermarket, they are not always the right dimensions. Always check the water pump housing and plate the impeller rides on for scoring. Reverse the plate if necessary. make sure the pump is not running backwards, the drain hole should be facing towards the inside of the engine, verify by how the paint is sprayed (bottom and inside are lightly painted). Pull the hose off the top of the w/p to verify water coming thru (or at the thermostat housing. Make sure transmission cooler is not plugged and water strainer oring is intake. Look for cracking in the water strainer bowl that would allow air in. If your original impeller fell apart, look for the pieces in the lower hose, flush out with a garden hose. These pieces often get caught in the w/p intake and then fall back so you don't see them. Good Luck.

[xlair]

Also, don't assume the impeller is good because it looks OK. The vanes must be strong enough to press against the sides of the housing. The w/p works hardest at idle. Often worn impellers work ok at high speed and not at idle. Replace if at all in question. Remember to check the housing.

[UWSkier]

Agree with M3. Thermostats are cheap. Try a different one.

[M3Fan]

To see if it is the Tstat, you could run it briefly in the driveway with the hose connected and see if you have water flowing out your exhaust. If you do, and it still goes past 160 (obviously don't let it go too far past) then it's probably the T stat. Not the greatest technique, but a no-brainer.

[efox]

I have a 92 and the guys at discount Inboard suggested I run a 165 deg Tstat rather that the 140 that originally came on the boat. It too runs about 180, but I noticed that when running with the nav lights, stereo, and auto bilge, the guage hits 200. I think your problem, and mine too, might be electrical. I plan on pulling the guage to check the ground and then changing the guage if needed. I also noticed that the amps were in the 10a range on the guages when all this is going on. The other thing I would suggest is to see how hot the engine "feels". If the your temp is over 200, there would be now way you could get your hand on or near the manifolds or rocker covers.

Eric Fox

[Daryl]

well... finally got the boat back in the water today..

still heating.

but here is what i found.

the strainer glass had some small cracks - i put two part epoxy on them to see if that was the problem - it might still be getting air there but I thought that was it.

also - the fitting on one end of the strainer was lose (the up-lake side) tightened that too.

I thought those two things were the ticket.

just heats at low rpm (say less that 1000) after that all cools right down.

so - when I got home i starting looking around some more. and found a loose hose clamp on the engine side of the raw water pump. (so I asume that can't be a source of air)

I tightened all the hose clamps on the water line circuit...

next step is to get NEW water strainer glass, and try and run without thermostat.

might also order new impeller - can't hurt to have a back-up anyway. (impeller was new this season)

so - the quest continues... Thanks for everyone's feedback - i'm looking into everything - just one step at a time.

[skinautique]

DO NOT run that boat without a thermostat in there. You will be very sorry later on. Get a 143 degree thermostat. The water strainer bowl definately needs to be replaced. Check every last one of your hose clamps all the way down to where the water comes through the hull. You are doing more damage inside the engine then you realize when you run them hot. You can fry your exhaust system in a heart beat.

[Daryl]

thanks for the input skinautique.

don't worry... i'm not running the engine hot - just poped it in the water to see what is happening - really thought I had it fixed....

the qauge has never gotten above 200 degrees, if it gets hot, i simply run the boat up to speed to cool it down and then shut it down.

I've only ran the boat once (that was today) since the problem arose...

tomorrow - i've got the big man - MY DAD coming to help - we will get to the bottom of it for sure tomorrow - i'll report back!

[siuski]

Like Xlair said, check the o-ring on the water strainer, if unseated, warped, etc. it will suck air.

[Daryl]

well... had boat on water tonight, looks like the thermostat is the culprit.... now the question....

what is the right thermostat for the 1990 PCM 351?

it has a 142 inscribed on this one.

SKIDIM looks to have a 143, 160, 170

I'm thinking of running a 160 - any comments?

Daryl

[skinautique]

run the 143 unless it has a heater. if it has a heater, run the 160. glad to hear that you found your problem.

[Jr]

You should run a 160 degree thermostat. your problem might be the seal and bearing in the front of the pump is bad. I have replaced a lot of pumps over my 13 years in working at a correct craft dealer.