Possible head gaskets installed improperly?

[JS99Z]

Hello, I’m new to this forum. I have a 1989 Four Winn’s Horizon with a 4.3l OMC cobra.

I recently had the engine rebuilt. It starts up fine and runs fine, but when I check the heads with my infrared thermometer they measure way hotter than the block and intake. On the first trip out on the lake the heads got up to 240 and I shut it down in fear of blowing a head gasket or cracking a head. The big hose going to the circulating gets pretty hot, and the engine will make gurgling or boiling water sounds also when the heads get that hot.

The block runs around 160 on the gauge and with my thermometer.

I have changed the impeller, the impeller housing gasket, circulating pump on the block is new, thermostat, and o-ring are new. The exhaust manifolds are brand new so no clogging there.

I have water flowing up from the outdrive to the thermostat housing, and water exiting out the transom.

I’ve done a leak down test. Checked out ok. I did it with thermostat housing off and didn’t get any bubbles.

I am am kind of at a loss, and I don’t know what else to check. The engine builder is not being any help and kind of blowing me off. Is it possible he installed something wrong like head gaskets or intake gaskets that are causing my problem?

Anyone else ever have this issue and how did you solve it?

Thanks in advance!

 

[Lou C]

I don't think you can really install the head gaskets on a 4.3 wrong, same for the intake gaskets. If the heads are getting that hot it suggests that water is not flowing out of the top end of the engine, perhaps due to flow problems in the thermostat housing.

On a raw water cooled engine when its cold, the stat is closed and water in the block and heads just recirculates, via the big hose. The water from the impeller exits from the stat housing to the exhaust system. When the stat opens, hot water from the block, heads and intake manifold exits via the fittings on the stat housing that feed the exhaust system, and cool water from the impeller gets sucked in to cool the engine.

You said the exhaust manifolds are new....the original one piece manifolds used on the 4.3s have not been available for many years. Just what exhaust do you have on there? And if you have the one piece units, are the exit ports open? They are small and clog up easily. Make sure all the ports in the stat housing are open and not necked down. Make sure those 4 exit ports on the one piece exhaust units are open. I upgraded mine to the center riser exhaust the later models used. Their exit ports are much bigger. For the engine to stay cool you need a steady flow of cool water in, via the impeller, and out via the exhaust system. I'm surprised your dash gauge does not indicate overheating. The water flowing out of the heads, flows up into the intake manifold (that's where the temp sending unit is). So if they were getting that hot, the water exiting them should be hot too and that should show up on the gauge.

 

[Lou C]

Original block and reman heads....this was before I cleaned out some of the smaller passages in the block you can see some were rust clogged.

 

[Scott Danforth]

are you measuring the heads, or the exhaust manifolds?

anything over 200 is hot on anything

your block and heads should be about 160
your exhaust manifolds and risers should be about 180

with the one exception is the exhaust manifold flanges will get a little warmer right where they meet the head.

 

[JS99Z]

The exhaust manifolds are a 2 piece manifold/risers from Barr/Osco for new Omc’s probably the same as yours.

The temp sending unit is brand new and the gauge is registering almost the same as my IR temp gun.

The hoses going from the thermostat housing to the exhaust manifolds are ice cold during the whole run time, until I shut the motor off. Then they get warm instantly. The water from the transom is probably lukewarm.

How big should the openings in the t-stat housing be going out to the exhaust manifolds? They look corroded somewhat. (It is a freshwater boat by the way.). I could try to open them up some. Is there a passage inside the thermostat housing that I can’t see that maybe restricted? Also the new hoses going from the thermostat housing to the exhaust manifolds are not as stiff as the originals (originals ended up being short). Could those cause restriction?

Sorry for all the long questions. Just want to get this figured out before I have to winterize.

Thanks

 

[JS99Z]

I’m measuring the block at 160, the intake measures around the same. The heads will climb in to the 200’s and higher if I let them.

 

[Lou C]

The way the cooling system works, the hoses feeding the exhaust manifolds will be cold till the stat opens, then they should get warm (when your dash gauge reads 160*) as it opens and lets the hot water to exit via the exhaust system. There is a bypass port in the stat housing that can get clogged by old impeller bits. I'd take off the stat housing and test the stat in a pot of boiling water. Make sure it opens at approx. 160* and opens all the way. Then ream out all the passages in the stat housing with a coa hanger wire or similar. I replace these housings every 5-7 years in salt water just like exhaust elbows due to rust. It sounds like your exhaust is not the problem, do you have the exhaust flappers installed at the top of the Y pipe? If they melt due to an overheat they can fall down and block the exhaust.

