Isuzu 42 running too cool 45C even with new themostat.

[rogerc]

Hi everyone

i have an Isuzu 42 engine in my 65 ft boat; for many years it has run at 85C, but last autumn it was running about 45C. i have checked the temps with a thermo gun and the heat is going into the side tanks so i assumed the thermostat was sticking open and fitted a genuine new one, but the problem persists. i checked both thermostats and they open at about 85C. if i clamp the pipe to the side tank the temp rises to over 90C. so it appears that some how something has changed that lets water past the thermostat!

has anyone any suggestions, please?

thanks Roger

[Tony Brooks]

How long did you run for? The calorifier normally, but not always bypasses the thermostat so the engine temperature will not rise until the calorifier is hot.

 

If its a twin coil calorifier it is possible a wet central heating system is thermo-syphoning drawing heat from the calorifier into the radiators - or a circulating pump may have been left on.

 

But as it seem you are an experienced boater neither is likely.

Edited March 16, 2016 by Tony Brooks

[rogerc]

thanks Tony

heat is being drawn off to the calorifier but it is also going to the side tanks at 45C and probably at lower temperatures too

[Bee]

Strange, I think I would take the stat out then run it and see what happens, might not give an answer but it might give you something else to work on.

[Dalslandia]

How is the temp mesurad? checked!

is the instrument OK and probe ok. the probe have a ohm stamped or listed. checked!

did you "boil" check the old thermostat? checked!

is the new mounted the right way? was the old the wrong way, and the new got in the same way? (should get hot though)

can you block, or just recycle the calorifier hose back to engine and re-test? checked!

Is the calorifier spiral leaking inside?

Edited March 16, 2016 by Dalslandia

[rogerc]

i have thought of running it with a blanking plate in place of the thermostat to confirm there is an alternative path.

temp measured several ways and all agree. the old stat worked for the first 5 years i have had the boat till last autumn.

[Bee]

Odd innit, if you clamp the pipe to the tank the temp rises, that's logical, it restricts the flow, yet the stat isn't doing the same job by restricting the flow. It should do. I think I would be suspicious of the stat.

[blackrose]

Hi everyone

i have an Isuzu 42 engine in my 65 ft boat; for many years it has run at 85C, but last autumn it was running about 45C. i have checked the temps with a thermo gun and the heat is going into the side tanks...

 

You have two skin tanks? It might be a workaround solution, but why not just plumb the cooling system through one tank only and just drain the other?

 

Most of us with engine cooling issues have had the opposite problem and have had to install an extra skin tank or use some other method to cool the engine adequately. Your problem might be easier to solve.

 

Edit: Actually, thinking about it I'd probably leave the unused skin tank full of antifreeze/coolant to prevent internal corrosion.

Edited March 16, 2016 by blackrose

[bizzard]

It does sound like a thermostat problem. It might not be locating properly in its recess or something and being by-passed enough to reduce the overall temperature of the system coolant. There is something to try though. There are car thermostats that simply poke into the top outlet hose as close to the engine as possible. As I said these thermostats have a cylindrical body and just poke, with slight resistance just inside the top hose and are held in place with a hose clip around the outside of the hose.

Certain older cars used this type. Volvo 340 B14 and some Renault engines for example. It of course will depend on the inside diameter of your top hose for the right fit. There are thermostat suppliers websites, so perhaps a measure up and check them out. I would remove the existing first if you decide to go this route. I have an old Volvo 340 thermostat of this type knocking around somewhere which I could measure for you if you wish.

[alan_fincher]

It does sound like a thermostat problem. It might not be locating properly in its recess or something and being by-passed enough to reduce the overall temperature of the system coolant.

 

I agree that it sounds like the thermostat is simply not doing its job, but the odd think reported is that a genuine replacement has been tried with no improvement.

 

Also that both the stats behave as expected if tried independently.

 

To not be bettering the temps quoted, it sounds like you might get if there was no stat at all, or that it were permanently open. Further the fact that claming the pie is the only thing that pushes the temperature up would appear to say the same.

 

You have got me beaten at the moment, as you appera to have looked at and correctly ruled out the obvious.

 

I know some engines can have thermostats that are either "long reach" or "short reach", and that fitting the wrong one can stop them working. Is the new one you are trying dimensionally the same as the original?

[blackrose]

When I worked in the boatyard and was thinking of changing the thermostat to rule that out of my overheating issues, one of the engineers told me to drill a 1mm hole in the thermostat. But I can't remember what that was for?

[alan_fincher]

When I worked in the boatyard and was thinking of changing the thermostat to rule that out of my overheating issues, one of the engineers told me to drill a 1mm hole in the thermostat. But I can't remember what that was for?

 

Probably to allow air to be able to pass through it, even when shut, but not enough water to pass in normal operation to hamper the stat's function? Old stats used to have a somewhat larger hole drilled in, bit with a little "bobble" on a captive "stalk" that would cover the hole when the pump was pushing water through.

 

The reason is to stop air locks, and to be able to fill the system fully in a way coolant will get everywhere it needs to. Modern stats often have no hole, and hence air locks are more likely.

 

However, as you say, not having this might result in overheating, but I can't see how it would result in under-heating to the degree shown here. If there is an unimpaired hole through the stat, a small amount of water will be pushed through it, even if the stat is closed, but I can't imagine it being enough to keep the engine temp that low.

[bizzard]

When I worked in the boatyard and was thinking of changing the thermostat to rule that out of my overheating issues, one of the engineers told me to drill a 1mm hole in the thermostat. But I can't remember what that was for?

