Mercruiser 888 overheating

[Deepwtr]

I have a Mercruiser 888 (Ford 302) with cooling problems. The first day I took it out the engine didn't get up to any temperature but the manifolds got real hot. So the next day I do some investigating and found that there should be a separation plate between the elbows and the manifolds. So I got the block off plates and installed them. Now the motor gets REAL hot and the manifolds are also still hot. So here is what I did to troubleshoot:<br /><br />First, unhooked the line coming from the stern drive pump and ran it a little bit with the water muffs. Flow was great. Took off the inlet and outlet lines to the manifolds and ran water through them. Flow was great. Ran water through the exhaust elbow. Flow also seemed to be great there. <br /><br />I have replaced the engine water pump and the thermostat, and I have not noticed any water in the oil. At this point I am at a complete loss as to what it could be? <br /><br />It seems to be running great, is there any what that the timing could be off far enough for it to overheat and yet still run good? <br /><br />I will take any suggestions at this point! Thanks.

 

[Reel Poor]

Re: Mercruiser 888 overheating

Is it raw water cooled or does it have a closed cooling system?

 

[Haut Medoc]

Re: Mercruiser 888 overheating

I have an 888 with closed cooling, if you have raw water cooling, you don't need restrictor plates. Post back the answer to Reel Poor's question. I don't think it's a timing issue.

 

[Deepwtr]

Re: Mercruiser 888 overheating

Sorry, it is raw water cooled. Outdrive pump runs it into the thermostat block and from there it gets sent on its way. <br /><br />Originally without the plates the motor didn't hardly get up to 140, but the manifolds got (at least what I thought) fairly warm. How hot should they get? According to the manual even with raw water cooling I need the seperation plate. Is that not right?

 

[Haut Medoc]

Re: Mercruiser 888 overheating

The manifolds will get warm/hot, you should be able to touch them briefly without getting scorched though,[cooler than auto], and at the top of riser as well. If it runs 140 @ the thermostat, without the plates in, I would leave them out. Do these plates have any holes at all? What manual says you need them?

 

[Deepwtr]

Re: Mercruiser 888 overheating

Well, there is a picture of them in the Clymer manual for the open loop cooling. Water gets sent in the back of the manifold, without the riser plates what causes the water to get pushed through the manifolds instead of up and out the elbows?

 

[Deepwtr]

Re: Mercruiser 888 overheating

The plates have one small weep hole in the front.

 

[Haut Medoc]

Re: Mercruiser 888 overheating

I don't have the manual in front of me to see your exact set-up. On a closed system, the water comes from the drive to the heat exchanger to the"T" then to the risers and out. Does yours not feed directly to the engine water pump from the drive? I would think that without the plates the engine water pump would push the water out of the risers.....and I will say this........both Clymer's and Seloc are notorious for mis-information.

 

[Deepwtr]

Re: Mercruiser 888 overheating

The drive pump feed the thermostat block on the front of the engine. From there water gets distributed out between the motor and manifolds. The engine water pump pulls water from the thermostat block.

 

[yoced]

Re: Mercruiser 888 overheating

His set up is correct, as long as he has the hoses correct on his thermostat.<br /><br />see this post here for diagram of thermostat hookup: <br /> previous post on three hose 888

 

[Deepwtr]

Re: Mercruiser 888 overheating

The hoses are correct on the thermostat. I have gone over them about 100 times. Yes, I was really that stumped. So is it correct that I don't need the plates between the manifold and the elbows?

 

[yoced]

Re: Mercruiser 888 overheating

No, you do.<br />It was not a wonderful set up from the guys in oklahoma, but it was how it was designed and you should be able to run in the correct temp range when it is working properly.

 

[Deepwtr]

Re: Mercruiser 888 overheating

Ok, so I'm out of thoughts. Can I just re-run the drive pump into the back of the manifolds and then run the front of the manifolds into the circ pump and then out the elbow risers? That would be very similar to the way a jet boat is setup. I am running out of options and ideas.

 

[Deepwtr]

Re: Mercruiser 888 overheating

Also, is there another type of block off plate that might have bigger holes than the ones I have with the weep holes?

 

[JasonB]

Re: Mercruiser 888 overheating

I'm thinking my block-off plates have slots, but I can't remember as it's been 3 years since I had it apart. My 888 is RWC as well.

 

[Deepwtr]

Re: Mercruiser 888 overheating

Well, tonight I ended up taking out the thermostat and everything ran great. The manifolds ran right about 120-130 and the motor was 115. I haven't had a chance to check out the thermostat to see if it was actually opening like it is supposed to, however what if the thermostat is opening like it is supposed to?

 

[Haut Medoc]

Re: Mercruiser 888 overheating

Is it possible that the t-stat was installed backwards? 115 is too cold, running that cold can't be good in the long run. Has the t-stat been replaced? With a good one it should keep it warmer. The manual does say that you do need the restictor plates by the way............

 

[JasonB]

Re: Mercruiser 888 overheating

The motor should run 140. Mine never gets over 160 or so.

 

[Deepwtr]

Re: Mercruiser 888 overheating

The thermostat was put in with the element and spring facing down into the thermostat housing.

 

[Deepwtr]

Re: Mercruiser 888 overheating

The thermostat opens right at 140 degrees like it is supposed to. So what now?