88' 7.4 Mercruiser Bravo Overheating

[RepoMan207]

Vessel: 1988 Century 4500 7.4 Mercruiser with a Bravo one. Fresh water use only & 700 original hours. Bought two months ago, I have used about 70 hours with no issues other then fuel (Star Tron works mint)

As the title depicts, I am having some over heating issues on my 454.

Factors: Banged the skeg on the ramp previous trip out. First time in thousands of launchings and retrievals. No apparent damage, and it was very minimal exposer (1.5 feet if that) Took it back out a week or so later, got up on plain almost immeditly after 5 minute warm up for about 2 miles, as soon as I came off the buzzer came on. let it cool a bit (2 hours), tried to start it just to have it stall out on me. got towed back in (word of advice....get a Tow membership! It pays for itself the first time of use $217 single occurance vs. $53 for annual membership) Coincidence?...probably, but what do you all think?

Repairs thus far with out resolve: Discovered the Alternator and Sea water pump belts in the bilge rather then where they belonged. I loosened the power steering belt and checked all pulleys to discover the sea water pump to be bound up. Called the local marina to double check that it was in fact supposed to be free wheeling. I was told it was supposed to be free wheeling. To my dismay, THIS IS FALSE, my brand new pump had the same restriction. A perfectly good pump will have much resistance. I became a human pretzal & installed the brand new pump just the same, and disassembled my old one for further inspection. everything intact and looking good. Waste of $500...replaced seals and put on shelf for future replacement if needed. Replaced belts and headed for the ramp. SIDE NOTE: outlet hose is no longer avalible OEM or aftermarket part number 32 18159 & or 32 18159-1, if anyone has one or knows of one I am looking for a replacement to have on hand. Upon ramp test discovered starting / stalling issue. Very unuasual for this girl, always starts and idles likes she is brand new. Took it home and inspected plugs. Dirty and fouled. Replaced plugs, wires and cleaned carborator and arrestor & took back to the ramp the following weekend. Started right up without any throttle. Ran mint...for about 5 minutes, overheating again. Shut it down and headed home. Changed out thermostat and tested old one in boiling pot of water....worked fine, took to the ramp for another test just the same. As expected, same problem.

When I originally replaced the pump I checked for water flow with muffs by taking off the inlet supply line and letting water flow into the bilge from the transom inlet. good water flow.

I am now thinking circulating pump....but it spins freely! From what I can gather the circulating pump consists of metal fins like a auto water pump. Is this correct or is it a rubber impeller as the sea water pump? Even so, why would it free wheel if it were discombobulated...

Risers? They look almost new.

Oil Cooler? Easy enough to check....but my sea water pump impeller was intact 100%. Haven't checked yet.

No obstructions in the top ports of the T-Stat housing either.

Would exhaust flappers have any role here? Meaning back preasure....wouldn't both sides have to be substantially blocked for that to be an issue? Would this be a valid an common concern?

Other factor... Had a issue with stalling, even when it had cooled off the first go around, but especially after over heating.

Where to go from here??? Any input is much appreciated.

 

[flargin]

Re: 88' 7.4 Mercruiser Bravo Overheating

skeg/ramp --- likely not related, but depending on how hard, you may have other problems.

other part of your message is a little confusing

Have you done all of this work since the overheat? or just since the begining of your ownership (2 months and 70 hrs ago)?

It sounds like you had 70 hours of perfect time, and now complete overheat...
if so:

check ps/oil cooler intake side for blockage.

double check your water pump impeller connections, did you get them on correctly.

have you checked your oil, is it milky? Did you have any steam comming out of your exhaust?

You may want to pull the hoses to the exhaust and see if the pump is pushing water to them. there should be water in there, if they was water running on your last runs... I would expect they are bone dry and your problem is lower in the cycle.

Water coming out of the transom hose does not prove much, it is if you get a lot of water pressure coming out from the other side of the seawater pump.


good luck, Welcome to the forums.

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Flargin, Thanks for the reply.

skeg/ramp --- likely not related, but depending on how hard, you may have other problems.

Not too hard at all. I think we are good on that end.

other part of your message is a little confusing

I'm ah Mainiah....what do you want! lol

Have you done all of this work since the overheat? or just since the beginning of your ownership (2 months and 70 hrs ago)?

Yes, all work preformed since overheating. 70 great hours...till now that is.

check ps/oil cooler intake side for blockage.

I am going to check this this week when I get back up to my camp where she is parked. I am anticipating everything is ok, but it is at the top of my list.

double check your water pump impeller connections, did you get them on correctly.

