View Full Version : Need help with impeller AQ125

07-29-2006, 06:30 PM
"I have a 1984 Bayliner Capri with the AQ125. The engine started overheating at idle so I purchased the following impeller:

http://www.marineengine.com/parts/part_details.php?pnum=SIE18-3075&returntopage= ("") 80240420.htm

When I took the old impeller out, the rubber was still in really good condition, but the impeller looks way too big. The fins were smashed into the impeller housing and it wouldn't turn, so I pulled it out and put the new impeller in and it's the same... it won't spin because it's too big. I'm not getting any water out of the exhaust either. Did I order the correct part, or is my engine not the AQ125 like I thought?

I'm really puzzled..."

07-29-2006, 07:08 PM

18-3075 ("") should be the correct impeller for an AQ125 (although if you are not sure that is what you have then I'm not either...).

A rubber water pump impeller is supposed be installed so that it's off-center and the vanes are squashed on one side. Essentially the impeller is trying to compress the water (which the water won't do), but instead displaces the water out the discharge in the direction it is supposed to go.

Here is a picture with a typical "installed" rubber water pump impeller.


El Pescador
07-29-2006, 07:16 PM
"Here is a link to the cooling parts for the AQ125:

http://www.depcopump.com/catalog108/116.pdf ("]http://www.dougrussell.com/partscatalog/volvo_omc/index.cfm?fuseaction=comp&amp;grou p=1868&amp;GroupList=1885,1864,1863,1873,1874,1868,186 2,1861,1865,1884,1883,1867,187 1,1872,1869,1878,1879,1880,1881,1882,1866,1887,187 0,1886,1875,1877[/url]

The pump part number should be 855578, which you can see here:


The Johnson number for the impeller fitting that pump is 09-801B, which means you should have the correct part.

Remember that the impeller fins need to be &#34;smashed&#34; at one side of the pump, but not so at the opposite side. This is how this type of positive displacement pump works. Make sure, however, that when you install the impeller you turn it clockwise so that the fins have the position they would have during normal running."

07-30-2006, 11:13 AM
"Thanks for the info guys! I didn&#39;t know it was supposed to be smashed on the one side. The old impeller&#39;s fins were smashed in both directions, so I put the new one in and turned it clockwise while installing so the fins are all going in the same direction. What makes the impeller turn? The rod that goes through middle of the impeller will free spin without turning the impeller. Is that normal?

I&#39;m still having an overheating problem. I&#39;m still not getting water out of the exhaust and the temp got up to 190 - 200 before I shut it off. I did see the temp drop once while it was at a fast idle, so I&#39;ll assume the thermostat is opening properly. When I shut it off there was white steam coming from the exhaust hose."

07-30-2006, 11:44 AM
The shaft shal NOT fri spin without turning the impeller. Have You forgotten the key or screw that goes in the slot of the shaft when You hanged the impeller?

07-30-2006, 12:44 PM
"Maybe that&#39;s where the problem lies... there wasn&#39;t a key or screw to go in that slot. Would that part be #48 on this diagram?

http://www.dougrussell.com/partscatalog/volvo_omc/index.cfm?fuseaction=comp&amp;grou p=1868&amp;GroupList=1885%2C1864%2C1863%2C1873%2C1874% 2C1868%2C1862%2C1861%2C1865%2C 1884%2C1883%2C1867%2C1871%2C1872%2C1869%2C1878%2C1 879%2C1880%2C1881%2C1882%2C186 6%2C1887%2C1870%2C1886%2C1875%2C1877 ("")"

07-30-2006, 12:53 PM
"Seems like the kit should have had a key as shown in the picture of 18-3075. ("")"

07-30-2006, 12:58 PM
"No. If there is a slot in the shaft, there should be a screw going through the center of the impeller. If there is a key way at the shaft &#40;impeller should look like drawing above&#41; the key may be missing or You have pushed it away when installing the impeller. Been some time since I worked on this unit."

07-30-2006, 01:12 PM
Take out the impeller again and check. Perhaps the old key is still inside but been pushed out.

El Pescador
07-30-2006, 01:55 PM
"84capri, the impeller is meant to be secured to the pump shaft by means of a woodruff key. If the key is not there the shaft will freespin and the engine will not get any raw water. You first have to install the key in the slot, then push the impeller into place. This is better done with the pump removed from the engine."

