502 Overheating --- help
 

1992 Mercruiser 502 carb ( 390 hp) ----

On the first day out this season my 502 started missing. After evaluation it had a blown head gasket between #1 and #3. I could not figure out why.

I pulled the heads and had them fully reworked, including milling. I installed the heads using Fel-Pro Marine gaskets.
I installed a new sea pump impeller. The engine has a cross-over.
The engine started up great and I tuned it on the hose. Initial timing at 14 degrees with Thunderbolt IV ignition, 34 total.

During lake test, it could barely plane and will only pull 4200 rpm max. The engine temp rises pretty quickly and gets hot. The water coming into the sea pump is cool and the hoses are cool going through the oil cooler and into the engine. The water coming out of thermostat is scalding hot (I removed the t-stat). There is sufficient water flow out of the exhaust and it is steamy as it comes out. It is getting plenty hot. There is no water in oil.

I am puzzled and looking for advice.

Could the head gaskets be wrong ? This is my first guess. I do not know the number ( I have the box at home ).

Cracked block ?

I still do not know what caused the blown head gasket to start with. I am thinking this is all related, obviously.

Looking for advice. Thanks in advance.

you didn't get the hoses on the sea water pump backwards, did you ? or stuff a rag in them when you had them off and forgot it ? ( assuming all else like firing order and all the easy stuff is correct)

No, it seems to have good water flow. Water is definitely coming out of the exhaust in what seems like a normal flow rate.

correct me if i'm wrong but didn't that tstat housing have a little l shaped by pass hose ? and if so then the tstat didn't have a bleeder but on the ones where that bypass is blocked the tstat has a little tiny bleeder hole/bead looking thing... you maybe get the wrong tstat ?

oh... and does that ignition need the jumper to set the ignition base timing ? and are you certain you got that right ? like maybe you used one of those lites with the dial it in advances and somehow doubled what you put in ? it sound like you are way down on power as well...

I would pull the hoses off the risers, start the engine and see if you have compression coming out the water jacket circuit (hose from engine). That will tell if you have a crack somewhere or another blown head gasket. This assumes your engine is sea water cooled. Also I presume you checked the deck for a low spot?

I pulled the t-stat out.


I thought TB IV does not need to be jumped. ?

I am about to go back to the dock and I will check that. I did check deck best I could with straight-edge. Everything looked fine.

No jumper needed on tb IV. But I've made that timing light mistake before that stevexm mentions with the advance setting.

I have Gen V block and the Fel-Pro box said head set was for Gen V 502, so ...

I will get part number tonight.


I keep thinking head gaskets could be wrong .............. ?

this is a long shot but i got my boat originally because the prev owner blew up every 454 that he could buy and finally there wern't any more. . the starboard ones all blew up because he had the oil lines backward and the port ones blew up because the seawater inlet hose got soft ( no wire reinforcement ) and would suck itself closed and roast the motors. you don't have something crazy like that going on, do you ?

Fel Pro # should be 17048.
Eddie

What water temp are you seeing on the gauge? You shouldn't see more than 120 without a t-stat.

The gauge seems to be stuck, or is stopping at 145*. I am sure it is faulty. It was working fine before.

I worked on it last night ----

The water pressure is stronger coming out of the right exhaust pipe. There is water coming out of left exhaust, but it is somewhat weak. Probably 50% less than right side. The previous head gasket problem was on left bank. ( ? )

Also- I pulled the hoses off from manifold to riser ( Stainless Marine Hi-Torque manifolds ). The water pressure / flow seems very good going into the riser. The strange thing is, there is exhaust pressure coming back out of the coolant nipple on the riser while engine is running. Is this normal ? The water is not introduced into the exhaust stream until the end of tailpipe.

Thoughts ?

It could be possible if you have something providing backpressure to the exhaust gas after the point where the water and exhaust gas meet (flappers). I'd check the other side to ensure it is the same. What will tell the tale is what comes out the hose that is leaving the engine to the manifold.

I do have exhaust flappers (internal) inside the exhaust tip as well as external flappers on the outside of tip.

The water coming out of the engine going into the exh manifold is HOT.

Does compression gas come out the hose from the engine when you start it with the hose disconnected from the manifold? You might want to hook up a second water supply hose to the manifold so you can run the engine with that hose disconnected from the engine to manifold without fear of overheating the exhaust manifold. If the disonnected hose has compression it will look just like you are looking at your tailpipe when running with water/compression exhaust mixed. If there is no compression gas you will just note the water flow pulses from the seapump impeller with no exhaust.

Does not have exhaust compression from this hose. The water flows freely with "pulses"

I used a Felpro Marine head gasket set #17249.

On the box it says this is for Gen V 502 / 540 / 572


???

My block is a "Bowtie" 502.

You should be able to rule out cracked head/block then so that is good. I believe I would do a compression test on 1 and 3 to make sure there isn't another issue there.

Fixx
 

From what i remember the bowtie blocks were not gen V they were mark blocks..

what year is your boat or engine.. if its a bowtie block it would have the chevy emblun caster on the side of it..

the 17249 is a upper end gasket kit for a gen v engine..

Do you remember if the lower water jackets in the heads were a diamond shape ?

The boat and engine are 1991. Yes, there is a "bowtie" cast into the side of the block.
I am a dumbass and cannot remember if the holes were round or diamond shaped.
The label on the box said it worked for "502 Bowtie".

I am now confused ..................

Fixx
 

just remove the valve cover and look for a casting number,i think the last 3 are 088 for gen v heads..or pull the casting number off the back of the block and check that one,,hate to say it but i think you used a gen v head gaskets instead of the mark VI gaskets..

read this,,it reads yes and no on the gaskets you used???

http://www.marinemechanic.com/site/page173.html
Save yourself the felpro headaches,,call bob at performance gaskets,he will steer uoi in the rite direction and will get you the rite gaskets..262-677-4830..way cheaper too.

[QUOTE=mrfixxall;3464939] i think you used a gen v head gaskets instead of the mark VI gaskets..


You mean Mark IV gaskets right?

I have 088 heads.


I may be wrong but I thought there is no such thing as a Mark IV 502. ?

Fixx
 

yes but you mentioned bowtie which is a 10.200 tall deck which made me believe you had this..scroll down to P/N 12370834


http://www.crateenginesonly.com/Chev...tie4250td.html

check the casting number on the back of the block and find out forsure what you have..

check the side of the block by the motor mounts,,if theirs a 8.2 then its just a standard 502 gen V block..

I checked the block casting #

10051107

...which is a Mark IV 454 Bowtie block :lolhit:

So ------ there`s my problem.

It`s a siamese-cylinder 4.25 bore block that is bored to 4.50".

Fixx
 

you mean 4.470 lol 4.50 would make it a 509 :lolhit:

call that number i gave you (post 24),,save the scratch,bob is a great guy to deal with..

I called that number several times today. I kept getting a fax machine ( I love that sound....)