I have tripled checked that at this point. I went as far as to get a mirror & magnified glass this last time to read the markings directly from the pump rather then the paperwork.....it's not in an easy location by any means.

have you checked your oil, is it milky? Did you have any steam coming out of your exhaust?

Oil, yes, everythime before turning the key. it looks brand new. As far as steam....I was in the water every time she got hot unfortunately. The damn Muffs don't like to stay where there suppose to be so I won't use them to start it (I should of bought the cheap ones)....that is unless my son wants to get wet at the time. But even then I am not crazy about him being any where near the prop; even in neutral.

You may want to pull the hoses to the exhaust and see if the pump is pushing water to them. there should be water in there, if they was water running on your last runs... I would expect they are bone dry and your problem is lower in the cycle.

I pulled these three when replacing the T-Stat and there was water present in the hoses. Should I pop them off one by one while running? I attempted pulling the exhaust tubes to check on the flappers, water flow, and blockage...unfortunetly I have never removed exhaust tubes / elbows, so I am unsure of how much force I could / should apply, and where without putting un due stress on crucial parts. They didn't want to pry away from the Y tube, elbow, or risers easily, so I re clamped and left them alone. Any tricks or insight there would be appreciated.

Water coming out of the transom hose does not prove much, it is if you get a lot of water pressure coming out from the other side of the seawater pump.

True that, I will start with the oil cooler when I get back up there. I am looking forward to it Thanks again for the reply!

 

[jaxnjil]

Re: 88' 7.4 Mercruiser Bravo Overheating

i just got a 32-18159-1 hose for my 454. not sure who your dealing with but they are still available.

you said you changed the sea water pump. these can be mounted upside down and the intake side becomes the out let. this is to allow the pump to be used on both right and left hand motors. i know you you said you checked it. a little info you might not have.

you need to take the hose coming from the oil cooler to the T-housing and make sure you have full flow there to start with.

if you have the later 88 454 there are two nylon balls in the top front hose ports on the T stat housing that have a metal rod running between them. the rod has a ball at the end of each port with a spring on each end to seat the ball in each port. you might pull the hoses off one or both and make sure any one of these arnt broken.

you need the Mercuries #9 manual for you motor. it should be in the adults only at the top of the page. it might be a 2 or 3 hour down load

you might consider changing your handle. not sure how popular repo-men are in these tough times

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

i just got a 32-18159-1 hose for my 454. not sure who your dealing with but they are still available.

Where did you get it? I have looked just about everywhere, near and far. I have been told 10 times they can get it, then after 3-4 days I get a call back saying there is none to be had and to go to a auto parts store. If you replaced yours you know full well Napa isn't going to have anything like it. The -1 series; does it just go under the belly of the oil pan like the original series or does it alter it's path to the cooler?

these can be mounted upside down and the intake side becomes the out let. this is to allow the pump to be used on both right and left hand motors.

This is exactly why I checked it three times. I was paranoid from the minute I opened the box and saw the paperwork and the two drain ports rather then one. The replacement part actually doubles as a older style clamp on bracket model as well, hence the machined nose with a 1/2" lip for the new style bolt on bracket.

you need to take the hose coming from the oil cooler to the T-housing and make sure you have full flow there to start with.

at the top of list.

if you have the later 88 454 there are two nylon balls in the top front hose ports on the T stat housing that have a metal rod running between them. the rod has a ball at the end of each port with a spring on each end to seat the ball in each port. you might pull the hoses off one or both and make sure any one of these arnt broken.

I pulled one already, but I will check the other one too.

you need the Mercuries #9 manual for you motor. it should be in the adults only at the top of the page. it might be a 2 or 3 hour down load

Thank you Jax's! That could prove to be very useful. I already have #11 for the stern drive, but I will look for 9 as well.

 

[drrm123]

Re: 88' 7.4 Mercruiser Bravo Overheating

I'd be curious why it orginally threw the belts? And work from there. Are new belts adjusted to correct tension and not slipping?

 

[jaxnjil]

Re: 88' 7.4 Mercruiser Bravo Overheating

i am swapping my alpha 1 for a braveo 3 and was able to get every part i needed to make a complete mercruiser by the book swap

ill have to look and see where the hoses came from as i used 2 different
parts sources
you need to get your PM account up and working


the hose i got came off the pump and ran under the pan then looped back up to the oil cooler. nice and tidy

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Drrm...Thanks for the reply. I to am curious about that. I am thinking of the belts failed an took both with it when it snapped.....It's the only reasoning I have been able to come with. The remaining of the three belts (power steering) seemed to be in good condition, however thats not to say it was changed out at a later time then the others by the previous owner. The sea pump belt sits in an unusual deep groove on the crank pulley making it more susceptible to wear. As far as correct tension I am concerned about the pump tension not being enough...but there simply isn't any more adjustment that can be made. There is only about an 1" - 1 1/4" adjustment that can be made on the bottom bolt on the bracket. I visually checked the pulley while ramp testing it, I am almost certain that it is turning 100%, but it is in the back of my mind.

