overheating

[john hennessy]

small block ford/ mercruiser 888

due to a lack of money my cooling system is somewhat rudimentary, the water comes from the impeller in the stern drive,(new impeller kit)and runs directly to the new circulating pump, prior to this it tees off and a reduced line feeds the risers, there are no restrictors between the risers and the manifolds.

at the thermostat housing there is a very simple housing, the thermostat is a 160 degree stat, above that, the water passes to the senter riser manifolds, there is a small hole to bypass the stat, about 1/4".

test 1.
this is a reconditioned engine and i have filled the cooling system with water and sealed all the hoses, i then pressurized the system to 20 psi, there was an initial drop op 2 lbs which i atributed to the hoses swelling, it held 18psi for 5 hours.

i then pressurized each cylinder with an air line and rotated the engine by hand, holding it at tdc against the pressure, at no time did the guage on the cooling system change from the 18 psi. this convinced me that there was no leaking of combustion pressure into the cooling system and no leaking of water into the combustion chambers or cylinders.

i felt confident to put it in the lake.

test 2.
first run showed almost no reading on the temp guage, in fact i disconnected the sender and grounded the wire to test the guage which prooved o.k. i replaced the sender, no change, the exhaust manifolds were getting a little too hot to touch but the thermostat housing was slightly warm, i concluded that the thermostat was still shut due to the coolness of the housing preventing water from going to the manifolds, the risers were cool due to the raw water supplied to them.

test 3.
i removed the thermostat, the second run showed the same almost no reading on the temp guage but when i increased the revs above 3500 - 4000, the temp guage rise was immediate, at 200degrees i shut the throttle and idled the engine, there was a lot of steam comming from the thru transom exhausts acompanied by a lot of water.

within a minute, the engine temp guage was reading 150 degrees and falling, i repeated the test and the same thing occured, i returned to the dock at 4000 rpm closing the throttle at the no wake zone bouys about 30 yards from the dock, by the time i idled to the dock, it was down to just below 150 degrees.

the questions
if i drive the boat below 3000 rpm, it does not get hot enough to move the gauge above 100 degrees(the first mark on the guage)
if i take out the thermostat, allowing raw water to flow unrestricted through the engine, the engine overheats, where is all this hot water comming from?

if i install the thermostat, the engine stays so cool that the thermostat doesn't open, and the engine stays cool to the touch?

i have not fitted a clear hose from the thermostat housing to the exhaust manifolds, this will be my next test.

does the team think that air or combustion gas is accumolating behind the thermostat causing it to stay shut and due to this the guage sender is dry and won't read, as i stated earlier, there is a small bypass next to the stat

any help will be much appreciated, John.

 

[84EdH]

Re: overheating

how about a pic or three showing the hoses on the manifolds etc. it sounds like you have an old engine, with add on center rise manifolds? don't know what you mean by rudimentary system due to lack of money, but I think the raw water flow goes to the thermostat first, then water to manifolds after themostat opens.

 

[alldodge]

Re: overheating

The thermostat is needed to create back pressure to keep the block full or water, without the thermostat air can fill some voids. I would surmise that a 140 degree thermostat would be used in place of the 160.

How old are the exhaust manifolds and risers?

 

[Bondo]

Re: overheating

how about a pic or three showing the hoses on the manifolds etc. it sounds like you have an old engine, with add on center rise manifolds? don't know what you mean by rudimentary system due to lack of money, but I think the raw water flow goes to the thermostat first, then water to manifolds after themostat opens.

Ayuh,.... Sounds to me like the exhaust was changed, 'n the hose routin' wasn't,....

Merc never used center riser manifolds on a Ford,...

 

[Speakrdude]

Re: overheating

It also kind of sounds like your temperature sender is the overheat sender/switch, not the temp sender. Just a thought.
An IR Temp reader would help out here.

 

[john hennessy]

Re: overheating

o.k. let me explain the situation, i live by myself in a very small town in arizona, since the recesion the people left here in droves and here, there is no signs of a recovery, we don't even have a gas station or a grocery store any more, but i am only eight miles from the boat ramp on lake mead.

having said that, you could understand that i can't be in two places at once and there is no one to assist me when on the lake making diagnosis difficult.(can't see the engine from the drivers seat).

if i go out on the lake, i have to save up some gas for the trip, my nearest gas station is 45 miles away and any parts that i need must come ups, my nearest marine store is 65 miles away and not very helpful as they don't even keep gear oil for the outdrive.

yes this is a very old setup, the boat was built in 1973 and i have owned it since 1993,

the center risers are not original to the 888 system but are readily available for the ford 302 based engine and many are in use with no problems, there is minimal corrosion in them.

as described above is the reason for the somewhat crude cooling system, it is very basic, all the raw water goes directly to the circulating pump with a bleed off to the risers in 5/8" pipe, it leavs the engine from the thermostat housing directly to the front port on the exhaust manifolds, from there, it passes up to the risers and out.

i added the bleed to the risers because the exhaust temp was so high that it melted the hoses on the exhaust and the main engine plug harness which was touching the riser melted through the insulation.

