Can you touch a hot engine block ?

LONG_KEELER

LONG_KEELER

Well-Known Member
Joined
21 Jul 2009
Messages
3,720
Location
East Coast
Visit site
Just wondering if there is some kind of rule of thumb among engineers to tell if an engine is too hot or not.

I have a bog standard Volvo 2001 raw water cooled diesel. I have no rev counter or temperature gauge.

Above about half throttle, the overheating alarm goes on. Copious amounts of water are coming out of the exhaust which only feels luke warm.

I have tried the thermostat both in and out - no difference.

Any thoughts ?

Thanks in advance.
 
There have been a number of threads on this problem. The cause is normally the scaling and partial blockage of the brass tube passing through the cylinder head. Cooling water from the pump is fed to this tube at the front of the engine, passes through the tube and is then fed into the exhaust mixer at the back. The engine depends for its cooling on the small flow of water which is bled through holes in the side of the brass tube. These holes are small and get blocked. Many folk drill them out to a larger diameter.

The tube has to be driven out of the rear of the head by using a suitable drift at the front after uncoupling the water pipes at each end. It's not as complicated as it sounds but it's probably wise to buy a new brass distribution pipe which for the 2001 is part number 840842-9 so you can see drift diameters before you start.
 
You should be able to touch the cylinder block or head of a sea water cooled engine and maintain finger contact briefly.

You should be able to touch a fresh water cooled engine too but not maintain finger contact for long.

It depends on how tough your skin is and how used you are to handling hot objects.
 
Red Admiral said:
There have been a number of threads on this problem. The cause is normally the scaling and partial blockage of the brass tube passing through the cylinder head. Cooling water from the pump is fed to this tube at the front of the engine, passes through the tube and is then fed into the exhaust mixer at the back. The engine depends for its cooling on the small flow of water which is bled through holes in the side of the brass tube. These holes are small and get blocked. Many folk drill them out to a larger diameter.

The tube has to be driven out of the rear of the head by using a suitable drift at the front after uncoupling the water pipes at each end. It's not as complicated as it sounds but it's probably wise to buy a new brass distribution pipe which for the 2001 is part number 840842-9 so you can see drift diameters before you start.
Click to expand...

Had this problem on 2 engines ( catalac 9M ) back in the 90's fixed by Volvo FOC in St Peter Port. The hole in the pipe was enlarged.
 
The raw water cooled engine should be below 50 / 60C. The fresh water should be about 90C which is too hot to touch in my view.

The 2000 series has a very funny water flow. Most of the cooling water flows through the block but then bypasses the cylinder head and goes direct to the exhaust. Flow through the head only occurs when the thermostat opens and even then it doesnt shut off the rest of the flow through the block. So you can get an apparently good flow of water with the cylinder head overheating for the reasons stated by Red Admiral.
 
On a more general note, one of those infrared thermometers can be v.useful for checking the engine the temperatures on different parts of an engine. I tend to use one to regularly check the temps at the top of each cylinder, fresh and raw water in and out, and, pullely/belts temps. Well worth a £20 investment IMHO.
 
Many thanks for the responses.

Some excellent ideas and thoughts as usual.

It is interesting that this problem surfaced in May of this year.

I dismantled and cleaned the exhaust elbow. I poured Cementone ( mainly hydrochloric acid) into every crevice of the water system of the engine.

I cannot tell you how much crud there was in the elbow and other places. I had a fizzing time, and everything visible looked beautifully clean.

The drilling through the head which has been mentioned was clogged. The Cementone cleared most of the crud, and I gently pushed a correct thickness long rounded screwdriver shaft all the way through. I could see daylight all the way through.

Upon recommissioning, the water flow is, and was, stupendous compared to previously. So I am a bit stumped as to what to do next.

When the engine is hot, the exhaust elbow is cool by touch , the area around the thermostat housing seems hotter that most other places. The temperature sender is just underneath this area.

My gut feeling is that water is going through the drilling in the head satisfactorily ( although I could be wrong) but the majority then just going to the elbow and out. Hence lots of water but very cool.

I feel that water is not getting to the other places which it should reach but have no idea what to do next to clear them. When I pour water into the thermostat housing it passes through to the drain plug underneath with good flow.
 
Have you changed the sender unit for the overheat alarm? Had the same frustrating problem with my Yanmar. New sender cured the screaming - was nothing wrong with the water flow as I had done similar cleaning out.
 
With respect, I think you misunderstand what I and others posted. What you call the drilling through the head is a removable brass tube which has holes drilled in the side of it to allow cooling water to flow into the head/block when the thermostat opens. IMHO you will have to drive out the tube as previously suggested in order to clear/drill out the small holes in the tube. I have found that nothing else works.
 
Red Admiral said:
With respect, I think you misunderstand what I and others posted. What you call the drilling through the head is a removable brass tube which has holes drilled in the side of it to allow cooling water to flow into the head/block when the thermostat opens. IMHO you will have to drive out the tube as previously suggested in order to clear/drill out the small holes in the tube. I have found that nothing else works.
Click to expand...

Ah............

Thanks Red Admiral.

That's excellent . Did not know that it had holes drilled in the side. That explains it.

Now understand previous search's where it is wise to mark the tube/block to correctly position the holes.

Might as well renew the sender at the same time as drifting the brass tube out.

Now feel I'm on the right path.

Many Thanks.
 
Just some feedback on the problem.

Re: Cooling alarm on Volvo 2001 raw water diesel.

As mentioned, although the water distribution tube running through the block was clear, and plenty of water in the exhaust, the alarm would come on.

It was clear that the distribution tube was going to be very difficult to drift out . I decided to leave this to an marine engineer.

As often happens, he did not turn up.

On further searching on these forums, it became clear that there was only one hole in the tube leading to the engine galleries etc. Multiple cylinder 2000 series have more.

I shone a torch at one end of the tube with a mirror at the other. No holes could be seen easily. A knitting needle was put in a vice , the end being bent at right angles, just big enough to go in the tube.

After some considerable time I felt the hole . After some generous prodding there was every chance the hole was clear.

I checked all other orifices in the system and gave it another dose of Cemontone Brick & Patio Cleaner.

Test ran the boat today at sea and everything is now working fine.

Many thanks to all for their very useful advice.
 
scottie said:
Should be two holes per cylinder one vertical down into the block the other horizontal to the injector sleeve
Click to expand...

Thanks for the heads up. Have valued your input on this forum over the years.

Ed Essery of this parish only managed to find one I think.

The one I found was in about the six o'clock position.

Will definitely have another poke around.
 
VicS said:
You should be able to touch the cylinder block or head of a sea water cooled engine and maintain finger contact briefly.

You should be able to touch a fresh water cooled engine too but not maintain finger contact for long.

It depends on how tough your skin is and how used you are to handling hot objects.
Click to expand...

Maybe to the first since the usual rule of thumb is that the max temperature you can stand is 60C and then only instantly and the working temp of a raw water engine is around 50 to 60. But if you can touch a fresh water cooled engine running at 90C and not yelp in pain you are a better man than me Gunga Din! Its enough to cook your fingers - literally.
 
scottie said:
Should be two holes per cylinder one vertical down into the block the other horizontal to the injector sleeve
Click to expand...

I managed to get this from Volvo.

As far as I can see, there is only one hole for the 2001, but two for each cylinder as you have mentioned for the bigger engines.

dist_pipe.jpg
 
You must log in or register to reply here.

Share this page

Top