1988 Mercruiser 454 overheating and under powered

[adogdrian]

Hi I'm new here, so I hope I am posting this in the right area. I bought a 1988 23' sea ray weekender with a 7.4 liter mercruiser 454. I started it up, it seemed fine until I took it out and it over heated and didn't get up to speed. I don't have much experience with inboard motors or motors in general but I have been doing research and have already checked and replaced my sea water pump ( made sure the impeller veins were going in the right direction). Made sure all the hoses are clear and oil cooler. Took the exchanger out had it acid dipped and leak tested.
That's it any advice will be appreciated.

 

[Fishermark]

Welcome aboard!

You have two problems that may or may not be releated. Overheating and failure to get up to speed.

At the top of the page there is a DIY section that has a lot of good into, including a checklist for failure to get up to speed. Look through the section for some good ino, or you can click here.

On the overheating - how do you know it overheated? Gauge? Did it feel hot? Was it smoking? Let us know what gave the indication of the overheat.

 

[Scott Danforth]

Welcome aboard, glad you joined us

incorrect timing could account for overheat and lack of performance. however each symptom needs to be troubleshot

have you tested the raw water flow to the heat exchanger?
does your heat exchanger have blocked off tubes?
have you back-flushed the raw water line?

 

[Bt Doctur]

Evidently there was no on water test ,so start with some basics. Compression test, correct spark plug firing order, throttle opening fully, timing check AND checked to see if it will advance. ,leaking head gasket ,Thermostat bad, risers/manifolds plugged up a bit.
raw water inlet /seacock partially closed.
Trying to cool a BB with a heat exchanger with an Alpha drive wont work either.

 

[adogdrian]

I did run a hose down the discharge side of the exchanger and water came out the outdrive. I also ran a hose down the intake side of the raw water pump and water came out the bottom of the boat. The exchanger was clean no blocked tubes or leaks. Haven't checked the fresh water side yet to see if its plugged in the risers, but will do that soon. And of course I forgot that the first thing I did was replace the thermostat.

 

[adogdrian]

I know it's been a while since I posted this thread but I just recently started tearing back into the boat and pulled on of my risers off. I noticed that there is a closed gasket between the exhaust manifold and the riser which are both jacketed. Is this normal? I'll try to post a picture later. Thanks

 

[Bondo]

I noticed that there is a closed gasket between the exhaust manifold and the riser which are both jacketed. Is this normal?

Ayuh,.... Welcome Aboard,.... If the gaskets there had holes in 'em, the coolant would be blown out the exhaust,.......

That is I guess the closure point in yer system,.....

The manifolds are cooled with coolant, Right,..??

 

[adogdrian]

Ayuh,.... Welcome Aboard,.... If the gaskets there had holes in 'em, the coolant would be blown out the exhaust,.......

That is I guess the closure point in yer system,.....

The manifolds are cooled with coolant, Right,..??

No idea, I guess I'll have to follow the hoses. Probably going to have to wait until Friday though. So I'll get back to you.

 

[adogdrian]

Yes manifolds are cooled with coolant, the risers are cooled with raw water.
Sorry it's been awhile I took the boat to a shop and they had it for the last 4 months. They still didn't figure out what is wrong with it but they were going to take the heads off to see if their cracked. Since I cant afford to pay them $125 an hour, so I'm going to do it. They said I had water in cylinder 5 and 7.

 

[alldodge]

Howdy and welcome back

run a hose down the discharge side of the exchanger and water came out the outdrive

If you have an impeller in the drive the water should not come out, at least not much

Yes manifolds are cooled with coolant, the risers are cooled with raw water.
Sorry it's been awhile I took the boat to a shop and they had it for the last 4 months. They still didn't figure out what is wrong with it but they were going to take the heads off to see if their cracked. Since I cant afford to pay them $125 an hour, so I'm going to do it. They said I had water in cylinder 5 and 7.

Having water in cylinders 5 and 7 generally means the head gasket. Could also mean other things but the big question. Is there any more water in those cylinders?

If water is still in there and after all this time there could be some more problems. Can you get a compression tester from an auto store on loan and do a compression test?

 

[adogdrian]

I did a compression test before I took it to the shop, they also did one. Here is the email that they sent, check attachment.

 

[alldodge]

The compression numbers look good, the number 7 might still have some water in it.

Dealer finds, exchanger and manifolds are low on water (assuming coolant), flappers are burned out, carb dripping fuel, choke is takes 15 min to open, pressure tested cooling system (assume nothing found) and they need to lake test.

If the boat is getting to much fuel it will have power issues but should be able to get up on plane. The need to lake test is the one which is a bit, you have center risers and to get water in just those two from bad flappers would get me. I would look close at the manifold or the head gasket

 

[adogdrian]

Alright thanks.I will keep this thread posted.