How hot?

[Dave_Knowles]

Can anyone give me an idea of what my water tekperature should be when the engine is hot?

Dave


<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[Stemar]

Your engine wants to run close to 100 deg C for greatest efficiency, but that may not be possible.

With raw water, anything above about 60 deg C will cause deposits in the waterways, a bit like a kettle furring up, so it should be around 55-60 deg

If you have fresh water cooling, your fresh water wants to be between about 95 and 100 deg C, or even a degree or two higher. It's prevented from boiling by the pressure in the system.

<hr width=100% size=1>

 

[oldharry]

Most engine thermostats are set to open at either 82 or 88 degrees C. (There are exceptions of course) , so the off load coolant temprature will not go much higher than that. On load figures will depend on the efficiency of heat transfer in the heat exchanger., but I would be concerned if the coolant temprature normally runs more than 10 degrees above the thermostat rating.

Raw water cooling should not exceed 55 - 60c because of salt deposition problems within the engine. This is of course far too cool for efficient engine operation, so direct cooling is always a compromise except in engines specifically designed for it, as most (but by no means all!) outboards are.

<hr width=100% size=1>

 

[Dave_Knowles]

I am a little confused. The temperature that my engine is running at is just under the red sector of my gauge which goes from 100 to 240F. I see that my thermostat does nor fully open until the temp is 198F. Could it be that I have the wrong Volvo gauge fitted? Everything in both the sea water and fresh water system has been fully serviced and cleaned out. The manifold is staying cool and you can take the radiator cap off when the gauge is reading just under the red without any signs of boiling. The thermostat housing does feel very hot but I suppose 198F is very hot.

Dave

<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[oldharry]

Re: How hot? SAFETY WARNING

At atmospheric pressure water boils at 212F, so 198 is quite hot enough to take your skin off! The higher temprature is acheived by pressurising the cooling system, which allows the engine to run hotter and more efficiently, without boiling the coolant.

I have never checked a Volvo gauge, but usually the red sector comes in at around 220F, at which point the coolant will start overpressurising the system and blowing off through the radiator cap.

As long as it is not blowing off, or losing coolant, and the gauge is not actually reaching the red sector, then it is operating within what the manufacturers would regard as the 'Normal' range for that specific engine (I said there are exceptions). The actual reading of the gauge is not important, and it is there to tell you if something starts to change like cooling down or getting hotter than usual, so that you can shut down before damage occurs.

IMPORTANT SAFETY WARNING:

You should NEVER remove the radiator cap from any engine at operating temperature. If it had pressurised (which it will on a run) you would now be in hospital with severe burns. You MUST leave it at least 20 minutes after shut down before removing it, and even then cover it with a thick cloth before releasing it. That way if it is still pressurised the water is deflected away from your face.

I saw it happen once - the bloke undid the rad cap,and received a jet of boiling water straight in his face. He will carry the scars to his grave, and nearly lost the sight of one eye.




<hr width=100% size=1>

 

[Gunfleet]

Re: How hot? SAFETY WARNING

Agreed. I knew a girl who took the cap off an MGB rad while it was hot and was visiting the hospital for several years after.

<hr width=100% size=1>

 

[Dave_Knowles]

Re: How hot? SAFETY WARNING

I think from everything that has been said that I probably have a problem with the gauge. It always has been just on the line between green and red. The Volvo gauge is the old type with no reference other than green and red. I always thought that gauges should indicate about the middle when everything was running normally.

By the way I didn't take the cap off it was a marine engineer that did while he was checking my engine which he had rebuilt. But then once at ITN where I worked as an editor an electrician who did not want me to bother unplugging a machine he was to check ended up being thrown across the room by the electric shock he got when he found the fault.

Dave

<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[oldharry]

Try replacing the sender. The meters usually either do or dont work, but the senders can get very inaccurate.


<hr width=100% size=1>

 

[Dave_Knowles]

The sender is brand new and is reading about the same as the old one. I have had the header tank cleaned out and checked, new thermostat,the manifold is almost new, new oil cooler, all the pipes have been off and checked so what else can I do? The consoling thing is the manifold is cool so therefore I am getting a good sea water flow.