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Jax's, Thats the baby I need. There only like $30 too. The supply line was around $100.

As far as PM's, I thought that was already set up when I signed up for the account, I will look into it right away. Thanks Again!

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Yes, I am abusing the system, I believe I need 1 more post to achieve my tenth post, thus hopefully correcting my PM problem. We will see.......

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

MOD HELP........PMing isn't permitted?!

 

[drrm123]

Re: 88' 7.4 Mercruiser Bravo Overheating

Make sure the pulleys are not rusty and wearing sides of belts, which would cause to sit deeper in pulley. And verify correct belts are on boat by part number. Good luck let us know when you find cause of trouble.

 

[jaxnjil]

Re: 88' 7.4 Mercruiser Bravo Overheating

MOD HELP........PMing isn't permitted?!

OK working now. check your pm's

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Make sure the pulleys are not rusty and wearing sides of belts, which would cause to sit deeper in pulley. And verify correct belts are on boat by part number.

Pulleys could pass for brand new condition. Belts are checked and double checked after alot of debate with the local marinas, and on line recourses.

One side note to add......I have a vacant slot on my top pulley. I have been told unanimously that it is intended.

 

[jaxnjil]

Re: 88' 7.4 Mercruiser Bravo Overheating

fyi that pully is open on mine as well. here is a pic of the belt on mine

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

hey look, it's a twin to my power plant! Thanks for the doubt cruncher. It had been nagging at my conscience ever since I noticed it.

I look at that picture and all I can think about is my neck, back, knee, shoulder & arm pains. I think my next boat is going to be based on motor placement & ease of access. The bench seat is about to meet my saws all as it is. Too bad I have new upholstery, I might actualy consider a revamping of my interior.

 

[flargin]

Re: 88' 7.4 Mercruiser Bravo Overheating

You are on the right trail.

I have an 89, and the pully setup is correct.

FYI, with your pumps, you can buy just the guts, or even the back end, A LOT less expensive. But you don't need to know that now, since you have 2

Did you ever break down your RW pump to see how it looked inside? I would make a bet your impeller has a few less fins, one got jammed, it caused the belt to spint, smoked it, and broke.


I would suggest.
1, pull PS cooler intake, look in there (another circus act) remove all the left over splines from previous impellers (use a mirror it should look like a box of straws looking down the end)
2. with your son making sure the water is on the intake, and the distributor pulled, "crank" the motor. The water should come blowing out of the exposed tube. if it stops, you have your hoses on backwards. Your picture looks correct, but I don't think that is a picture of the motor in the boat.

3. Replace the hose to the PS pump. If my bet is correct, you will have solved your problem... Let it run for a little bit, those pieces can take a while to clean out.

If it is not there, you might have bigger problems (back to the why did the belts break), so i would think it would have to have been physically in the pump. the top end should be OK, but we can look at that if this does not work.




Thermostat to Exhaust manifold lines. they get pretty stuck, first use a channel lock and see if you can 'twist 'it, sometimes it comes off pretty easiy, if not I use a hardened pick and break it clear. use a little pb blaster, a few hours before and it will come off.

Sand and paint and use a little oil as you replace them, the will come off pretty easily in the fall.

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

Did you ever break down your RW pump to see how it looked inside? I would make a bet your impeller has a few less fins, one got jammed, it caused the belt to spint, smoked it, and broke.

I did break it down, I was told when I picked up my new pump that I could rebuild them, so I tore my old one apart first when I got home to see what was needed (impeller, seals, nose cone etc.) that's when I realized I was lied to about the pulley being free wheeling. The pump was in perfect condition. No fins missing, no heat coloring on the wall, the nose cone and all was perfect. I installed the new pump just the same, and bought new seals for the old one before putting it on the shelf.

Your picture looks correct, but I don't think that is a picture of the motor in the boat.

That's Jax's Motor. I was dreaming of that being mine though (out of the belly and on a pallet, I would have this issues solved in no time if it wasn't in the belly of my boat. I have to change into a human pretzel in order to work on mine. They had to cut pieces of the back rest of the bench seat for the pulleys, and power steering pump when designing this boat. The bottom of the riser is almost level with the floor. That's how tight the quarters are. Thank god they designed removable partitions in the engine compartment to the left and right of the engine, I can atleast kneel when twisting my torso to get partially in position to change plugs and pull pumps and what not.