i am a certified master tech for vehicles, with some 40 + years of experience and for the life of me cannot understand what is causing my problem, alas, i am a novice when it comes to the marine application of this engine but if the water goes in, and is clearly comming out the exhaust, then it should cool the thing down.

i am not convinced that water is comming out of the exhaust at high revs as i cannot look over the stern and see it when i am driving the boat but it does when at the dock.

could this be that when the boat is on plane with the drive all the way down, there is a restriction between the impeller pump and the internal boat hoses?

i am also not convinced of the integrity of the cylinder heads, a crack may be allowing combustion gases into the cooling system but due to the nature of the cooling system especially with no thermostat, this gas would be carried away as quickly as it could leak into the water passages unless the leak was so big but the engine runs without any missfires, has passed a compression test and 100psi of static pressure applied to the cylinders.

today, i will remove the risers from the manifolds to check for a restriction but as both sides are the same heat wise i doubt that i will find anything except broken bolts holding on the risers when i try to remove them.

keep up the good work guys and if anything comes to mind i would appreciate it, however off the wall it might be.

regards John

 

[84EdH]

Re: overheating

John, if there is a chance you can take some pics of the hose routing, thermostat area and manifolds, it will be a lot easier to get help.

Ed

 

[dpoff]

Re: overheating

I had an overheating problem on an older(like yours) 1974 engine that after many times of trouble shooting turned out to be an eroded hole on the bell housing where the water passage meets the outdrive. It was about the two oclock position where you couldn`t see it unless you were really looking for it. Baffled me for a long time till I found it.

 

[john hennessy]

Re: overheating

well i replaced the two hoses from the thermostat housing to the exhaust manifolds with clear plastic hose.

and guess what, so much bubbling that when the throttle was opened wide the water was completely displaced.

so my thinking is either a cracked head (probable), a leaking head gasket (possible but they are new and new bolts), or a cracked cylinder.

the block is full of water now, so tomorrow i will pull the plugs and see if they are wet.

 

[john hennessy]

Re: overheating

i replaced the hose from the transom to the water pump( the supply hose) with clear hose so that i could see if it was drawing in the air.

with ear phones and a hose it was drawing in air so i put it in the lake, no air in the supply hose, a small amount of air in the hoses from the thermostat to the exhaust manifolds.

ran the engine for about 20 minutes, temp guage did not go over 120 degrees even with the engine at 4000 rpm, in fact the guage started to drop.

unfortunately the plastic supply hose developed a kink which was resticting flow so i stopped the test.

when i turned it off, bubbles could be seen comming from the exhaust manifolds to the thermostat housing.

i will modify the supply hose position to prevent it kinking and try again.

i will also remove the raw water feed to the risers so that all the water passes through the engine with no thermostat at this time.

took it back to the lake, ran the motor at the dock, it appears that the hose from the transom plate to the water pump is being sucked flat,

this would indicate that the circulating pump is demanding more water than the pump in the outdrive can supply, i fitted a new pump complete and also a new hose from the stern drive to the transom and a new metal pipe in the transom, so either the pump is dead or the pipe is kinking between the drive and the transom limiting the flow of water.

but once the block filled with water NO BUBBLES yet.

time to take the lower unit off and check the pump.

 

[Bondo]

Re: overheating

Ayuh,.... John, post some pictures of the t-stat housin', the manifolds/ risers, 'n their plumbin' hoses,....

I think yer chasin' yer tail, 'n ya ain't never gonna catch it,...

The t-stat housin's used for log type manifolds, Ain't the same t-stat housin' used for center-riser manifolds,....

 

[john hennessy]

Re: overheating

well i took the lower unit off to check the condition of the impeller, it was still brand new.

while it was off, i rigged up a hose from inside the transom to push water backwards through the outdrive, turned it on and cycled the drive up, down and side to side just in case the hose in the drive was being pinched, causing a restriction in the water.

i was stumped, then i looked at the size of the raw water pump and compaired it to the size of the circulating pump, there's a clue here i thought, the circulating pump is about three times the size of the raw water pump, it's bound to pump more water than the raw water pump.

next thing that occured to me is how the mercruiser thermostat housing and the barr housing deal with this problem, the clue i was looking for was the word "circulating" in that all the water that comes in only dilutes the water already in there, a portion of the water just goes round and round, what comes out the exhaust is the same amount that the raw water pump puts in, which just supliments the hot water that is being circulated with cold water, maintaining a delecate balance somewhere around 140 degrees that the mercruiser thermostat is designed to open at.

there is a bypass in both the housings but it is minimal, just large enough to allow air in the block to be expelled on start up and just enough water to reach the manifolds to prevent them from getting too hot when the engine is first started.

if what i have described is the case then i must fit the correct type of thermostat housing instead of the "out to the manifolds only" type fitted now.

barr FM-29-0083 would suit the center riser manifolds i am using, it has a raw water input and a circulating pump output below the thermostat plus the feed from the intake manifold and two 3/4 outputs above the thermostat which will run to my manifolds. (it should be here friday)

the only other option would be to fit a much larger belt driven raw water pump that would keep up with the circulating pump.