Dave

<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[oldharry]

Unless the meter itself is faulty (can you borrow one to see if it makes any difference?) then its not easy to advise much further without actually being able to see what is going on.

I suggest that you contact Volvo and ask them if that reading is normal. Otherwise you need to find some way of actually measuring the coolant temp in degrees F or C to see if Volvo think that it is within limits. If you have a thermometer which reads high enough (eg a glass oven thermometer will do), remove the rad cap at cold and run the engine up without racing it. You may loose some coolant and make a mess doing this. And as I said earlier the coolant will be near boiling point when it has warmed up. Switch the engine off before taking the reading to avoid any risk of splashing and wear a pair of heavy duty red kitchen gloves.

Check coolant levels when it has all cooled down again after doing this, and before using the boat again.


<hr width=100% size=1>

 

[Trevor_swfyc]

Re: How hot? SAFETY WARNING

Not sure I understand what the problem is, if the gauge has always read the same then then the temperature is no higher or lower than normal. The gauge is a guide that things are normal and it sounds as though they are. If the thermostat did not open then you would see the gauge go above its NORMAL position, equally if the salt water intake became partly blocked.

I have a SONPAR minature precision thermometer range -40 C to 100C accuracy claimed + - 1 C, display is digital to 1 decimal place. They are available from aquatic stores this could be fitted into a probe socket in the head, to give you an accurate temperature of the water in the head which it appears you are interested in. The good news is the thermometer only cost £10.

On the safety point even if the water is below 100 C an air pocket in the system could still cause the water to blow all over you when the pressure is released. I think we all have stories of idiots who think it clever to work unsafe, fortunatly it is now against the law.

Trevor

<hr width=100% size=1>

 

[Dave_Knowles]

Re: How hot? SAFETY WARNING

Hi Trevor,

The only problem I have always had is that it seems (by gauge) to be running very hot and I am not sure when it is over heating. On all cars I have had the gauge will start rising to wards the red if there is a problem. On my boat I am already on the red so I was just trying to work out with the forums help as to what the average temperature normally is in other boats. Surely not all Volvo engine are on the red when running normally.

Anyway all the replies so far have been useful and gives me food for thought.

Dave

<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[Trevor_swfyc]

Re: How hot? SAFETY WARNING

Dave,

My Volvo 2002 hasn't got a temperature gauge, all it has is an alarm which went off when I lost the cooling water out of the heat exchanger once. Do you have an alarm as well as a guage, if so and the alarm never goes off then you have no worries. Unless the gauge is calibrated it means nothing, you could calibrate it yourself. Put the sensor into water and heat it slowly with a 0 - 100C thermometer recording the temperature. From a point when the guage starts to read take a digital picture of the guage every 5 degrees centigrade you will then be able to convert the reading you see on the guage when in use to an approx temperature. As somebody else pointed out this will be controlled by the thermostat which can also be removed and checked for its opening temperature range in a similar way. I would expect the temperature of the engine coolant under normal running conditions not to exceed the temperature at which the thermostat is fully open.

Trevor




<hr width=100% size=1>

 

[SteveA]

Re: How hot? SAFETY WARNING

I had similiar concerns about the temperature guage not reading correctly so got a non contact infra red hand held thermometer and was able to check the guage against this. i found that the guage was reading about 30 degC high- I don't know if this is a fault on the gauge or (new) sendor. It's also useful for checking the stern gland temp if like me you find it diffecult to reach.
These thermometers are readily available on ebay for about £25.00
Steve.

<hr width=100% size=1>

 

[Dave_Knowles]

Re: How hot? SAFETY WARNING

That sounds a good idea to ease my mind because I cannot see the point of a gauge that reads silly temperatures. I might as well take it out if is giving me false readings.

<hr width=100% size=1>http://stores.ebay.co.uk/mycleopatrachandlery

 

[oldharry]

Re: How hot? SAFETY WARNING

<might as well take it out if is giving me false readings. >

....Yes but then you have no overheat warning device if the intake pipe blocks! If something goes wrong the gauge will tell you by changing from its usual reading, and before expensive damage takes place! But you do need to know what is 'normal' for that gauge,

<hr width=100% size=1>