Normal Operating Temp M35

[lucky]

 cmainprize
I have installed a water strainer on the hose from the pump output to hx.It is about 6 inchs from the pump.If the impeller comes apart the strainer will catch the pieces,also I have not noticed any water restrictions.
Al Landry
Lucky hull #13
1986 c 34

[Ken Juul]

Added some pictures of the HX to the Tech Wiki.  Engine Section, Cooling. 
Collected them from various posts on the forum.

[rmbrown]

Can anyone point me to the operating temperature range of a Universal M35A(C) in the manual?  I see the original post lists 165-195, which is in line with what I'm seeing, but I keep reading about folks getting 165-175 over the entire RPM range.  I'm seeing about 190 at 2300 rpm and 6.4 kts.

[Dave Spencer]

Hi Mike,
Page 5 of the M35A(C) manual states the normal operating temperature is 150 - 170. (Admiral panel notation). This seems low to me. I have a 165f thermostat and I regularly run at 165 almost regardless of the load or speed. I've verified this with a handheld temp "gun". I think the next common thermostat for our engines is 185f. I suspect this is what you have if you regularly see 190. I don't see this as a big deal. I consulted with my diesel mechanic friend and his comment is that 150 is too cool for a diesel to run. I think (and he thinks) 165 - 195 listed by the original poster is much more reasonable.  I would be concerned if you had a 165 thermostat and was running at 190. This would point to another issue with the system in my view.

[rmbrown]

I thank you!  I swear I looked all over but missed it every time.  That said, I have a working 160 degree thermostat in a full, burped system, with a clean strainer, a clean thru hull and a freshly boiled out heat exchanger.  I'm currently stymied.  It idled at 160 fine.  I left the marina and ran it up to 2500, near the top of the 2100-2600 cruising range but still in it.  The temp ran up to 185-190 (looking at the gauge, which I have compared to my IR temp gun).  I idled back down to 2300 and kept running (6.3 kts) and the temp eased up a little more.

On my first run with it, I ran it about 2500 for 20 minutes and set the 210 degree alarm bells ringing.  That day I hadn't yet burped it but it adds to my paranoia.

The hunt continues. :)

[KWKloeber]

Mike,

I've heard of a situation where the water injection tee became nearly fully blocked with scale and so the seawater cooling flow was way reduced.  Verify that you have full flow to the muffler.

kk

[rmbrown]

I definitely have flow at the muffler, and the flow looked good to my mechanic... but without measuring it, not sure how to confirm?

I'm gonna show my ignorance here and admit I don't know where the water injection T resides, though.  I just had the riser and hump hose replaced.  Would that have been open and visible at the same time?

[KWKloeber]

The cooling water is injected right above the hump hose, where the 5/8" hose  from your vented loop enters the riser.

[rmbrown]

Ah... so replaced as part of the riser?  In that case, it's brand new, so not likely the culprit.

[Craig Illman]

A couple more places to check, from my experiences, 1. see if there's salt build up where the raw water enters the heat exchanger, 2. check for any zinc fragments by removing the port end cap on the heat exchanger. It looked like I had good flow too, but a zinc fragment (or two) left from a PO shifted and obstructed the tubes enough to raise the temp at higher RPMs.

Wish I was in fresh water to run the engine up at 185.

Craig

[rmbrown]

Craig:

Due to time constraints, I paid someone rather than attempting it myself, but the heat exchanger was just removed, boiled out, repainted and replaced.  I didn't get to see it but the mechanic said it was full of scale and partially obstructed so we both assumed that was the culprit.  As it turns out, it was definitely overdue maintenance but not the root cause.

Re fresh water, my boat is less than a mile from the imaginary fresh/brackish line in the Tar/Pamlico river so I'm fairly fresh... but want to see that temp run way more steady and not vary with RPM, at least within the cruising RPM range. :)

[rmbrown]

Because it may help someone in the future... I've been using the boat for 3 years and could always work around the temp fine... 2100-2200 gave me nearly hull speed and I didn't need wide open throttle or to cruise at 2600, but if I tried, the engine would start heating up and as it started to pass 190 without slowing up, I'd slow down.  Since I got the boat, I've increased the size of the thru-hull, the strainer, the hose to the engine, replaced both the impeller and then the raw water pump, I've replaced all hoses so I'm comfortable none are blocked, I've taken apart the heat exchanger and cleaned it out, I've replace the exhaust elbow and riser, I've even replaced the coolant pump (because it failed, not for this reason)...

With any luck, I'm about to take the boat on a 4 month trip in 6 weeks so I brought in a pro.  He spent some time with me going over the engine but ultimately, he had me replaced the coolant cap (I'd pressure tested both the cap and the system) and he cleaned out the (embarrassingly nasty) air filter which was oily and full of insulation dust, and the engine never gets above 165 even at WOT.  Runs like a top.