Volvo AQ171/SP Overheating

[sabotobu]

Hello, <br />I just bought a 1991 Imperial with either a 91 or 92 Volvo Penta AQ171/SP engine. It is a 251 DOHC 4-cylinder, 16-valve, 4-stroke with 167HP crankshaft and 150HP propeller shaft power.<br />We just had the boat tuned up, and it seems to get up to speed very well.<br />However, when we start going over 2500 RPM the temp and oil gauge both show the engine is hot very quickly. I do not know a ton about engines, and was wondering if there is anything I could try.<br /><br />Thanks for any help you can provide

 

[Dunaruna]

Re: Volvo AQ171/SP Overheating

Hi sabotobu,<br /><br />You've got a rare beast there, that motor is highly sort after by amateur rally drivers.<br /><br />First thing to check is your raw water supply. All of the following should be part of a regular maintanence schedule.<br /><br />-Raw water impeller (front of motor). <br />-Raw water seaweed screen (intake side of heat exchanger)<br />-Flush out heat exchanger.<br /><br />Is the closed side clean & full (no leaks)?<br /><br />Many more things you can check but do the basics and see how it goes. Good luck.<br /><br />Aldo

 

[sabotobu]

Re: Volvo AQ171/SP Overheating

Thanks for the reply.<br />I was just out looking at it, and the seaweed screen is clean and clear. I looked at the impeller, the first time I've seen one, so I'm not 100% sure what it was supposed to look like. However, I think at least one of the fins was damaged. Is there any easy way to tell if the impeller is working? <br />I'm not sure how to fluch out the heat exchanger. <br />I did open the valve at the bottom of the oil cooler and the water that came out looked clean.<br />The closed side seems fine. Plenty of antifreeze, and I have not noticed any leaks at all.<br /><br />Thanks for the help!!

 

[Dunaruna]

Re: Volvo AQ171/SP Overheating

If one blade looks damaged then its a fair bet its due for replacement. Also check the impeller housing for damage, sand can score the surface.<br /><br />To flush the raw water side of the HE, disconnect both raw hoses (inlet & outlet) and use your garden hose to flush it out. Flush it reverse to normal flow. The seaweed mesh filter won't stop crud from building up inside the HE. You can flush the oil cooler the same way.<br /><br />Raw water pumps can be flow tested but I wouldn't reccomend it unless you are confident. Some people test them on the muffs but that gives a false result, its best just to replace it at reccomended intervals as you would spark plugs, oil & filters etc. Its cheap insurance.<br /><br />Most important, never run the impeller dry, it the biggest killer of raw water pumps.<br /><br />Aldo

 

[sabotobu]

Re: Volvo AQ171/SP Overheating

Thanks a lot! I'll try that this weekend.

 

[Dunaruna]

Re: Volvo AQ171/SP Overheating

This is a generic drawing of an impeller, it may not be exactly like yours but its good enough for an example.<br /><br />

<br /><br />If any or all of the blades are damaged - its no good. If its lost its flexibility - its no good.<br /> If a piece is missing it could be lodged in the cooling system somewhere.<br />Aldo

 

[sabotobu]

Re: Volvo AQ171/SP Overheating

After looking at the impeller again, I'm pretty sure that is the main problem. <br />Just so I'm 100% sure about how to do it, should I be able to just pull the impeller out of the housing and slide a new one in, or are there additional parts I need to replace?<br />I also plan to flush out the rest of the system as well as I can. Hopefully that will take care of my problems.<br /><br />Thanks again.

 

[Ed Polguy]

Re: Volvo AQ171/SP Overheating

I have 2 off those nasty beasts on the back my Imperial, and both had overheating problems. <br />heres the list;<br />1. raw water pump was worn out on the port engine,<br /> pump was sucking air though a bad seal,<br /> got a re-bulid kit ( $350.)<br />2. had the manifolds boiled out, found a crack in<br /> the starboard man. got it welded.( 270.00)<br />3. Starboard engine boiled over, tried the raw <br /> raw water pump fix, n.g.I found the pick up hose came of of the flange on the hinge bracket.<br /> The engine ran fine at idle speed , but would overheat on plane, because the hose was not picking up water but air.<br /> off of the flange