Maximum temperature for a BMC 1.8 engine

[Grassman]

I have a BMC 1.8 engine and when cruising on rivers or the rare prolonged spells at 4mph on a canal the temperature regularly gets up to 100 degrees C which I was told was the maximum you can safely run a BMC up to without damaging it.

 

It's never been an issue really and at that temperature the engine doesn't seem overly hot (no steam, smell etc). However there may be times on fast flowing rivers where I'd like to give it more power but I haven't wanted to risk the temperature going any higher.

 

Another boater I met recently says that with the correct pressure cap (4lbs according to Calcutt Marine) and a coolant split of 50/50 you can safely run a BMC 1.8 up to 105c before it starts boiling over.

 

He has a chart which gives the maximum temperatures that each strength of pressure cap allows the temperature to go up to and it says a 4lb one is 105c.

 

Any thoughts on this?

[MtB]

I'd say by running an engine without adequate cooling as you describe, you are inviting trouble.

 

There is no absolute cutoff temperature above which your engine will suffer 'damage', the further from optimum temperature it runs the faster it will wear out and the more peripheral faults are likely to crop up (poor combustion, blocking injectors etc.)

 

As the water in the cooling system reaches 100C it will begin to boil. The steam will cause the system pressure to rise if there is a spring loaded pressure cap, and the rise in pressure raises the boiling point too, so the boiling is self balancing up to the point where the pressure cap opens and limits the rising pressure. Then all your coolant will boil away and your engine will knacker itself in very short order, probably seizing. You are running it with no safety margin if the skin tank can't keep the engine cool on a river.

 

So the fact that your temp rises much above thermostat temp at all is a really bad sign in my opinion. You need a bigger skin tank, probably.

Edited May 23, 2016 by Mike the Boilerman

[Tony Brooks]

Yes - you can boil an engine without damaging it as long a sit is kept full of coolant but it will not be kept full of coolant so we would be looking at potential head problems not so long after it starts to boil.

 

I think that it is very ill advised to try to run above 100C, in fact I would want to keep it below 90. The pressure caps and seats are not the most robust things and if they leaked at 100C plus the engine would boil.

 

I think that Calcutt fit 60 odd degree thermostats to reduce the calorifier temperature so there is something wrong if running close to 100C. If this is a narrowboat I would suspect undersized skin tanks but first check the thermostat, someone may have fitted an 88C stats and the temperature is when they starts to open , not when fully open.

 

[RLWP]

Assuming the temperature gauge is telling the truth, of course

 

Richard

[Slim]

Assuming the temperature gauge is telling the truth, of course

 

Richard.

 

 

Yes, my 1.8 always sat on 195 F (it was made in the era of imperial measurements and again the engine deserves appropriate instruments) When I had cause to change the sender (sold as matching) it immediatly started indicating around 205-210 F. It happens I fitted a new sender last week so when I get the engine going it will be interesting to see what the indicated temp is.

 

 

Frank

[alan_fincher]

 

I think that Calcutt fit 60 odd degree thermostats to reduce the calorifier temperature so there is something wrong if running close to 100C.

 

Calcutt recommend and supply a 74 degree thermostat if you are using with a calorifier or 82 degree thermostat if not.

 

If these are working correctly, and the cooling tank adequate, then in my experience those are pretty accurately the maximum temperatures it should reach even if worked hard.

 

(Subject of course to manufacturing tolerances and, as Richard says, the gauge being accurate).

 

If it goes a lot higher than those temperatures, something isn't right. I'd not want to run one at anything close to an indicated 100 degrees.

 

You seem to say that it is not just when worked hard on rivers that it is going to 100 degrees, but even for more moderate use on canals. If so, and you do push hard on a river I think you WILL have issues.

 

Has it always been like this, or is it something that has worsened over time?

[Grassman]

Thanks all of you for your advice.

 

The temperature gauge and thermostat have recently been replaced together with the sender units. The temperature has been checked and it matches what the gauge is reading.

 

I've had the boat 3 years and it's now 20 years old. I didn't really notice the high temperatures until last June when I went on the Trent and Ouse rivers. Before that I'd just done canals and therefore worked the engine much less. Since then it seems to be worse but I can't be certain of this.

 

Here's what else has been done;

 

Checked water pump is working okay.

Had gearbox checked and reconditioned.

Fitted a header tank 1 metre above the engine (inside the cabin).

Measured skin tank and confirmed it's large enough. I can't remember the size (7ft x 20 inches???) but it satisfied the equation for the hp.

Cut large section out of skin tank out which revealed 4 baffles which were vertical (unusual???) with a half inch gap top and bottom of each one. More sludge found to be lying in the bottom of the tank. The vertical baffles were removed and replaced with 2 horizontal baffles on the basis that vertical ones might be resisting the flow of water a bit.

Increased the size of the pipes and in an out fittings from half inch to 1 inch.

Bench tested the engine including pressure test and confirmed that water was flowing around it well, the head and head gasket were fine and generally that the engine was in very good condition.

Temporarily restricted the flow of water to the califorier to see if that helped.

