No water going to HX

[Porchhound]

While anchored I took the spare time and cleaned more on the intake system of the HX. I thought I had done a good job but more scale came out, and the engine ran cooler (170F vs 185-190). I'm letting lime away soak in there now via the inlet hose. I hope it doesn't eat my hose! The 2inch HX only has one end that opens, making cleaning more difficult. I guess a radiator shop will be the best bet.

I disconnected the ground on the heat sensor (it's just the bare end of a wire) and repositioned it for more contact. The gauge began working again, but it still reads about ten deg higher than the FLIR. Of course the sensor is having direct contact with the coolant. I'm going to borrow from your photo KW and add an end to that ground cable the clamp can grab.

As always, thanks for all the help!

[KWKloeber]

ABA #17 stainless Mini Clamp.

So?  Haven't answered why it's a good idea to bond the Tstst separately?
(and why just bonding it back to a nut on the water flange is not the best way)

As the troubleshooting guide says, Temp readings are +/- 15%

[Porchhound]

From what I'm reading, bonding directly results in an accurate ambient Ohm reading to the sensor, thus accurate readings as the temps go up. I'm still reading about this system. I never really knew how resistance temp detectors worked.

[KWKloeber]

You have a Tstat cap that sits on top of a Tstat and gasket, therefore doesn't directly contact the Water Flange underneath.
The water flange has a gasket so doesn't contact the engine block.
The bolts that hold both those are subject to corrosion.  Looking at the pic of your cap it's obvious that the bolts aren't making a good, clean bond and who knows what corrosion is on the threads.  My Tstat cap bolts were so corroded in that I had to drill them out and buy a new cap.

The proper place to bond the Tstat cap is to a known good ground, not to a water flange bolt head. It's probably irrelevant because my guess is that your engine block and panel probably are not properly grounded (unless PO did the mods needed to do that.)  So the bandaid bond of the TStat and messing with the temp gauge wiring is just that, bandaids until you "get into" bringing the 'lectrical up to snuff.  12v stuff like the panel will work but with the temp gauge (and fuel level) the senders AND gauges all need to be grounded properly to read accurately.
It never ends on a boat!!  If/when you want to tackle a 'lectrical upgrade we can walk you thru that.

[Stu Jackson]

While anchored I took the spare time and cleaned more on the intake system of the HX. I thought I had done a good job but more scale came out, and the engine ran cooler (170F vs 185-190). I'm letting lime away soak in there now via the inlet hose. I hope it doesn't eat my hose! The 2inch HX only has one end that opens, making cleaning more difficult. I guess a radiator shop will be the best bet.

.....................
......................
.......................

I had a 2" HX on my M25 when I bought my boat in 1998.  The PO told us the engine overheated if pushed to WOT for extended periods.  He said "it was normal."  He also gave me ALL of the back issues of Mainsheet magazine back to 1987 when tech articles began to appear that included the C34 (although the M25 engine appeared in C30s and C36s back then, too).  So I read all those back issues, and as some of the sticky topics explain, on Xmas Day 1998 I started the Tech Notes Index and the Association built the Tech Notes Online from that.  Included in that effort was a lot of information about those old smaller HXs.  I finally took mine off the engine completely.  And when I shook it it sounded like a mariachi band!:D  Lots of pieces of zinc fell out when I removed the single end cap.  But the REAL CULPRIT for the overheating was the buildup of salt on the inlet port.  This is where the salt deposits itself from the cold rw from the rw pump when it hits the hot HX.  Once I cleared that blockage out (more than half of the port was blocked) the engine ran cool even at WOT.  Years later I got the boat bucks together for a 3" HX.  You really need to remove it from the engine to clean it.  I don't believe a radiator shop is necessary.  Lots of folks talk about the tubes needing to be cleaned, but as a mechanical engineer, I note that the tubes is where the water moves the fastest and the tubes should be just fine.  It's the floating pieces of zinc, impeller pieces and salt in the inlet port that are the real issues.

The point is that what the tech notes since 1987 say is true: the 2" HX is marginal but OK for that engine if it is free and clean.  The M25XP engine is two more HP and it includes a 3" HX and the corrected alternator bracket.  I did both to my M25.

I sure hope you've done the alternator bracket.

[Porchhound]

I looked at the panel connections and it looks like an upgrade is in order. Somehow in the process of screwing around I removed the connector to my oil sending unit. It seemed loose so I crimped the female end of the bayonet connector and reattached, but in the process lost my alarm. I'm going to look for a fuse in that line.

According to the PO (who did several of the upgrades suggested on here) he replaced the "new wiring harness for the engine." The temp sensor gauge is new, as is the amp meter. There's obviously more to do in several areas, but that's okay. That's the only way to really learn a boat and its systems. Thanks for the offer. I'll take you up on that.

[Porchhound]

Stu, the alternator bracket upgrade was one of the first things I looked for during my initial walk-thru, thanks to all the tech notes and the list of "must-do's." The PO made that upgrade as soon as he purchased the boat several years ago. When we are back in the marina I plan on removing the HX and giving it a good cleaning, probably do a better job with the lime away with it off.

[Ron Hill]

Porch : If you still have an ammeter the PO did NOT do the wiring harness upgrade!!!  The main part of the wiring harness upgrade was to REPLACE the ammeter with a Voltmeter and take the alternator output and run it to the starter solenoid stud!!  There also was a wiring block that all of the wires connected into and the trailer connectors were cut out!!  Best you check your M25 wiring!!

A few thoughts

[Porchhound]

I misspoke, Ron. It is a voltmeter...kinda dates me I guess, but I will check the wiring.