Thermostat Operating Temperature

GrowingLad

GrowingLad

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Hi Guys,

I'm going to check in the manual later but I don't recall seeing anything.

I'm trying to track down a new thermostat for my VP AQ115. I've been told that the thermostat is off a very old style and not possible to find the same model...but, they do have a thermostat that looks slightly different but will fit and do the job. Now the chap asked me what operating temperature is the thermostat. I will check when I get in to see if I can find something stamped on the thermostat but I thought I'd ask here now, just in case someone already knows the answer. The part is coming from a car spares supplier but I take it a thermostat on a boat engine is the same as that of a car?

I'm not sure if it makes any difference but the boat will be used in the Med where the sea water is on the majority quite a bit warmer than the UK.

Many thanks,
Simon.
 
[ QUOTE ]
but I take it a thermostat on a boat engine is the same as that of a car?


[/ QUOTE ]

We were advised that the opening temperature for the thermostat on our Volvo MD6A motor was substantially less than that for the 'standard' automotive ones; I don't remember the exact figures, but something like 63C rather than 75C. As a result we paid about £40 for a Volvo one, rather than £10 at the local auto factors; however, when that one died too (After only 3 seasons /forums/images/graemlins/mad.gif) we followed the advice of several acquaintances and just ripped the centre out of it and 'free-flowed' the cooling water - we too are in the Med and have noticed no difference in engine performance as a result.
 
The opening temperature on a raw water cooled engine such as the MD6A will be aroung 65deg, whereas on a freshwater cooled engine it will be similar to automotive products. i.e. much higher.

Don't know what type the OP's engine is, but this should be a guide?
 
Many raw water cooled engines are actually set to max 60C to prevent scaling developing in the water tracts of the engine. This is well below optimum operating temp - but better than having to clear blocked water tracts.
Heat exchanger or fresh-water cooled engines generally of boat diesel type as the Perkins state temps from 65 to 93C, as they are not so susceptible to salt deposits in the tracts.

So it all depends on type of cooling system - raw or heat exchanger.
 
I dont know about the engines discussed,but I do know that on some engines if you remove the thermostat you can lose water thro, the filler cap as there is nothing to slow the water coming from the water pump.and it opens the spring loaded cap and vents it out.
 
Look at the Owners Manual!

It is in the "Technical data" at the back of the book.

Starts to open at 54C much lower than the one for the car, surprisingly low in fact!

They are usually marked but it might be marked in °F or in °C. If there are two figures the higher one is the temp at which it is fully open.


The thermostat fitted in the B20 car engines had an additional flap that closed off a recirculating,or bypass,connection to the pump inlet when it opened. However as far as i can see the 'stat in the AQ115 is of a conventional design but with a much lower opening temperature
 
Hi Guys,
Thanks for the many replies.
Okay, back home now and I've checked both my manuals, the American one states that for all petrol engines the stat starts to open at 82* C and fully open at 92*C.
The official VP manual states (as VicS) mentioned is 51*C fully open at 56*C

When I cleaned up the old thermostat it's got 55*C stamped into it....

Lets see if my man can get one so low....I bleeding hate all of this 4x as expensive just coz it's marine.....watcha ya gonna do /forums/images/graemlins/frown.gif
 
Hello again chaps,

I was giving this some thought after speaking with the car spares guy yesterday.

The lowest temperature I can get is 70*c (at least without going to marine).

I can understand that from new the engines were designed for maximum life, and hence with a raw water cooled engine the stat was very low as someone mentioned about the scaling.

Considering that the engine doesn't have so many years left in front of it, plus the boat lives on a trailer so will be getting flushed with fresh water after every use, am I likely to face any major problems with using a high temperature rated thermostat.

I can understand going by the book on a new engine to keep things running for many years with low maintenance...but in this instance the extra cost of a marine stat seems a little excessive for something that's in it's twilight years....

Or am I about to do something very silly?
 
In the early days many engines didn't use stats - they relied on variation of the cooling intake valve. Perkins ... OK I know it's a diesel, but they had Owners Manuals describing how to control engine temp with partial closed intake.

My wonder is whether it would really be bad if you didn't have a stat in ?

But surely it must be possible to get a stat suitable from a 'dare I say it' marine based outlet ?
 
I'm waiting for a quote on the marine variety....I'm not holding my breath it's going to be around the 6 quid mark as the car one.

Stat or no stat, eventually the engine will run at around 85-90*c once it's warmed up, am I correct?

So why would the stat opening at 50 or 70*c make any difference?

Or, would the stat opening at 55 mean that the engine would actually be running at around 55*....Sorry for my silly questions but as always, it's all new to me.

Thanks as always,

Simon.
 
[ QUOTE ]
Stat or no stat, eventually the engine will run at around 85-90*c once it's warmed up, am I correct?


[/ QUOTE ] No with no thermostat the engine will obviously warm up to some extent but it is the thermostat that controls the operating temperature in the ranges we are looking at.
Car engines are run at a fairly high temperature for a variety of reasons and indirectly cooled marine engines can run at similar temperatures.

Engines cooled with sea water must be operated at a much lower temperature to avoid excessive scaling and corrosion rates that would result from running on a once through seawater system at higher temperatures.

It is inadvisable to operate an engine below the design temperature for several reasons including efficiency and health of the lubricating oil. If the engine remains cold there will be a build up of condensed water in the oil and there may be a tendency for water to condense in the cooler parts of the engine.

I must confess that it has only just dawned on me that the AQ115 is directly seawater cooled. I'd assumed that because it was a marinised car engine that it would be indirectly cooled. That's why the thermostat has such a low opening temperature! For the reasons above it would be a serious mistake to use a car thermostat which would open at 75 or even 80C.
 
is the old one completely defunked? if not you could drop it in a pan of water with a thermometer and heat it uptill you see it operate, and note the temperature.
 
I'd sort of assumed that it was buggered as the engine was starting to overheat and when I took the stat out it was looking very worse for wear and not moving very freely.

At the beginning of this I just though, buy a new one, few quid, something else replaced that was probably well past it's sell by date.

I'll wait for the wife to pop out and give it a whirl in a saucepan. /forums/images/graemlins/smile.gif
 
I shall give it a whirl...
A few days ago I just though a thermostat was nothing special and they were all the same...okay, they aren't micro computers but I know a bit more about em now than I did before. cheers chaps!!
 
[ QUOTE ]
I shall give it a whirl...
A few days ago I just though a thermostat was nothing special

[/ QUOTE ]

Wait till you get the quote for a low temperature thermostat an then you will realise how special they are, oh an make sure your sitting down /forums/images/graemlins/grin.gif
 
[ QUOTE ]
make sure your sitting down

[/ QUOTE ] Sit down then. <span style="color:white"> ........................................ </span> £26.58 excl VAT from Keyparts.
 
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