Coolant system revamp

[theonecalledtom]

I was wondering if you peeps could help me with my next engine room project. Above 2300prm or so our water temp warning kicks in, refusing to then switch off until we restart the motor. This happens pretty much instantaneously and the temperature gauge shows reasonable temperatures (often lower than it would show after a period of running).

So part one of my plan is to replace the sender.
Q1: How to make sure I get the right replacement. Do I have to worry about the threading as well as the connection diameter?
Q2: Will I be able to replace the sender without draining (or leaking) coolant? I'm guessing not.

While doing this (partly assuming that I'm going to have to reprime the coolant) I figure that I might as well fix the crimp in the elbow created where the water heater plugs into the coolant system. It looks like I should be able to just add a metal L bend to replace the crimped rubber. This is displayed in the photo that will hopefully be attached.
Q3: Anything I should be aware of while making this change?

Assuming that I've now drained the coollant I'll need to reprime the system. The biggest issue seems to be knowing when I'm out of air pockets up at the hot water end.
Q4: How do I avoid air pockets at the hotwater end. How do I pump air out of the system without running the engine and risking ruining the impeller?

A friend suggested adding a valve up there to help bleed the system. This seems like common sense to me - is it?

I'll probably have more questions as I think about it more but what I would like is to make sure that tomorrow when at the boat I get all the right information (and some of the right parts perhaps).

[GordMay]

Sender type depends upon the gauge manufacturer.
North American Water temp. gauge senders are 29.6 (high) to 450 (low) Ohm.
European Water temp. gauge senders are 22 (high) to 281 (low) Ohm.

See also:
http://www.cruisersforum.com/gallery...=500&userid=79
http://www.cruisersforum.com/gallery...=500&userid=79
http://www.cruisersforum.com/gallery...=500&userid=79
http://www.cruisersforum.com/forums/...sting-645.html

[Maine Sail]

Before you go pulling and replacing parts I would suggest getting an infrared thermometer!

Also read the link bellow so that next time you'll have a baseline assessment of what your engine looks like when she is running correctly to compare against.

Engine Temp Monitoring & Over Heating Baseline Assessment (LINK)

[MidLandOne]

The easiest, but normally most expensive, source for temperature senders is from a stockist of original parts for the engine. Saves quite a bit of driving/phoning around, mistakes, etc.

If your temp gauge seems to be indicating low (don't know whether to interpret your comment as meaning that) then that is a possible indication that sender is sick too and will later fail.

If you have 2 senders (as I understand it you do) then the alarm one is a switch, not a variable resistor as the gauge one is. Apart from following the cabling, you can determine which is which by measuring their resistance (the switch alarm one will be open circuit, ie infinite resistance, when cold assuming it has not failed to open circuit, as it seems yours has not) - that assuming the temperature gauge one is ok because if that fails it will likely fail to open circuit (if so the gauge one may be able to be identified as often has a longer probe into the water space than the alarm one)

Not familiar with your engine but many modern marine engines have the DC isolated from the block, etc so the sender will have two terminals instead of one (single terminal ones the return is via the block). Get the correct one.

Your coolant pump is almost certainly a centrifugal pump just like an automobile's one, not a flexible impellor pump, so if it runs dry for a short time while priming, clearing air etc it will not be harmed. But very unlikely it would run dry in any event.

For the engine itself, many have removable threaded plugs in the high points of the coolant system to bleed air - just take them out and replace them as you fill up with new coolant and the level reaches the plug.

For high points outside of the engine itself such as for calorifiers, etc which may airlock I'd just suggest you not worry about it unless you find that it is actually a problem.

[theonecalledtom]

Hey Acoustic - I meant to add that after reading other threads here I'm also going to get one of those sensors - thanks! Right now I'm working on the assumption that something needs replacing in the system and that the crimp in the heating extension elbow should be fixed.

What sort of variation should I expect between the sensor pointed next to the sender and the temp gauge output? Maybe 5%?

Thanks for the reading material Gord. Unfortuantly the back of my instrument panel is about as accessible as Sarah Palin so my sender testing happens at the engine side. Something else thats on my list of "things to do" is to cut it out and put a nice shiny fold out unit in in its place....

