Low Coolant Temperature

My son and I took the boat out for a steam-about yesterday. We were on the water for about 3 hours. Everything ran smoothly, with normal engine temperatures. On return I docked, and we spent 10 minutes or so "turning the boat" and playing with lines just before shut down. Just prior to shut down, I noticed the coolant temperature (gauge) was about 20 F below normal operating temperature. Additional information:

- Ford Lehman 135.
-about a 10 minute run up the harbour at 4.5 knots, which is about 1,000 rpm.
- water temperature is very cold right now--water temperature at Hope was 1.5-2.0 degrees C. I'd be surprised if the temperature at Steveston was more than 3-4 degrees or 37-39 degrees F. (Edit update: according to this, 3.9 C)
http://aquatic.pyr.ec.gc.ca/RealTimeBuoys/Default.aspx

Wondering if the thermostat is going wonky or is this "normal" given the cold water.

Most thermostats have a little bypass flow, don't know if that is enough to pull the temp down. Do you have a cabin heater or water heater tied to the coolant loop? Neither of those are blocked when the thermostat is closed.

Ted

Not unusual for a bit of leakage through thermostat. Sometimes this is intentional with a drilled hole or wiggle pin. It causes no problem, but when sea temp is super chilly, it will subcool the engine at dead idle.

As long as temps go to normal when you put a load on it, good to go.

O C Diver said:

...Do you have a cabin heater or water heater tied to the coolant loop? Neither of those are blocked when the thermostat is closed.

Ted

Click to expand...

Yes, I do, but it was not in use yesterday. The valve was in the mid line position but the pump was off, i.e. "Engine Heat" for the hydronic heat was off. FYI my young grandson was with us yesterday, and it was a bit of a challenge to keep him "inline" while I was doing things at the end of the day, so I didn't explore this more fully.

Jim

Since the cooling showed only when idled and the seawater is cold don,t worry.

Unloaded diesels produce little heat at idle and wee bit of coolant bypassing the t.s. may do this.
Next run just watch it and be sure it comes up properly under load.

My different engine did the same if idled in winter.

Thanks people. I figured as much but I thought I'd throw this out there for opinions.

I'd change the thermostat,

Check the new one before extraction and the old after.
Pretty easy job and inexpensive.

My Mitsu runs 180 - 190 (usually closser to 190) all the time and dos'nt take long to warm up. About 5min at idle. I have an old Nissan car (87) that warms up fast .. love it. My 13 Jetta w 32kmi takes much longer to heat up and I only have the heater output as a temp gauge .. don't like. The Nissan was even worse than the Jetta before I put a new thermostat in it.

If an old thermostat that is'nt bringing about a fast warm up or not keeping the temp up I think it should be replaced.
An engine running nice and warm will help keep the oil temp up and for FL's that's a plus.

I think that it is completely normal for a diesel to cool off when idling. The Perkins in our boat will drop 20 degrees when I'm not running at a cruising rpm, and the modern diesel in my pickup truck will cool from it's normal 200F to about 180-185 if it idles for a few minutes.

Eric- The mitsi and nissan are indirect injected, so lots more heat goes into the coolant at idle. The VW and Ford/Lehman are direct injected and put way less heat into the coolant at idle.

Replacing the tstat due to idle subcooling in cold water is likely a fool's errand. The tstats are often designed with a small bypass flow so sensor bulb gets exposed to actual coolant temp.

Also, the ford has sea water cooled oil, so coolant temp has little effect on oil temp.

I also have a FL SP135. For the first 5 years of ownership operating temp was at 160. Since it was always at 160 I thought that was normal, not to mention that running cool seemed like an advantage. It was common for us to trail a plume of white smoke and sometimes leave a fuel sheen on the water following shutdown. Eventually I investigated and learned that almost all (if not all) 135s were shipped from the factory with 160 degree thermostats. Once I switched it out with a 180 degree (as is recommended) the steam and the sheen went away (not 100%). Engine is now operating at correct operating temp and is happy. I dont recall the engine temp dropping when at idle. Worthwile to replace and be sure the thermostat is a 180, IMHO.

Ski in NC said:

Eric- The mitsi and nissan are indirect injected, so lots more heat goes into the coolant at idle. The VW and Ford/Lehman are direct injected and put way less heat into the coolant at idle.

Replacing the tstat due to idle subcooling in cold water is likely a fool's errand. The tstats are often designed with a small bypass flow so sensor bulb gets exposed to actual coolant temp.

Also, the ford has sea water cooled oil, so coolant temp has little effect on oil temp.

Click to expand...

OK Ski,
I was always amazed how my engine warms up so fast. Nice to know it was just something I just did'nt understand.

C lectric said:

Since the cooling showed only when idled and the seawater is cold don,t worry.

Unloaded diesels produce little heat at idle and wee bit of coolant bypassing the t.s. may do this.
Next run just watch it and be sure it comes up properly under load.

My different engine did the same if idled in winter.

Click to expand...

At idle, in 78 degree water, our FL SP135 wont come up to temperature but does quickly under load.

Our normal running temperature is 180 F and once it's to temperature, it stays there. I just noticed the lower temperature yesterday and as mentioned the river temperature is 4 C. Southern Georgia Strait temperature at Halibut bank is 7 C.

We get a little blue smoke on startup. We get a little "steam" when it's cool but high humidity (fall period). No white smoke or "Seam yesterday although it was near freezing outside.