Opinion on 1976 Merc 888 cooling issue

[JasonB]

I replaced the impeller and tstat on my 888 and it dow does something odd. When running it saturday, it idled perfectly at 140 degrees. While running on plane, it was up to 165, which is odd, and after shutdown for 10-15 min, it had heat-soaked to 180-185. At this point it wouldn't idle for anything and was hard to start. I guessing due to heat soak in the carb evaporating the fuel in the bowls. When it did start, the temp would hover at 160 while idling for quite a bit before it would cool back down.<br /><br />This afternoon, I put a big tub under the outdrive, filed it to above the intakes on the drive with water (hose still running) and started it up. Warmed up to 140 and held just as it should. Put my hands around all 6 hoses on top, and after the tstat opened at 140, they were all hot to the touch and it seemed I could feel something like water bubbles in them, not just water flow. I also see am anount of steam coming out the exhaust relief holes in the transom housing even though water shoots out 2' or more to either side at idle. all hoses/clamps are good/tight. I'm suspecting something in teh inpeller job isn't right. Anyone have any educated thoughts before I pull it back apart?<br /><br />Manifolds are less than 3 years old, freshwater only boat. Probably has less than 50-60 hours on new engine/manifolds/risers.

 

[Haut Medoc]

Re: Opinion on 1976 Merc 888 cooling issue

Just a guess....Blown head gasket?....It's the steam thing that makes me think this, and the above normal temp at high rpms....If were fwc it would be easy to check, I'm not sure how to check it with rwc.....JK

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

Would a compression check adequately show a leaky head gasket? I guess I could look at the plugs to see if any are too clean. It's just odd since it idles perfectlya nd runs great until it warms up, at which point, when running say 2500 and over 160 deg, it acts like there is a miss occasionally. I've been wondering if I should pull the valve covers and re-torque the heads.<br /><br />Everything seemed fine until I did the wp/tstat.<br />It's not a massive amount of white steam, just enough that you see it wafting up behind the boat when on the hose/tub. I almost figured it was just part of having RWC. I don't notice it when its in the water. I get no steam until after it is up to temp at 140.<br /><br />Head gasket replacement would be a severe pain on this boat.....<br /><br />I will add just for info sake, that the head gaskets are marine and the engine has never been hotter than the 185 or so it hit saturday (that I know of)....<br /><br />Edit: After thinking about it some more, I will still be checking to rule out the head gasket, but I could feel what felt like air bubbles in teh hose feeding the rear of the manifolds, which, in theory, is the first place water goes. If I remember correctly, it comes up from the drive, into the bottom chamber of the tstat housing, out to teh manifolds, back in from the manifolds, to the circulating pump and the block, the back out. Someone may need to correct me on that though.<br /><br />Edit 2: this post has a flow diagram and it looks like I am partly incorrect in my above thoughts. I still suspect something in teh tstat or pump.... Thread

 

[kwoolard]

Re: Opinion on 1976 Merc 888 cooling issue

JasonB<br />I would suggest a compression check and a leak down test on each cylinder to determine if it is a head gasket leak. <br /><br />I have the same setup 1974 888 with raw water cooling. I can run all day at idle speeds with a temp of 150 but when I stay on wide open throttle for about 10 minutes my temp climbs to 190 but stays there. After shut down, heat soak brings my temps up to 210-220 but cools right back down once started up. As for the steam, as long as it is not a huge cloud of steam, I would think it is just the cool water hit some hot spots in the exhuast system. Mine does the same thing when running on the muffs. <br /><br />I replaced my head gasket this year due to some air bubbles in my system, however, I still can feel some running through the system. I assume it just some small amount of water boiling off a hot spot in the engine. The first thing your water does is enter the block through the circulating pump. Your cooling flow network should be:<br /><br />1)In from the drive to the T-stat housing.<br />2)T-stat housing to the circulating pump then into the block.<br />3)Out of the block into the rear of the exhaust manifold.<br />4)Out of the manifold into the T-stat housing. <br />5)If thermostat is open, it goes through the risers and out the exhaust.<br />6)If thermostat is closed it goes back to the circulating pump , into the engine block to get reheated.<br /><br />Keep me posted on how you solve this thing, as I am very interested. I have done plenty of work to mine and have the temp almost to where I would like it to run.<br /><br />Good luck!

