SailNet Community

SailNet Community (
-   Newport (
-   -   Diesel operating temperature (

Drewboy 08-13-2007 12:17 AM

Diesel operating temperature
I have a 1983 Newport 28 with a Universal 5411 (raw water cooled). It seems like the engine never gets higher than about 120 deg based on the temp gauge and an infrared thermometer - but the specs say I should be running from 135 to 150. I've replaced the thermostat, the sender, confirmed that the gauge works correctly and know that all of the hoses and water flow are good. When I start the engine I get water out of the exhaust immediately.

Am I OK here? It seems to me that that I wouldn't see much water out of the exhaust until the thermostat opens up at 140 deg. I'm wondering why the water out of the exhaust isn't limited until the temp gauge gets above 140 deg and then the thermostat opens to let water out of the exhaust and bring new raw water in through the hull inlet.

Anyone with comments or thought are very much appreciated!


sailaway21 08-13-2007 01:50 AM

First off, the thermostat has nothing to do with the exhaust water.
Secondly, if you're running too cool your thermostat is opening too soon.

CapnHand 08-13-2007 07:48 AM


Originally Posted by sailaway21 (Post 179074)
First off, the thermostat has nothing to do with the exhaust water.

It shouldn't but it may. Usually there is a bypass so that water is always flowing through the exhaust but only cools the engine when it becomes hot. This may have been changed by a previous owner.

Drewboy 08-13-2007 11:10 AM

It is my understanding that the only way to get water into the exhaust is from the exhaust manifold and through the thermostat after it has opened at it's designed temperature (140 degrees). Before that happens the water in the engine gets recirculated through the engine as it heats up.

I'm trying to think of a way to prove that the thermostat is closed and water is recirculating during warm-up. Any ideas there?


hellosailor 08-13-2007 12:24 PM

Boat engine cooling systems are different from cars, usually there is a rubber (not metal) impeller pump and the coolant (your raw water) is forced to be in constant flow. The impeller blades would probably break off from the backpressure if the coolant couldn't flow. The system is set up so that there is always a flow from the pump--the only question is, where will that flow be directed. The thermostat is a diverter valve (a "Y" valve) rather than the simple open-close type in a car.

"First off, the thermostat has nothing to do with the exhaust water."
Sometimes it does. You'll get a trickle from the bypass circuit while the engine is cold, and then when the thermostat opens (often a "Y" valve on a raw water entire) the primary cooling lines allow more water to go through. Could just mean that the bypass lines are smaller, or more constricted.

Either way...
In raw water systems 140F is normal, because around that point salts crystallize out of salt water and jam the cooling passages. A very bad thing. If you are operating a diesel in FRESH raw water, inland with no chance of running in salty water, you can usually put in a fresh water thermostat which can bring it up to 170F-190F, a normal range for closed heat exchanger systems and fresh water. And, a more powerful and economical operating range for engines in general. (Obviously, to the limits suggested by your engine maker.)
But in raw salt water, you can't run an engine that hot. The lines will plug up totally in short order.

Drewboy 08-19-2007 04:43 PM

Update on 5411 running cool
I had the boat out yesterday to test the temperature control after replacing the thermostat and insuring that all of the lines were clear. After running 30 minutes at 80% engine RPM I found the temperature at the sender (near the thermostat) to be 110 deg - not hot enough to open up the thermostat (which is rated at 140 deg). I had some coughing water out of the exhaust from the start and throughout the run.

I find this very curious because I know the purpose of the thermostat system is to get then engine temp up to 135 to 150 and keep it there.

Any other ideas how I continue to track the problem down?

hellosailor 08-19-2007 06:58 PM

So your engine is running TOO COLD. Or, your sender/thermostat is wrong.

How did you check the temperature at the sender?

It would be most unusual for any engine to be operating that long under that load, and still not exceed 110F.

Drewboy 08-21-2007 01:02 PM

More on the 5411 operating temperature
For Hellosailer and others - I agree that the engine is running too cold. The thermostat and sender are both new and tested. The temp gauge is also good and I'm able to check temp with an infrared thermometer.

Based on a thought read elsewhere I made a run yesterday with the raw water intake seacock partially closed and guess what? The temperature went up and I could get it to the recommended range. I believe this worked because the thermostat bypass amount is too great and that lets colder raw water in from the start, never letting the engine heat up. Partially closing the seacock limits the bypass amount.

Any way to adjust the amount of bypass in the thermostat?

hellosailor 08-21-2007 04:54 PM

Well, yeah.
Preferably by checking that you've got the right part # for the thermostat and housing, first.

We needed a thermostat once and were told it would take a week to get one in. Didn't have a week. I picked up a nice stable golf-all-sized rock from the parking lot, put in in the housing, closed it up, and told the skipper "Don't Look".

It ran just fine that way. All you need is the right size rock (or baffle plate, etc. that can't get ingested into the engine.)

CapnHand 08-21-2007 10:02 PM

Do you have a copy of the engine manual showing how the engine cooling system should operate?

I'm not sure if the thermostat could be installed backwards and if so, would that make the engine run too cool or very hot?

All times are GMT -4. The time now is 08:23 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
(c) LLC 2000-2012

For the best viewing experience please update your browser to Google Chrome