143 Thermostat question

I"m working on an overheating problem on my '88 2001 with a 351 PCM. After changing the impeller, cleaning the water filter and inspecting for blockages I changed the thermostat today (a 143 thermostat). There was no difference in the temperature with the new thermostat. It idles at 180, runs 175 at wakeboard speeds and 185 at slalom speeds.

I think my ultimate problem is the RWP as it takes about a minute to run suck a 5 gallon bucket dry from the water intake hose. However, before dropping the money on a RWP I decided to test the thermostat on the stove.

I put the new and old thermostats in a pot of water and slowly heated it up. They both opened at about 155 just a crack then fully opened about 160. When they were cooled they closed around 140. Is this how a 143 thermostat is supposed to perform? I was under the impression that it should open up at 143. I did this several times with the same result each time from both thermostats.

My 1978 351W we ran for many years. Sold it with 1,500 hours on the clock.
It ran right at 140 on the gauge all the time and we used to barefoot a lot behind that boat.
Any time it ran hotter than 140 I knew I had a problem, I would search and fix that problem and get back to 140 temps again. Feed a garden hose into your intake and run the engine.
If it stays at 140 you have a supply issue.   Common supply issue is an air leak on the intake side between the pump and the intake.   An old hose or a loose clamp can allow air to suck into the system. If air is sucked in you will not have vacuum to supply your water to the engine.
The hoses may be old and stiff.   Tighten them when they are warm. You will never get them tight while they are cold. An air leak can be at any connection between the water intake and your water pump.   Did you install a quality impeller?   Some brands out there don't work even when brand new.
Hope this helps.
Mark

When you changed impeller, how did the wear plate inside pump look?.

If grooved badly, you can flip it over & use the other side.

Good luck.

The wear plate looked good. I didn't look at the cam or shaft seal. Am I just looking for signs of wear on those? If those are worn am I looking at a RWP rebuild or replace? I'm a novice so depending on the difficulty I'm not sure I can rebuild it.

The impeller was a Sherwood from Christie's Marine, same type I've been using for 10 years without any problems.

There is a gasket on the water strainers on the intake side. I had one of those leaking air, did not leak water out but air sucked in.
Trace the intake lines from the bottom of your boat all the way to the Raw Water Pump.
It may go to the water strainer, then the oil cooler and then to the Raw Water Pump.
Any air leak along the line could be your cause of high temp.
I never had to change the RWP seals so can't advise on that.

I've checked every connection between the intake and RWP. Everything looks good from what I can tell. The water strainer O-ring looks good but I'll go ahead and replace just in case.

It sounds like my problem is a little different than yours. I run 180 pretty much all the time from idle to wakeboard speeds. It runs 185 for slalom and hotter during barefoot runs. Letting it idle will bring it back down to 180 but it never gets cooler than that while running.

Another thought - Maybe it isn't getting as hot as the gauge says?

You could use an IR thermometer to check actual temp.

Pete, if he disconnected the hose from the bottom of the boat at the intake and put it in a bucket for a new source of water the result is exactly the same to the RWP.   It needs suction to pull from either the bucket or the lake.
Now if he used a new hose and connected it to the RWP and inserted the new hose into the bucket he could rule out all other leak paths on the intake side of the RWP.

I had a buddy lose an impeller at the lake when we had packed in for a 5 day trip.   His impeller chewed up and spit chunks into his hoses on the engine side.
We had a spare and tools so no big deal right? We dug out what we could. Thought we had all the old impeller chunks recovered. When he fired up again it kept running hot.   We ended up pulling the hoses off again and found a few more chunks of the bad impeller still blocking the water flow, the second time we removed the hoses completely off the boat so we could look down through them and found some wedged chunks.   At home we could have blasted water through them with a garden hose but at the lake we had to remove them to clean. It can happen even when you think you are being careful. After the more thorough cleaning his boat was good to go.

Jonny Quest wrote:    I would "shoot" temps at the heads, block, block circulating pump, risers, JQ

And directly next to the temp sender to see if it coordinates with the gauge.

SNobsessed wrote: Another thought - Maybe it isn't getting as hot as the gauge says? You could use an IR thermometer to check actual temp.

Suggested back on the 4th of Aug

Brian - We would love to know what you find out about the sensor.

When you change it, see if you can find an ID #.

Either someone put the wrong one in, or it changed resistance due to old age.

Information like this helps everyone on the site.

I had a similar thing with mine where ultimately a new gauge was the fix.

Overall low dash voltage problems, common with these 80s - early 90s boats can cause wacky gauge readings as well. If all of your gauges dip when you blow the horn or turn on the blower or bilge pump, that’s a clue.

gibson1525 wrote: Update I replaced the temp sender and no luck. It is still reading 180s when the thermostat housing is reading 140s.

8122pbrainard wrote: And directly next to the temp sender to see if it coordinates with the gauge.

You're not listening!!    The T stat housing is where water that's not needed is bypassed to the manifolds so, you may be reading where cool water mixed with hot.

gibson1525 wrote: Correct me if I'm wrong but the bottom of the thermostat housing and right next to the temp sender should read the same temp. I've been taking my temp readings from both those places every time and they are always very close. The top of the thermostat housing is always a fair amount cooler than the bottom.

Everything you wrote above is right.

As you mentioned it sounds like an electrical issue since all of your gauges are reading wrong   

Sorry for the confusion. Thanks for the help, I'm a novice when it comes to this stuff and I appreciate all the solid advice I get here.