Some thermostats do have the hole, with a little wiggler in it. The hole makes it easier to bleed out air from the engine whilst the engine is getting up to heat and also makes it easier to fill or top up when cold as air will gradually be expelled through it and up to the filling point and away out, with a bit of luck.

[blackrose]

What about my idea of just using one skin tank (assuming the boat has two)? I realise it's not getting to the bottom of why the engine is over-cooling, but wouldn't it raise the engine temperature and solve the problem?

[bizzard]

What about my idea of just using one skin tank (assuming the boat has two)? I realise it's not getting to the bottom of why the engine is over-cooling, but wouldn't it raise the engine temperature and solve the problem?

It would probably raise the temperature, yes, but by how much, who knows, and one tank might be too small and cause overheating after a time.

If the tank was as big as and held as much water as the Atlantic ocean the thermostat should still control and keep the coolant in the engine at normal recommended running temp.

[blackrose]

It would probably raise the temperature, yes, but by how much, who knows, and one tank might be too small and cause overheating after a time.

If the tank was as big as and held as much water as the Atlantic ocean the thermostat should still control and keep the coolant in the engine at normal recommended running temp.

 

That's true, it's difficult to know how much it would raise the temperature, but there's only one way to find out... The engine might overheat, it might still be too cold or perhaps it might be just right. But if it's not tried we'll never know.

Edited March 16, 2016 by blackrose

[ditchcrawler]

 

That's true, it's difficult to know how much it would raise the temperature, but there's only one way to find out... The engine might overheat, it might still be too cold or perhaps it might be just right. But if it's not tried we'll never know.

Surly that's a bit like having a faulty kettle so you ware rubber gloves not to get a shock

[Dalslandia]

One thought.

 

1. was any changes made just before the engine started to run cold?

1.5. does the engine get warm and then cool of when the termostat open?

2. is there a a missing gasket under or over the termostat so it can lift by pump pressure?

some have a rubber gasket, some don't, some thermostats is "double" valve, so it close the recirculation internally when open fully, can it get stuck in something.

3. I don't know what it is, but something it must be.

One or two tanks, should not effect the problem it self.

[blackrose]

Surly that's a bit like having a faulty kettle so you ware rubber gloves not to get a shock

 

No I don't get your analogy at all. There is no imminent danger in only using one tank as far as I'm aware.

 

I suggested using one skin tank as a workaround - simply in order to be able to move the boat for the time being if required. I wasn't suggesting it as a permanent solution.

Edited March 17, 2016 by blackrose

[Neil Smith]

Only an outside chance but could one of the skin tanks have rusted through and is sucking in canal water.

 

Neil

[Dalslandia]

Only an outside chance but could one of the skin tanks have rusted through and is sucking in canal water.

 

Neil

 

Should not change anything, if the thermostat work as it should

[rogerc]

thanks for all your replies. there are no significant leaks, and i cant think of any significant events prior to noticing the problem. i dont want to pursue the single side tank option as it might not make much difference except if i were going against the flow on some occasion and might regret it.

 

i will take it apart again next week and see if there is any obvious reason why water should bypass the thermostat. if not i will block/blank off the thermostat and see if that stops the flow. if it doesn't and i cant find why i will adopt Bizzard's solution of fitting an inline thermostat.

 

if anyone else has any other suggestions please continue to contribute

[smileypete]

Does the pipe downstream of the thermostat get warm when underheating occurs? If not then there's no flow getting through, toward the skin tank presumably.

 

If all else fails maybe try drawing a diagram of the system, could even label it up with temps in different places when the underheating occurs.

 

cheers, Pete.

~smpt~

Edited March 19, 2016 by smileypete

[rogerc]

hi

i thought i should report what i discovered.

i decided to remove the thermostat and replace it with a blanking plate. i have 2 calorifiers connected in series with a heater element from a van heater (fan not running). At the start the side tank temp was 10C, the engine and calorifier 12C. it took 40 minutes for the temperature to reach 84C (temp the thermostat would open) with the boat moored up in gear at ~1300RPM the temp gauge read 76C (8 C low) and return from the calorifiers was 66C and the hot water was now ~45C. as expected the supply pipe to the side tank only rose a couple of degrees.

i then drilled a 2mm hole through the blank plate. and tried again the side tank still 12C, engine 33C, Calorifier ~ 42C. after 5 minutes the water to the side tank was heating up and about 5c less than the engine temp this difference extended to 8C until the thermostat opened after 55mins.I discovered the best way to tell wen the thermostat opened was to feel the return from the side tank as it returned to the engine which suddenly changed to cold.

so i discovered that winter running with a really cold calorifier is significantly different from summer running that i am used to. and that the 2 mm vent hole in the thermostat allows a considerable flow of water cooling the engine. so i refitted the thermostat with a 1mm bolt through the hole (reducing the flow by 25-40%). when i ran the engine a week later i didn't do any specific measurements but it took 65 mins for the temp gauge to steady at 76C when the thermostat opened. last summer this typically took 40 mins with a 2mm hole.

so the little hole allows a significant flow and the calorifiers provide a significant cooling effect until they heat up. when i next drain the engine i will further restrict the hole. i suppose side tanks probably provide much less resistance than a small van radiator.

 

thanks for all your suggestions.

Roger

Edited April 24, 2016 by rogerc

[Bee]

Thanks for telling us, always nice to know as sooner or later someone else will get the same problem. Biggest problem is probably oil temp and sludge forming but I'd hazard a guess that a lot of boat engines take a long time to get warm, mine does but the oil always seems ok whenever I change it.