 

[RepoMan207]

Re: 88' 7.4 Mercruiser Bravo Overheating

So lots has transpired since last post. I have been staying at camp, but unfortunately there isn't any Internet.

I started from the beginning; first trying to find a way to tighten the belt on the raw water pump. There is a bracket that bolts to the actual pump bracket...which I had thought was stationary. Turns out it sneaks behind the harmonic balancer and connects up with the lower alternator bracket where there is a slide adjustment. Tight going, but now the belt is in correct tension.

I then tracked all water lines from the transom in. Running on muffs I had Good flow...@ Transom, pump, inward cooler, outward cooler, thermostat port....flushing hose by hose as I went. I then completely removed the thermostat housing checking for any blockage. after no results I reassembled with all new gaskets.

SIDE NOTE: Thanks Jax's, I got that NLA hose from pump to cooler!

I then removed the alternator & PS pump belts and checked for free play on the circ. pump pulley with pleasing sounds of water movement as I turned the pulley free hand back and forth.

I then moved on to outbound hoses to risers & manifolds. BINGO, I came across some blockage in the port manifold hose just below the L pipe. Rust in the form of almost sand consistency. I flushed, & vacuumed all lines. Removed petcock valves and flushed with hose directly at the tubes. The L pipe going into the port manifold was fairly clogged. I couldn't feel the back side of the inlet with my pinkie until I flushed and vacuumed. The starboard side showed no evidence of rust particles or any indication of blockage. I flushed and vacuumed vicariously just the same.

Feeling satisfied I found the problem I went to the ramp for a test.....with negative results. She overheated after about 5-8 minutes again. Once she gets up to 160 degrees it hangs in there for a minute then continues to climb steady.

I then pulled the risers, starting with the port. See pics. flushed outside of vessel, and continued deeper into the Y pipe for exhaust flapper inspection. Intact and secure. Put it all back together with a new gasket and moved onto the starboard side. All was well down to the flapper there too. there was jacket rust from what I could see in both the risers and the manifolds, but it was all solid and there was no flacking. I used a flat head screw driver to irritate the walls to be sure, still nothing.

I put it all back together and then tried a discharge test. using one water hose I flushed one hose at a time (risers & manifold, both port & starboard) timing how long it took to fill a 5 gallon pal under the out drive. 60 seconds on the risers and 62 seconds on the manifold on both sides was my findings. I then borrowed a neighbors hose and tried the same test but flushing both riser and manifold hoses at the same time. as one would suspect, exactly 30 seconds on both port & starboard. I then double checked all inlets and petcock valves, there were no new rust deposits. I suspect the risers and manifolds, although old, are still in ok condition producing sufficient water passage. If this is an incorrect statement, please speak up.

I then headed for the ramp once again.......Now I have a new problem. Upon turning the key I get a god awful grinding noise....oubviously coming from the starter. The ol?' girl always fires without a miss....ALWAYS! Now this. I am thinking I got the starter wet in all my flushing madness as there is a petcock valve just above the starter. (I not only removed the petcock, but the petcock housings when flushing, more water flow). This isn't a fast moving "shiiiiing", this is a "grrrreoout" with firing in between. I obviously put my tail between my legs and went home in utter shock and disappointment.

Has this ever happened to anyone else? Can I remove the starter and dry it out somehow, or is it cooked? I flushed 40 or so hours before ramp testing, and there isn't any signs of exterior wetness around the starter. Now I am thinking Flywheel damage :-(??? Or maybe I have had a blown head gasket all this time. But why isn't there water in the oil, or water in the spark plug holes? I have had it started and running to test the original overheating issue several times, there isn't any noise to indicate an internal problem, and other then the overheating it would be a happy engine. I am thinking I bought someone else's problems or something.

Pics to come

 

[jaxnjil]

Re: 88' 7.4 Mercruiser Bravo Overheating

RYAN; i live in a cold climate and flush my motor several times a year. i doubt you got enough water on the starter to ruin it. it might be bad or it was its time to go. are you sure the battery's are charged as you have been starting it a lot and not able to run it much? worth check as well as checking all the battery connections to the starter first.

this is just another guess but maybe you got some wiring wet and have grounded your ignition and not getting any fire to plugs so starter is not so good and not able to crank motor with no help from its self firing( hope that makes sense

did you try to run it with the thermostat out or pull the t-stat housing? and both the nylon balls and springs are ok?