 

I think that's everything! I've only just had much of this work done so have yet to test it out on the open water, but running it under load but tied up it does seem to have improved it slightly but only in that it now takes longer to reach 100c (about half an hour after engine has warmed up rather than 5 minutes after like it used to be), and seems to stay at around that temperature for longer rather than wanting to go above it. I didn't want to risk running it any longer than that but now I know that I can run it up to 105c (as a one off rather than regularly) without damaging the engine, then I'm going to try it for longer to see if it will want to go above the 100c or stays there.

 

Hope all this makes sense as I'm not a mechanically minded person and struggle understanding it all at times.

[MtB]

Blimey, and your initial post seemed like just an initial curiosity about the high temperature.

 

Given the temperature returned by the gauge is only measuring temperature at the sender, I'd be attaching K sensors and a digital thermometer all over the engine, hoses etc to gain an understanding of the temperatures everywhere.

 

In particular I'd start by measuring the pipe temperatures in and out of the skin tank. Both the difference and the absolute temperatures will tell you loads about what is going on.

[FadeToScarlet]

An infra red thermometer will be your friend here. I love playing with mine, it gives you so much knowledge about what is happening all over the engine and skin tank.

[MtB]

An infra red thermometer will be your friend here. I love playing with mine, it gives you so much knowledge about what is happening all over the engine and skin tank.

 

How do you know it works? All those I've ever owned can be anything between spot on and wildly inaccurate. I've found them less than useless.

[dmr]

 

How do you know it works? All those I've ever owned can be anything between spot on and wildly inaccurate. I've found them less than useless.

 

I find them ok but not super accurate, main error is that they do really badly with a shiny surface so no good for copper pipes. Good for stove and stove flue temperatures. Lovely things to play with. Have observed that the lining on the side of the boat facing the sun gets quite a bit hotter than the other side, that the dogs legs are colder than her body, and that beer in the front locker is 6 degrees in winter but can easily to get to 14 on a sunny day. Hours of fun

 

..............Dave

[cuthound]

How do you know it works? All those I've ever owned can be anything between spot on and wildly inaccurate. I've found them less than useless.

For most purposes they do not need to be massively accurate, they are good for looking at trends a day comparisons.

 

I also find mine is useful for pointing at speeding boaters. One asked me what I was doing. I told him it sent a speed reading, image of the boat and gps position to CRT.

[MtB]

For most purposes they do not need to be massively accurate, they are good for looking at trends a day comparisons.

 

 

I disagree. Those I've used can give readings many degrees apart on two different surfaces known to be the same temperature.

 

If they consistently gave readings say 5 degrees high that would be fine for the purpose you describe (but not others!), but they don't in my experience. They are, or used to be, no more than toys.

[cuthound]

Used to use them all the time when commissioning generators or chilled water systems without problems, for which they had to have calibration certificates, however they were "top end" equipment.

 

I use one I bought of eBay on the boat for £25 or so. It is consistent in its readings but who knows how accurate it is.

[MtB]

Used to use them all the time when commissioning generators or chilled water systems without problems, for which they had to have calibration certificates, however they were "top end" equipment.

 

I use one I bought of eBay on the boat for £25 or so. It is consistent in its readings but who knows how accurate it is.

 

 

Ah now that's interesting. The cheapie ones have NO consistency, which is why I've found them less than useless. I'll try and find one with a calibration stifficate.

 

I'd like to find one that actually works. Happy to pay decent money but only if its gonna flippin' work!

[cuthound]

Ah now that's interesting. The cheapie ones have NO consistency, which is why I've found them less than useless. I'll try and find one with a calibration stifficate.

 

I'd like to find one that actually works. Happy to pay decent money but only if its gonna flippin' work!

This was a popular model.

 

http://uk.rs-online.com/web/p/products/7644405/?grossPrice=Y&cm_mmc=UK-PLA-_-google-_-PLA_UK_EN_Test_And_Measurement-_-Temperature_Measurement&mkwid=sVbActeQF_dt|pcrid|88057067403|pkw||pmt||prd|7644405&gclid=CjwKEAjw1Iq6BRDY_tK-9OjdmBESJABlzoY7AzFUFg26dM4RXoNPvehwVjoBUu05lW1_nY_8Ss3a2xoCUcjw_wcB

 

Too much for me to justify for a plaything on the boat ?

 

Edited to add the last sentance.

Edited May 23, 2016 by cuthound

[Bod]

Thanks all of you for your advice.

 

The temperature gauge and thermostat have recently been replaced together with the sender units. The temperature has been checked and it matches what the gauge is reading.

 

I've had the boat 3 years and it's now 20 years old. I didn't really notice the high temperatures until last June when I went on the Trent and Ouse rivers. Before that I'd just done canals and therefore worked the engine much less. Since then it seems to be worse but I can't be certain of this.

 

Here's what else has been done;

 

Checked water pump is working okay.

Had gearbox checked and reconditioned.

Fitted a header tank 1 metre above the engine (inside the cabin).

Measured skin tank and confirmed it's large enough. I can't remember the size (7ft x 20 inches???) but it satisfied the equation for the hp.

