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Engine Temperature lower than usual


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Hello all,

I don't think the coolant in my engine has been changed in a long time and it is one of the jobs I suspect after this is going to happen sooner now. I had noticed my coolant was just a little bit below level so topped up with about Two pints of fluid...the engine not me! My friend had previously suggested that "Coolant doesn't really lose it's anti-freeze properties but does lose it's corrosion properties, pop a bit of Fernox in" so this is what I did adding 500ml of Fernox F1 along with a 50/50 antifreeze mix up to the correct level. After a winter lay-up with only a few trips to the local water point I noticed the engine wasn't getting up to the usual temperature which I had put down to the relatively short trips...

I have recently however been on a couple of runs that would normally get the engine up to temp.

I have a Perkins M92 with keel cooling which has consistently run at an "indicated" 77 Celsius but now seems to run cooler at 65 C. These figures would be the same whether chugging along with the stream or pushing hard against it, summer or winter. Perkins recommends a 75 C stat for marine applications 82 for automotive and industrial.

My first thoughts are what has changed, which is nothing bar the addition of the Fernox.

Is the Thermostat at fault, if nothing had changed and the engine failed to warm up this would be my first port of call.

Is the gauge working - yes - or innacurate - probably - I haven't got a thermometer that can say for sure but will get one for testing.

The hot water to the calorifier and hoses feels hot although having a shower this morning the hot water did seem to run out sooner.

The engine hose from the stat to the keel cooler is hot to the point I can't hold the metal fitting for more than a second or two and the return to the engine is cooler, I can comfortably hold that so coolant is flowing around the circuit.

The engine seems to run fine, no smoke, no unusual noises.

So questions:

Could the addition of the Fernox have somehow made the coolant more efficient? Like those additives for cars with boiling issues due to modifications?

Could the stat have gone faulty just at the time of the top up and should I take it off and see if it operates properly in the saucepan test? Or replace it anyway?

Is a indicated temp of 65 C too low and will it cause a problem? So am I worrying unduly...

 

And perhaps before all that I suppose I had better change my coolant...

Any thoughts welcome.

Edited by Paringa
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When my boat did similar things I replaced the thermostat and everything worked fine.

The advice I got - and I think from your comments you know this - was that the temperature reading on the gauge was not very accurate in absolute terms, so you need to know what is "normal" for your boat at various engine revs and then take action when something "abnormal" happens.

I bought a cheapo digital thermometer with a  probe - the sort of thing you see people stick into food in restaurants.

Edited by Scholar Gypsy
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4 hours ago, Paringa said:

Hello all,

I don't think the coolant in my engine has been changed in a long time and it is one of the jobs I suspect after this is going to happen sooner now. I had noticed my coolant was just a little bit below level so topped up with about Two pints of fluid...the engine not me! My friend had previously suggested that "Coolant doesn't really lose it's anti-freeze properties but does lose it's corrosion properties, pop a bit of Fernox in" so this is what I did adding 500ml of Fernox F1 along with a 50/50 antifreeze mix up to the correct level. After a winter lay-up with only a few trips to the local water point I noticed the engine wasn't getting up to the usual temperature which I had put down to the relatively short trips...

I have recently however been on a couple of runs that would normally get the engine up to temp.

I have a Perkins M92 with keel cooling which has consistently run at an "indicated" 77 Celsius but now seems to run cooler at 65 C. These figures would be the same whether chugging along with the stream or pushing hard against it, summer or winter. Perkins recommends a 75 C stat for marine applications 82 for automotive and industrial.

My first thoughts are what has changed, which is nothing bar the addition of the Fernox.

Is the Thermostat at fault, if nothing had changed and the engine failed to warm up this would be my first port of call.

Is the gauge working - yes - or innacurate - probably - I haven't got a thermometer that can say for sure but will get one for testing.

The hot water to the calorifier and hoses feels hot although having a shower this morning the hot water did seem to run out sooner.

The engine hose from the stat to the keel cooler is hot to the point I can't hold the metal fitting for more than a second or two and the return to the engine is cooler, I can comfortably hold that so coolant is flowing around the circuit.

The engine seems to run fine, no smoke, no unusual noises.

So questions:

Could the addition of the Fernox have somehow made the coolant more efficient? Like those additives for cars with boiling issues due to modifications?

Could the stat have gone faulty just at the time of the top up and should I take it off and see if it operates properly in the saucepan test? Or replace it anyway?

Is a indicated temp of 65 C too low and will it cause a problem? So am I worrying unduly...

 

And perhaps before all that I suppose I had better change my coolant...

Any thoughts welcome.

The engine temperature is controlled by the thermostat, so if the coolant were 'more efficient' at carrying away the heat the thermostat would not open as much to keep the correct temp.  If you have an engine temp of 65c and a thermostat of 75c then there should be little if any hot water passing to the skin tank as the coolant is not hot enough to open the thermostat.  So at a guess it is either all ok and the gauge has gone wrong, or the thermostat is opening too soon, or never closing fully.

  • Greenie 1
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  • 2 weeks later...

On my engine the temperature gauge sender is screwed into the dome thing on top of the stat housing. When you drain and refill the water it is inevitable that there is air in the dome and the temp reading can be awry, loosen the sender and bleed the air out. Saves buying a new thermostat every time you fiddle with the water system!

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