Volvo penta 2001 overheating alarm

[warrenmarkus1]

On a long run today, with the engine at about 60% throttle, the engine overheat alarm sounded. Their was water coming out of the exhaust (sea water cooled) and no steam, and the head was hot.
Throttling back the engine, the alarm went out. 30 mins or so later when we increased the engine speed the alarm went off after a short while, again there was water coming out of the exhaust, and no steam. Again throttling back caused the alarm to switch off.
A blockage in the raw water intake, or damaged impeller, or stuck thermostat would cause the would cause the head to get hot enough to vapourise the water giving steam in the exhaust - which has happened in the past when the inlet water strainer got blocked.
But having water in the exhuast, and the engine over heating has me stumped!!
Suspect sender unit perhaps - but how do you check it?
Any ideas gratefully accepted!!

 

[finns]

Until last summer I had a VP 2001. Some years ago it developed symptoms that were very much like those you describe.
The engine performed well with low load. High loading made the temperature alarm sound. I checked water intake, water pump, thermostat, cooling jacket on exhaust manifold etc. Everything seemed to be ok.
When doing some other work on the engine I disconnected the cooling water inlet on the block (in front of the engine) and the "by-pass" outlet to the exhaust (at the rear). To my surprise there was a clean, straight pipe between the two!
After scratching my head a few times, I decided that there had to be a hole somewhere along this pipe, that should lead water into the cooling jacket around the cylinder. Looking into the pipe, with a torch illuminating it from the other end, I found a dark patch. Using a bent steel wire I was able to re-open what had been a hole - and the cooling system was back in business!

 

[VicS]

If you are absolutely sure there is a good water flow from the exhaust then the problem could be due to scaling or corrosion of the engine waterways restricting the flow of water through the engine.
It could also be due to the thermostat not opening correctly.

Inlet, strainer and pump impeller if not newish are always the first things to check though.

The water in the exhaust at the same time as the engine overheating is possible as water will always flow to the exhaust to cool it even if the flow through the engine is restricted or if the thermostat fails to open.

 

[1955patric]

You don't say whether your engine is direct or indirect cooled. However on my VP 2002 indirect cooled engine I had a similar problem a couple of yeras ago. I checked the impeller & strainer and tested the thermostat and sender and could find nothing wrong with them so opened up the heat exchanger and found it badly scaled. I cleaned it using central heating descaler ( Furnox) and have had no problems since. It sounds to me as if you may have a similar problem. If your engine is raw water cooled, as VicS says, it could well be scaling of the waterways in the block and head causing the problem.
I would test the thermostat first and if it is not that look to descaling.

 

[VicS]

I've no first hand experience of the engine but that hole has to be correctly orientated i belive if the pipe is removed and refitted..

Workshop manual

 

[chrishelen]

They are direct raw water cooled, the waterways in the heads are prone to salting/silting up, if you take the anode out( its on the front of the head) and have a look inside and have a poke around with a bit of wire it might become a bit clearer as to whats happening.

 

[davidportwain]

I'm getting the overheat alarm sounding on my (new last year) Volvo penta D1-20. I've checked the impeller (changed this summer) and with the thermostat removed I still get it. Any suggestions?
I would like to check out the temperature sender but dont know where it is.
Also how can I check the freshwater pump?
Does anyone know of a website for a munual on this engine?

 

[bendyone]

[ QUOTE ]
You don't say whether your engine is direct or indirect cooled. However on my VP 2002 indirect cooled engine I had a similar problem a couple of yeras ago. I checked the impeller & strainer and tested the thermostat and sender and could find nothing wrong with them so opened up the heat exchanger and found it badly scaled. I cleaned it using central heating descaler ( Furnox) and have had no problems since. It sounds to me as if you may have a similar problem. If your engine is raw water cooled, as VicS says, it could well be scaling of the waterways in the block and head causing the problem.
I would test the thermostat first and if it is not that look to descaling.

[/ QUOTE ]

A good few years age there was a design fault with this hole in this pipe. It was too small, ours was drilled out by Volvo eng to sort the problem,

 

[Jabberwock]

If the engine is fresh water cooled a blockage in the small pipe from the thermostat housing to the fresh water resevoir can cause an airlock and an overheating cylinder head. I had an intermittent overheating problem for a long period eventually traced to an overtightened clamp pinching the upper end of this pipe where it fed into the resevoir. More common is a blockage in the small orifice at the thermostat end.

 

[warrenmarkus1]

Thanks to one and all for your posts. The engine is direct sea water cooled (no exchanger).
I was thinking if the head water passages were blocked, and the engine was genuinely hot it would boil the water giving steam in the exhaust??
Hence my suspecting the sender unit as faulty.
Still, I will try some of the ideas mentioned the next time I am on the boat.
Thanks

 

[RedAdmiral]

The problem is well known. The transfer pipe passing through the head needs to be driven out from the front - it comes out at the rear at the connection to the exhaust mixer box. The pipe has a number of holes (depending on model of engine) which allow a certain proportion of the cooling water passing through to the exhaust to be bled into the head and rest of engine. These holes get blocked - hence the overheating of the engine without any other symptons. On my 2002 I fixed the problem some 5 years ago by drilling out the holes to 6mm. No problems since.

 

[Rustyknight]

I had the same trouble a few years ago with my 2001. Because I was advised that it's easy to damage the pipe whilst knocking it through the block (pays to select the correct sized drift!) I replaced the old with new.

Here's a pic of the one that came out.

The build up of crud can clearly be seen along the length of it, as can the single hole that allows water into the engine block. When re-fitting, this hole must point downwards!