Cut large section out of skin tank out which revealed 4 baffles which were vertical (unusual???) with a half inch gap top and bottom of each one. More sludge found to be lying in the bottom of the tank. The vertical baffles were removed and replaced with 2 horizontal baffles on the basis that vertical ones might be resisting the flow of water a bit.

Increased the size of the pipes and in an out fittings from half inch to 1 inch.

Bench tested the engine including pressure test and confirmed that water was flowing around it well, the head and head gasket were fine and generally that the engine was in very good condition.

Temporarily restricted the flow of water to the califorier to see if that helped.

 

I think that's everything! I've only just had much of this work done so have yet to test it out on the open water, but running it under load but tied up it does seem to have improved it slightly but only in that it now takes longer to reach 100c (about half an hour after engine has warmed up rather than 5 minutes after like it used to be), and seems to stay at around that temperature for longer rather than wanting to go above it. I didn't want to risk running it any longer than that but now I know that I can run it up to 105c (as a one off rather than regularly) without damaging the engine, then I'm going to try it for longer to see if it will want to go above the 100c or stays there.

 

Hope all this makes sense as I'm not a mechanically minded person and struggle understanding it all at times.

 

100F or 100C

Makes a difference.

 

Bod

[Tony Brooks]

 

100F or 100C

Makes a difference.

 

Bod

 

nicely spotted.

[Grassman]

100c (as I mentioned in both my posts )

[Bod]

What are you using to supply the 100c reading?

Any form of independant measurement or just what the gauge is indicating.

Bearing in mind you have a 20 year old boat, with an engine designed decades before, the "correct" gauge may well be calibrated in Fahrenheit.

 

Bod

[cereal tiller]

I have a BMC 1.8 engine and when cruising on rivers or the rare prolonged spells at 4mph on a canal the temperature regularly gets up to 100 degrees C which I was told was the maximum you can safely run a BMC up to without damaging it.

 

It's never been an issue really and at that temperature the engine doesn't seem overly hot (no steam, smell etc). However there may be times on fast flowing rivers where I'd like to give it more power but I haven't wanted to risk the temperature going any higher.

 

Another boater I met recently says that with the correct pressure cap (4lbs according to Calcutt Marine) and a coolant split of 50/50 you can safely run a BMC 1.8 up to 105c before it starts boiling over.

 

He has a chart which gives the maximum temperatures that each strength of pressure cap allows the temperature to go up to and it says a 4lb one is 105c.

 

Any thoughts on this?

A quick question Grassman,does the Boat have a Calorifier,if so how far from the Engine is is sited?

 

CT

[alan_fincher]

What are you using to supply the 100c reading?

Any form of independant measurement or just what the gauge is indicating.

Bearing in mind you have a 20 year old boat, with an engine designed decades before, the "correct" gauge may well be calibrated in Fahrenheit.

 

Bod

 

You have missed this, I think!....

 

 

The temperature gauge and thermostat have recently been replaced together with the sender units. The temperature has been checked and it matches what the gauge is reading.

 

As 100 degrees Fahrenheit is roughly only human body temperature, I'd suggest there is no possibility that Grassman is looking at a Fahrenheit rather than a Centigrade reading, even if they didn't report that the gauge and sender are new.

[Tony Brooks]

From the 2009/10 ASAP catalogue: Standard scale reads 250F main/120C second. For use with American Senders. Metric scale reads 120C main/250F second. for use with European senders so if the OP has a main centigrade scale there is a good chance he needs a European sender.

 

Resistance values of European senders given as 40C - 281 ohms, 80C - 68 ohms, 120C - 22 ohms.

 

However if a US sender is used with a European gauge I would expect the gauge to read less than it should, not more so maybe its mismatched the other way round. US sender resistances: 100F - 450 Ohms, 175F - 99 Ohms, 250F - 29.6 ohms.

 

Until the actual temperature is confirmed by an external thermometer I would certainly measure the sender's resistance to see what type it is. However I have no idea how to confirm the gauge type.

[Grassman]

The temperature has been checked using an infra red thermometer as well as a probe type device. I take your points about the infra red type ones possibly being inaccurate especially the cheaper ones, but the guy who used his to check mine it uses it for checking temperatures of engines (generators) for a 'blue chip' company so I can't imagine it's a cheap one. Both methods indicated that the boat's temperature gauge was accurate.

 

Yes the boat does have a calorifier. The configuration of the pipework has been checked both relating to the calorifier and the skin tank. One suggestion has been to insert a valve near to the calorifier in order to restrict the flow.

 

Re Tony Brook's comment about the correct matching of the temperature gauge and the sender, I ordered both from ASAP supplies so I presume they would have provided me with the proper match?

[Tony Brooks]

The fact that you have confirmed the temperature with two other thermometers means the matching of the gauge and sender can not be the issue.

 

If you think about cars form the age of the basic engine design they all put the cabin heaters in parallel with the radiator, just as the calorifier is normally. Unless the calorifier is plumed in 3/4 ID hose with very short pipe runs I am having difficulty understanding how the calorifier circuit can "short circuit" the skin tank. Before buying and fitting valves put something like a brake pipe clamp on a calorifier feed hoes. If the calorifier is short circuiting the skin thank that will stop it so the temperature should then drop.