07-30-2006, 04:53 PM
I checked the box and I do have the key &#40;that looks like a wedge&#41;. There is also a rubber circle piece. Does that need to be installed as well? Does the flat surface of the key need to face the inside of the impeller or the outside?

BTW - You guys are awesome!

El Pescador
07-30-2006, 06:04 PM
"First of all, you should try to find what happened to the key that secured the old impeller, for you dont want it loose in the seawater system.

To install the woodruff key, remove the impeller and place the circular part of the key inside the groove in the shaft. Make sure that the flat part of the key is not completely parallel to the keyway, the innermost part should be slightly higher than the outer; this will facilitate the installation of the impeller, and after you push the impeller into the pump the key will be completely parallel to the keyway.

The rubber circular piece is a plug to cover the end of the shaft; just push it in with your finger once the impeller has been installed."

07-30-2006, 09:14 PM
"The flat rubber washer is only used in pumps where the end of the shaft is even with top of impeller. Your shaft is protruding into the cover &#40;cover act as an extra bearing&#41;, and shall not be used."

El Pescador
07-30-2006, 09:34 PM
"You are right, Morten. I stand corrected, I guess I had in mind the Johnson raw water pump for the 350s and 305s."

07-31-2006, 10:42 PM
I reinstalled the impeller correctly with the woodruff key. I&#39;m still having an overheating issue. When running the motor on the muffs it didn&#39;t look like any water was being sucked into the outdrive so I put the outdrive in a trash can filled with water and I was right. There isn&#39;t any suction at all.

El Pescador
07-31-2006, 10:56 PM
"What is the condition of the raw water hose connector in the outdrive? Disconnect the hose and if the clamshell-like connector is corroded, replace it."

R. Loeffler
08-01-2006, 10:35 AM
"I have found that the cover, and the inner face of raw water housing for the impeller has to be smooth. If there are any grooves in the inner face of the housing or on the cap, even with a new impeller, the water will not be compressed and will deviate around the ends of the impeller. Make sure the impeller cover and housing are smooth and undamaged. I had the same problem with a aq131d. Ended up replacing the raw water pump housing."

08-01-2006, 10:53 AM
"I agree with R.L, but providing no air leaks on the suction side it sometimes help loosening the seawater strainer cover to make the pump &#39;start&#39; if completely dry like after an impeller change. This way there will be no exhaust back pressure against the pump. Just watch out so You do not flood the engine!"

09-05-2006, 04:47 PM
"Is the impeller the water pump, or is there a seperate water pump? I looked through my manual but the only thing it shows is the impeller housing as the sea pump. Which part provides the suction from the outdrive to the impeller?"

El Pescador
09-05-2006, 05:04 PM
"The impeller we are talking about is the rubber part inside your sea pump that causes the water to flow from the outdrive to the pump via the rubber hose and copper pipe, and then from the pump through the heat exchanger and the exhaust manifold. Whent he impeller turns, it pumps the air out of the pump towards the heat exchanger and creates a vacuum that makes the water frow from the outdrive to the pump."

09-05-2006, 05:21 PM
Thanks for explaining it! Since I&#39;m not getting any water in the impeller housing there has to be an air leak somewhere.

El Pescador
09-05-2006, 05:32 PM
"Did you check the condition of the raw water hose connector in the outdrive? It looks like this:

http://www.dougrussell.com/partscatalog/volvo_omc/index.cfm?fuseaction=comp&amp;grou p=1842&amp;GroupList=1852,1824,1893,1892,1891,1890,184 0,1841,1842,1888,1889,1821,182 0,1822,1823,1853,1851,1834,1835,1894,1837,1838,183 6,1854,1839,1833,1844,1847,184 9,1845,1850,1825,1856,1857,1828,1830,1831,1832,182 9,1826,1827,1855,1843,1846,184 8 ("]http://www.marineengine.com/parts/part_details.php?pnum=SIE18-2778&amp;returntopage= 80240788.htm[/url]

It is part 79 in this page


Disconnect the hose and if the clamshell-like connector is corroded, replace it. Corroded hose connectors are one of the major causes or air ingress in the cooling system."

09-05-2006, 07:23 PM
Thanks again El Pescador. The raw water hose connector is really corroded. I just ordered a new one. After reading the symptoms of other people I&#39;m pretty sure this will fix my problem as well. Thanks again!

PS - Should have checked it the first time.