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Rebuilt mercruiser 502 getting hot

G

gerald

New member
"Hiya, i been reading your for

"Hiya, i been reading your forum for quite a while and wondered if there is anyone who can suggest whats wrong here, started last year with cylinder heads corroding, so decided to rip the motor out and do a rebuild, the problem being i have to send to the good old USA for all my gear. i have a formula ls 242 with 502 cid mercruiser and bravo 1. so i have fitted new: two dart iron eagle heads, piston rings, shells, raw water impeller, circulating water pump, therm housing and therm, valves, pushrods, gaskets, bolts all being the proper marine gear, cost me a fortune but i love the boat. ran the motor up with drive in a tank, starts and runs beautiful 65 psi oil pressure every thing ok for about 20 mins then temp starts to rise oil presure starts to drop to about 30 psi, i let temp get to 220 then cut the motor, changed oil after rebuild and tried her again, same thing. took out the therm and tried her again, same thing, getting good flow out of exhausts headers warm but not hot. wondered if there could be a blockage in the engine block. what do you think ??? cheers Ged"
 
"".ran the motor up with d

"".ran the motor up with drive in a tank..."

"...ok for about 20 mins then temp starts to rise oil presure starts to drop to about 30 psi..."

Fuel leak thinning oil and dropping pressure, loose circ. pump belt, tank water temp too warm.

Drain the block and exhaust mans. and see if and what comes out?

Get a laser temp. gun to verify the temps. over the entire engine and tank water."
 
"Hi Guy,have checked oil when

"Hi Guy,have checked oil when i changed it, all ok, belt at right tension.tank temp cold with constant feed from hose, but hav,nt got a laser temp gun to check temp. think i,m going to remove exhausts on monday take out core plugs to check water ways around bores inside block to satisfy my myself.
thanks Guy"
 
Gerald:

What is confusing a

Gerald:

What is confusing about your problem is that it occurs 20 mins. later after "..getting good flow out of exhausts headers warm but not hot."

"...wondered if there could be a blockage in the engine block." You may want to look for a collapsing circ. pump hose or debris in the T'stat tower. Also verify cold water inlet from the OD at the T'stat is providing sufficient flow after the T'stat opens. That hose could also be collapsing as if there is a vacuum causing it. The whole situation sounds like cooling water is shut off to the block after 20 min. Let us know what you find.
 
"gerald;
You have a belt driv

"gerald;
You have a belt driven water pump, right
I would service it and see what happens.
What T'stat do you have in it?
Maybe change that also.

Rod"
 
"Hi all. Pulled the motor agai

"Hi all. Pulled the motor again removed core plugs, a good bit of crap and flakes off rust in the block, so poked it out, pressure washed it,blew it out with air line got it as clear as poss. fitted new core plugs checked all water ways, every thing is new except for block. refitted engine today.and it does same as before.runs really sweet 20 mins then temp starts to rise to 220f oil pressure down to 25. so i cut the motor, took out the new t,stat 160f and tried it again. just the same, running out of ideas now. HELP !!!!"
 
Ged:

Get a laser temp gun a

Ged:

Get a laser temp gun and take temps as it is running to see where the temp rises first--maybe $40 for one.
 
Hi Guy. got a mate who has one

Hi Guy. got a mate who has one so am going to borrow it.will let you know results. many thanks G.
 
"a good bit of crap and fl

"a good bit of crap and flakes off rust in the block"

You may have some closed passages in the block from that crap which may require filling the block with a powerful "HOT SOLUTION" radiator cleaner a few times and just let it sit in the sun and cook.
 
"Gerald,

Make sure your t

"Gerald,

Make sure your tank water is not geting to hot from the engine discharge. I ran my boat for ten minutes with drive in a tank and the tank water was easly over 100 degrees (F)"
 
"ged;
You are at the point wh

"ged;
You are at the point where you need to verify cooling water flow.
I would pull the water hose from the water pump at the T'stat housing and briefly run it into a bucket at 1000 RPM.
A 502 will need about 6-7 GPM cooling flow at 1000 RPM, so you should fill the bucket in 1/2 minute or less.

Rod"
 
"Hi Rod. was thinking on those

"Hi Rod. was thinking on those lines last night.will try that today.pump impeller is new, pickup holes are clear so if i,m not getting enough flow what else could it be.the water discharges out the exhausts on the swim deck so no water is returned to the tank so its always cold Todd mate. Ged"
 
"Hi Rod no i hav,nt. wanted to

"Hi Rod no i hav,nt. wanted to prove it first. it,s a bit of a job getting it in the water,distance and launch ramps etc. did,nt get chance to look at it today, tomorrow hopefully, the tank i,ve got the drive in comes just above the intake holes is that deep enough,,, Ged"
 
"ged;
I think you need to ver

"ged;
I think you need to verify your water pump flow volume, then at least you know where you stand there. Have you verified overheating with a temp gun? YOu may have a bad temp sender or gauge.

Rod"
 
"heres what i did today, was,n

"heres what i did today, was,nt sure if i was doing right by sitting drive in a small tank about 10 gallons, plus the water pressure on the mains is crap,so no good putting muffs on because she sucks the hose flat so i connected a 1 1/4 hose from raw water pump into the same small tank on the floor about 2 1/2 ft below boat started up the motor and she emptied the tank in 1 1/2 minutes.much more water going through the motor than before, so think that Rod was right not enough water flow. next step is to take it to sea i,m sure all will be o.k thanks guys. Ged"
 
"Hi folks.got boat in the wate

"Hi folks.got boat in the water today at last, started like a dream, good head of water out of exhausts,60 lb oil pressure let her get to temp then set off. everything looked fine on gauges for about 3/4 of an hour then felt a stutter from the motor backed off on throttle to tickover and oil pressure dropped to 0 alarm sounded shut the motor down, opened the engine compartment and the oil was so hot i could here it bubbling, but the water temp was ok. towed her back to base dropped the oil an hour later and it was still hot and lost all its viscosity, replaced oil and the pressure was back to normal. took her out and she did same again after 30 mins. any ideas. thanks Ged"
 
Ged;
Most big blocks have an

Ged;
Most big blocks have an inline oil cooler cooled by flow thru with the incoming cooling water from your water pump.
Is yours so equipped?
Rod
 
"Hi Rod yes its got one mate a

"Hi Rod yes its got one mate and its clean, had it to pieces, is there any way i can determine that i,m getting a flow of water through the block, its the only thing i can think it may be.its got a new circ pump. Ged"
 
"Now,!! may have found somethi

"Now,!! may have found something here but need some information. the Fel pro head gaskets supplied to me by F.B.O.systems Portland are performance marine 17048. and the installation tips say that the gaskets are ok as they are for mk 1v truck and bow tie engines, if they are to be used on mk 1v passenger and hi performance blocks they need additional coolant holes adding one at each end of the gasket which could be my problem. What i need to know is can anyone tell me which block mine is ?. engine # od616514.it is fitted with JE Pro 700 pistons, boat is a 1991 formula ls 242.thanks Ged"
 
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