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

Thanks K, I'm really thinking my problem is in step 1 of your list. Before the replacements mentioned in my previous post, I didn't have this problem (granted, the intake manifold has been off as I tried a 4bbl upgrade as well, but it is bact to everything original at this point). I have more testing to do, but my gut is that the problem is with the initial flowsince that is where I changed something meaningful (impeller and tstat).

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

Ok, I started with the easy. I pulled the tstat and it was in properly and when I tossed it in a pan of water on the stove, it opened at almost exactly teh same time/rate as the old one I still have.<br /><br />I also pulled parious hoses and started teh engine to check flow. At idle, I was probably getting 2-3 gal/min from the drive/impeller (in a big pan, no hose pressure on the intakes). Next, pulled the hose going to the rear on one manifold. Seemed to have ok steady flow. Then pulled the front hose on the manifold. Ok steady flow there as well. Pulled a hose headed for the riser and it was about the same. I'm still not sure that there is enough water coming from the pump. When I ran it up to 1200 or so, the flow inscreased maybe 25%, not what I expected. <br /><br />By this point, the engine was too warm to try to check the plugs or compression. Next I will probably pull the LU and check the pump, intakes, and tubes. <br /><br />Verified that there is no water showing in the oil.<br /><br />The plugs are tough to get to, so I'm leaving that for last....

 

[bigbrownbuku]

Re: Opinion on 1976 Merc 888 cooling issue

an often over looked part of the water pump job is the gasket under the lower housing. if you didnt pull the lower wpump housing thats the first place to look.

 

[kwoolard]

Re: Opinion on 1976 Merc 888 cooling issue

Jason,<br />Before I changed out my beat up impeller I am pretty sure I could have filled up 2-3 gallons in a minute. Sure sounds like a flow problem to me. Try the clear hose trick from the drive to the T-stat housing and see if there are any bubbles. That would indicate if your pump job has a good seal at the base. I assume when you changed the pump you didn't have any missing/broken blades on the old impeller?<br /><br />When you go to re-inspect your pump job make you sure you don't have an obstruction in the lines leading up to the T-stat housing from the drive. Back flush everything, and while your're backflushing make sure there is no water coming from the water pocket gaskets or around the water tube grommet. If it worked fine before you changed your pump and body, I would suspect it's an installation error.

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

No broken legs on the old impeller, but will be back-flushing anyway. When I did the impeller I was in a bit of a hurry and that was a bad thing as I never got the warm-fuzzies about the way it went together. I wonder if its possible to get gust the gaskets to re-do the job as the impeller itself should be ok (unless it was bad and came apart when I ran it in the river....). Should have listened to my gut when I was putting it back together that something wasn't 100%......

 

[kwoolard]

Re: Opinion on 1976 Merc 888 cooling issue

I am sure you can, but I would just buy a rebuild kit that just includes gaskets wear plate and the impeller. Around $25 dollars for all, and you know you're going to need an impeller next year for preventive maintenance anyway. You'll probably pay more for the gaskets individually and may cost as much as a impeller kit when you done ordering. It's worth a shot though.<br /><br /> Individual Pump Kit Part Numbers

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

Actually, im thinking about just ordering a complete kit with new base and upper just to get it all. i can't remember if I replaced teh base when I put this boat together.

 

[JasonB]

Re: Opinion on 1976 Merc 888 cooling issue

Pulled the LU and water pump. No water in the LU fluid and teh impeller looks good, but there were a couple places on the gasket on top of the base that may have been leaking exhaust into the water supply. Going to order a full pump yto make sure nothing is warped.