[Chief Engineer]

It looks like a Universal Diesel..there should be a petcock/fitting on top of the therostat housing.....do you have the engine piped to a hot water heater?

[theonecalledtom]

Hi Chief,

Its a Universal 5432 with water heater plumbed in at a slightly higher level. If you click on the image you'll get a larger view (the heater is the large stainless cube in the background) but the image compression makes the small labels I added fairly illegible.

MidlandOne, will print your thoughts out and take to boat. The gauge and warning senders are both single wire units (I can't remember which is which but if you short them its pretty easy to find out from the instrument panel - this time I'll write it down!).

Do the senders back into the coolant directly or into a dry dock in the engine casing? In other words can I take them out without worrying about draining the fluid?

[MidLandOne]

Originally Posted by theonecalledtom

Do the senders back into the coolant directly or into a dry dock in the engine casing? In other words can I take them out without worrying about draining the fluid?

Am not familiar with the particular engine but almost certainly they will go into the coolant. It is possible to have senders which go into pockets but doubt that will be case - also appears in the photo that yours have a sealing tape on them so they go into the fluid if so (some bed onto a crushable metal gasket or similar and so don't need tape).

So you do have to drain the coolant down. Often there is a way to see how much coolant one has to drain down, for example in my own engine it is possible to monitor the level in the heat exchanger, as that has a cap on it, until the level gets below that of the sensors (or thermostat, if I was to change that for example). The senders are normally mounted high on the engine as yours are so you don't have to drain much out - if you are lucky your engine may have a valved hosetail or similar coolant drain fitting low down somewhere on the block (if a hosetail it may be valved inside so that you just loosen it in the block and the internal valve opens).

[theonecalledtom]

Originally Posted by MidLandOne

also appears in the photo that yours have a sealing tape on them so they go into the fluid if so

Excellent spot - that hardly shows up in the photo! I should have thought of that myself...

[Chief Engineer]

I reviewed your image.......

I have a feeling that the unit is plumbed incorrectly.....

With the heater higher than the expansion tank, when you open the expansion tank on the engine the antifreeze should flow out.......

I have seen boats that the owners tried to install separate heating units...like a car heater in the pilot house this unit was much higher than the engine.....to keep the enginefrom over heating, the coolan had to be added at the highest point i.e. a hose had to be taken off of the heater and antifreeze added there.

I don't quite understand the "tee" fitting at the front.

[Chief Engineer]

I reviewed the picture again....you should have no water circulating thru the heater because with your arrangement, you are effectively bypassing it.

Get rid of the Tee in the front that goes to the heat exchanger...put the sender in there and put the return line directly to the heat exhanger.

Fill both hoses at the heater then connect.

[theonecalledtom]

Heres a close up of the water heater unit. My first thought on seeing this would be to agree with the Chief and say that it shouldn't work, however after some time under power the other day I was a bit surprised to get some pretty darn hot water out of the system (smelly but thats a different problem to be solved on another day). So somehow water is getting through the water heater.

Perhaps the crimp in the 90 bend is narrow enough to create enough pressure difference to drive water through the heater rather than through the by pass?

Reading here: One guys experience reducing water temperature it seems that people have had problems running inline water heaters on similar motors.

So, my next steps are to:
Verify that

1. the temperature gauge readings are accurate
2. Tally all the components that would be needed to:

3. Replace the temp warning sensor
4. Remove the crimped tubing
5. Make refilling and bleeding easier

[Chief Engineer]

I reviewed your close up picture, that tee and that short piece of hose should be taken out.

It appears to me that with the current setup you are not getting optimum circulation to the hot water heater....you are pressurizing it from both ends.

[MidLandOne]

I wondered the same and really wouldn't like to say.

But my thought was that if both the connection to the calorifier and the return from it are taken off close together as they are, then there will be little difference in pressure between them and a thermo-siphon through the calorifier coil will likely work as the calorifier is well above the engine height. But as I say, I would not like to be very positive in saying that.

All the thread tape looks new as if it has recently been installed or revamped in some way - if so, whether it works reliably under various engine temperatures or not might not be able to be based on long past experience.

[Whimsical]

Maybe a dumb idea, I have plenty of those, but why not a ball valve in the short piece of hose. This could be used to supply some differential pressue and ensure there is flow to the heater or opened for maximum bypass if required.

Mike