Volvo Penta AQ series. Strange tube?

Ira Quirke

Cadet
Joined
Dec 13, 2009
Messages
20
Hi,
And this is directed to any of you guys who have experience with the old AQAD40A engines from VP.
I just did some work on mine and she is still in great condition...redid the turbo and when reassembling the pipes that supply oil and water, one banjo bolt broke.
So off to the dealer and I bought two bolts and the compression washers to suit.
$110.00 for two bolts and four washers?
Anyhow, I was told that the tube which runs from the side of the fresh water reservoir to the side of the turbo (exhaust housing) about 30" away, needs to be primed, filled with water before connection as it can develop an air lock and then, not work............What?

I had a good look at this and it seems to be just a pressure equalization pipe from the one end of the engine to the other.
I am thinking that when the engine is hot and the boat is stopped and allowed to cool, there may be pressure differentials within the cooling system that could put pressure on seals and o-rings so it is good to allow that to equalize.

There is nothing in the manual that refers to this tube and no explanation as to why it is there....it seems that you could probably get away with just plugging the holes and leaving it out......:confused:

For any one that has a problem and can't spend a small fortune on banjo bolts, perhaps this could be a temporary way to run the boat until it can be rectified.

Does any one have any further ideas on this? I don't know if other later engines have a similar tube, Is this the case? Volvo Penta agents don't seem to know what it is either....

If anyone wants some pics I can go out and take a photo....
Cheers, Ira :)
 

louiss3000

Cadet
Joined
Apr 26, 2010
Messages
20
Re: Volvo Penta AQ series. Strange tube?

Although my boat is not powered like yours, mine is a twin AQ130, I do have much experience with Volvo turbo cars. What you're describing sounds like a turbo water cooling line. Many Volvo turbo cars used both oil and water cooling on the turbos. The water line allows cooling after shutdown by allowing water to circulate using the latent heat in the turbo, hot water rises and is replaced by cooler water. Don't leave it off.
 
Top