Temp guage reads 200-220 '90 SN 351 but motor not hot???

[linebacker55]

I would check thermostat as well. It is a cheap and easy part to replace, and you can test it in a pan of boiling water to see if it opens or not, and you can run the engine without it and see if it heats up. If it doesn't, there is your problem.

[MiracleDriver]

I want to, but it is being a real SOB. I even used my power drill and no go....

will try a little liquid wrench..

would it really be the thermostat, I'm leaning towards the pump or a blockage somewhere because of these symptoms:

the motor runs fine at idle and up to cruising speeds around 30mph, but once you give it more gas 35-40+ mph it jumps up over 190. I back it off to neutral and it comes down to 180+. then I put it back in gear and 10-20mph before plane and it drops to 160.

If I get it off and it is working, I suppose testing the RWP and circ pump is the next step.

any other insight? thanks so far guys. will post an update

[MiracleDriver]

had it out again after pulling the hoses. I can't get the **** bolts out to pull the thermostat. theoretically they should be easier to pull when hot right? I've gotta find a tool to pull it.

that said. I still don't think its the thermostat because the boat runs fine up until around mid 30's mph. I see this as being a pump issue.

I then inspected all of the hoses again, the strainer again. and noticed that I had a pin sized leak in the intake hose that attaches to the tranny cooler. could this leak cause the overheat that I am now describing? its the only leak anywhere.

[linebacker55]

Just a thought...has the impeller been replaced since last season? If so, maybe the wrong one got installed, and it is slightly too small, and pumps some water, but doesn't get a great suction? A pinhole leak probably isn't going to cause this kind of a cooling issue. Has this boat ever had a bad impeller since you have owned it? It could be there is a piece of impeller stuck somewhere, but you would think it would have had these problems before now...sorry i can't be more help.

[MiracleDriver]

it has never had a bad impeller. I run in crystal clear glacier water, no weeds or sand either. it is in mint shape and we have never had a problem in 5 years owning the boat. it has never overheated before this season.

if the impeller is okay and the pumps aren't leaking can they even be causing the problem?

what about a restriction in the risers? there was rust in them when we went to put the drain plugs back in. any way to check or clean them out without pulling them?

thanks so far

[linebacker55]

I don't think a little rust is the problem, either. If i remember right, the flow of water splits at the thermostat. When engine is cold, thermostat is shut, all water bypasses engine and goes through exhaust. As engine heats up, thermostat opens and allows cooling water in. The thermostat could be only opening partially, or stuck in a partially open position, therefore at lower engine loading, it has sufficient cooling capacity, but as you increase the load on the engine, it doesn't allow enough water in to cool the block. I know this sucks, as you can't get the thermostat off, but that is what this points to from my perspective.

[MiracleDriver]

Thanks dude. I sent an email to Vince at skiDIM and he said that my boat came with a 143 thermostat. I am going to order a 160 as well, just in case.

I have read that they like to operate at 20 degrees above the thermostat range. he also mentioned that maybe the housing is shot because an automotive thermostat was used in the past. I've had the boat for 5 years and never opened it so I have no idea.

going to use a little liquid wrench on it and hopefully it loosens it enough that we can get the bolts out.

I am leaning towards the thermostat as well. thanks everyone for all your help.

I will post an update once I get a new thermostat in.

[MiracleDriver]

got the old thermostat out using liquid wrench.

put the new one in, but haven't been able to get the boat in the water yet.

I put the old thermostat in a pot and it opened, when I pull it out it closed. any pictures anywhere of thermostat's open and closed?

now I don't know where to look.

I am getting water, the thermostat housing is cool, as are the risers and you can feel the water pressure.

I checked the sender as described and it seems to work, my gauge seems to work and my impeller looks perfect.

it doesn't overheat past 180 unless you are going over 36 mph. with the nose in the air it seems to keep under 170 and it doesn't overheat over 170-180 at idle.

this all started when I forgot to put the water strainer gasket in. when I put it back in I get the temps described above.

I guess I have to check the pumps.. grrr

[MiracleDriver]

put the new thermostat in as mentioned. it proceeded to run it off the garden hose and it overheated with the new one in.

so I checked the circ pump by pulling the block drain out and it shot water out. no probs with the circ pump.

I pulled the hose from the rwp and it shoots water out.

I then pulled the new thermostat to run it without one.

the temp was showing 160 on the gauge before I started it. It proceeded to drop down to just over 150 and held there.

I am assuming my new thermostat is no good as well and that was my problem.

However, I've tested the old thermostat and the new thermostat on a pot of water and they both open about 1/4 of an inch. the new one looks to open more and also seemed to open a bit later than the old one.

both are 142 pcm thermostats.

could they both be opening too late and not enough?

as mentioned the temps stays at 152 on the gauge without a thermostat in...

[MiracleDriver]

bought an infrared thermometer for $50 at princess auto (on sale).

temp never went above 141 on the gun.. dash showed 180-190+.

thanks for all your help guys.

even though I went over the gauge and sender using skiDIM's faq and talking to my mechanic who thought they were acting normally. both the pressure gauges read high...


thanks again!
MD

[linebacker55]

I am glad you figured it out.