As Scott asked where are you checking your cyl head temps? On the water hose, mine are about 150 at most unless you measure at the exhaust port. The exhaust manifolds and elbows are less than 100*, the only part higher than that is the starboard side 90* exhaust pipe will hit 140* at the hottest, the other side is about 100-110*.

The gurgling noises does suggest the water is too hot in the cyl heads. When it was rebuilt did they change the heads? If so what heads were used? Were the heads checked for cracks? Cooling passages clogged? The Fel Pro head gaskets I installed can be installed either way there is no way you can install them wrong.

Again with the problem you are reporting, it does not make sense that the water in the cyl heads is boiling and the temp gauge reads normal.

 

[JS99Z]

The heads are original but where cleaned up and milled. They were supposed to be checked for cracks according to my paperwork from the engine builder.

When I measure the head temp I am measuring the front each head like where the accessory’s would bolt on if it was in a car/ truck.

Exhaust flappers are still intact and still functional.

I have bought 2 new thermostats and the same result.
How far should the thermostat be opening in the boiling water? I’ll try again with a more accurate thermometer with the boiling water.

I will also try to clean up the t-stat housing and check for any obstructions. Are new housings available?

 

[Lou C]

According to my factory shop manual the stat should start to open between 157-163* and open to 5/32nds min at 182*. If the housing is NLA from OMC, they can be bought from Volvo Penta because they used the same housings. Same part # too.

https://www.crowleymarine.com/johnso...cfm?mdl=ZFVP8M

crazy expensive, I paid $60 for the first one I bought and about $80 for the second one I bought.

http://www.volvopentastore.com/Cooli...view_id.775986

cheaper here part # 3850360 same part $147.

take a look at yours first before replacing, in fresh water I doubt they go bad unless your water is pretty corrosive.

 

[Howard Sterndrive]

are there different riser gaskets for those osco's for closed or open cooling? or some nonsense like that maybe?

 

[Lou C]

here's a pic of the thermostat flow with a closed and open stat for the OMC/Volvo style stat housing....

 

[JS99Z]

Last night I took the thermostat housing off, and pulled the t-stat. I ran a wire brush, coat hanger, and compressed air and didn't find any blockages. Out of curiosity I ran it without the t-stat, with the same results. Only it seemed like the heads got hotter quicker. Tonight I will retest both of my t-stats that I have in boiling water.

I did find out the gasket kit that was used. It was part of an engine rebuild kit by Engine Tech MKM262AP. The website says it is for marine application.

Is it possible I have air in the system? Or I am sucking air from somewhere causing the heads to get hot and the gurgling?

 

[Howard Sterndrive]

I'd try clear hoses between the tstat hsg and the manifolds - watch to see if water can exit through those oscos. maybe try a clear hose from sterndrive to housing too to see if impeller delivering good, air free water.

my guess is water can't get out

 

[Lou C]

before the rebuild...did this engine have that problem...I've run one of these in salt water for years...and have had some overheating issues but they were due to things like marine growth clogging the water intakes on the drive...I never had an issue where only the cyl heads were getting too hot. It has always run at approx. 160 and at most will rise up to 175 after coming off plane.

 

[JS99Z]

The original motor almost went 30 years. Overheated it once due to a cracked impeller housing. Was fine before that and fine after that. Never any gurgling or boiling sounds. Never checked the temp on the heads on the original either.

What sizes are the hoses from the t-stat housing to the exhaust manifolds, and the hose from the stern drive to the t-stat housing? I wanna try the clear hoses.

thanks

 

[Lou C]

The hoses from the stat housing to the manifolds are 3/4” or 19mm. The one from the impeller is bigger, 1” or 1 1/4” I forget...measure it to make sure.

 

[JS99Z]

Would it by a bad idea to take the impeller housing off and run a garden hose directly to the t-stat housing just to try to eliminate the engine or the outdrive as the issue? Does the outdrive need the water for cooling? Just an idea let me know what u guys think. Thanks!

 

[Howard Sterndrive]

Would it by a bad idea to take the impeller housing off and run a garden hose directly to the t-stat housing just to try to eliminate the engine or the outdrive as the issue? Does the outdrive need the water for cooling? Just an idea let me know what u guys think. Thanks!

you can tee into that hose with an automotive rad flushing tee. That way water will flow back to lube the impeller too.

 

[Howard Sterndrive]

garden hose on full blast

(and anytime you loosen that cap in the lake at idle, you'll know your impeller is healthy as it sprays water out)

 

[Lou C]

That will work for sure but even if you remove the impeller housing and feed it from the thermostat housing, the exhaust waer flowing through the Y pipe should cool the drive adequately, just for a quick test. That is an odd problem, it almost seems like some debris from machining etc is blocking water flow out of the cyl heads. But if that were the case...then the intake manifold water heated area should be just as hot and the temp gauge should register overheating.