 

[alldodge]

Re: overheating

Ayuh,.... Sounds to me like the exhaust was changed, 'n the hose routin' wasn't,....

Merc never used center riser manifolds on a Ford,...

Ayuh,.... John, post some pictures of the t-stat housin', the manifolds/ risers, 'n their plumbin' hoses,....

I think yer chasin' yer tail, 'n ya ain't never gonna catch it,...

The t-stat housin's used for log type manifolds, Ain't the same t-stat housin' used for center-riser manifolds,....

if what i have described is the case then i must fit the correct type of thermostat housing instead of the "out to the manifolds only" type fitted now.

the only other option would be to fit a much larger belt driven raw water pump that would keep up with the circulating pump.

A larger water pump is not the issue, it could help some with the heat but won't fix it.

How about some pics of what you have?

 

[john hennessy]

Re: overheating

i have managed to fit new batteries in my 15 year old digital camera so i will take some pictures tomorrow of the thermostat housing, the manifolds and the raw water supply line.

 

[john hennessy]

Re: overheating

here are some pictures

here is the themostat housing i have at present and also a shot of the end of the center rise manifold.

the raw water pump is connected directly to the inlet of the circulating pump

 

[Bondo]

Re: overheating

here are some picturesView attachment 217399View attachment 217400

here is the themostat housing i have at present and also a shot of the end of the center rise manifold.

the raw water pump is connected directly to the inlet of the circulating pump

Ayuh,.... Now We're gettin' somewhere,....

Post some more pictures further back to show All of yer plumbin',...

Part of the problem is you claimed a Mercruiser motor, which that 1 Ain't,...
Donno what it is, but my guess is that t-stat housin' ain't gonna work,...
Just the fact that the in-comin' water is plumbed directly into the circulatin' pump is Wrong too,...

 

[achris]

Re: overheating

here are some picturesView attachment 217399View attachment 217400

here is the themostat housing i have at present and also a shot of the end of the center rise manifold.

the raw water pump is connected directly to the inlet of the circulating pump

Yeah, big issue with that set-up. When the thermostat is closed, no water will be flowing through the manifolds. They will get VERY hot (boil the water out of them 'hot') and you'll have a serious fire hazard. What's more, when the thermostat does open and water rushes in to the manifolds, the sudden temperature drop will cause the manifolds to crack...

You need to set the system up the way it was originally designed for marine use. That set-up looks very 'automotive'....

Chris.......

 

[harleyman1975]

Re: overheating

There are a lot of colorful names for that but I will just go with cobbled together and leave it at that!

 

[john hennessy]

Re: overheating

1. i did not say it was a mercruiser, i said it was a 302 ford/mercruiser 888 which the drive is.

2. that is why i don't have a thermostat.

3. does anyone have a problem with the center riser manifolds?

4.yes i agree that the thermostat housing is not what i need.

5. yes i know that the raw water pump should not be feeding directly into the circulating pump.

6. and apart from telling me what i have got is rubbish, do we have any answers to what i need, bearing in mind that Bondo already stated that the original mercruiser thermostat housing will not work with center riser manifolds.

7. i have, as stated above, ordered a Barr FM-29-0083 thermostat housing and a suitable hose to run from that to the circulating pump, this will enable me to plumb the raw water pump into the thermostat housing and out to the exhausts.

8. if you were to have this boat given to you how would you replumb the cooling system using as many of the parts you already have and spending as little as possible on new parts, we could all just go out and buy a complete new motor and drive but that would not be realistic would it.

9. these were the cooling system parts i got with the boat, all i did was put them together and see if it would work, wouldn't you? as it turned out they didn't so i am only trying to change the necessary parts to have a working system.

10. next you will be telling me the 4 barrel intake and carb won't work or the electronic distributor, we won't mention the 351 comp cams cam and roller rockers or the big valve ported heads and the 10-1 pistons, this engine is designed to make peak torque at 3500 rpm and when i say peak torque i mean 400+ ft.lbs.

lake Mead is a big lake, some 60 miles long and i live at one end.

 

[john hennessy]

Re: overheating

and just for you HARLEYMAN, if i had the correct parts, they would have been fitted, likewise if someone on this site had the knowledge to know exactly what was needed in a ford cooling system and stated that, then that is what would be fitted, but all i have received is a comment like "cobbled together" or "fit the original parts" well if i knew what the original parts were that would have been helpful, now i have Bondo telling me that the original parts won't work with center riser manifolds, so you want me to buy log manifolds at nearly $800.00 by the time i ship them and that doesn't include the risers or the end plates?

not to offend anyone, but it would seem that i didn't need a seaman, a supreme mariner, a master shipwright or any kind of petty officer, what i needed was an engineer, oh, i am one, that is why i have arrived at the solution without any constructive help from this site! pitty really, and i thought this site would have been the place for information and knowledge but all i got was people telling me how wrong it was and no information on how to put it right.