GT150 Overheating long term issues

Hi

I have a 1989 150 GT V6 that I recently acquired on the back of a Four Winns 180 Horizon

In general it runs pretty well for a 27 year old engine and I am in the process of slowly repairing/replacing any old or obviously worn parts. Yesterday I thought I would clean and inspect the ignition system and took off the coils and HT leads.

I can now see evidence of what I assume is overheating as some of the coils on the right hand bank (as you look at it from the rear) are 'melted' where they are bolted to the head, the primary wire shrouds are melted in some places and the black paint on the head shows signs of blistering.

I have recently replaced the pressure relief valves as the white plastic inner valves were deformed which I now suspect was caused by the overheating. Also the temperature sensor switch on this bank is deformed (new one ordered).

My question is - what else could have been effected by this overheating that I should be sorting/worried about?

I have checked the compression levels and have readings of 65-75 psi that I hope are low because of my cheap gauge (new better one ordered).

Any help or advice gratefully received.

Phil

My question is - what else could have been effected by this overheating that I should be sorting/worried about?

Click to expand...

Well could have scuffed pistons,rectifier/regulator damaged,base gasket damage also the 86-89 madel are known for spark plug wires burning out(TSB issued)...

Any time there is an overheating problem I always look at the water pump

Ok thanks guys.

She pushes the Horizon 180 up to about 35mph with a WOT of about 5k using a 14.5 X 21 prop with 2 on board.

Does this sound about right?

The boat is rated to a max of 150hp so can't go any bigger and I know the boat is guide heavy but was hoping for a bit more top end speed and am worried it's because of some underlying damage from the overheating.

it would be nice to get the engine Dyno tested to see what it's actually producing after 26 years.

Tick over isn't great after a hot run and just feels a bit lumpy sometimes. I am running Redex fuel additive through it at the moment to see if it clears any carbon build up.

Cheers

Weight of boat,size of fuel tank,type of hull,load on board all come into play. Is cavitation plate level with keel of hull? A prop with less pitch,say 19" will give you theoretically 400 more RPMS. What's your wot range?

More RPMS will not necessarily give you more top end speed and may change hole shot& planning speed/rpm!

Overheating to the degree you speak of can loosed the head bolts and damage the head gasket which would affect compression and eventually allow a water spray to enter the combustion chamber (not good!).

Double check the compression..... With "all" spark plugs removed, the compression on that engine should be approximately 95 psi on the starboard bank and 90 psi on the port bank.

Check the head bolts for looseness and torque them to 18-20 foot pounds in the following sequence whereas each number is a head bolt:

17....18
13....14
9.....10
5......6
1......2
4......3
8......7
12....11
16....15

Thanks for all the feedback and advice - much appreciated.

Checked the compression today and am getting 85-90 psi across the 6 so this is probably as much as I can hope for on an engine, this age.

I want to take off both heads and check the bores and piston crowns as I suspect these may have excessive carbon build up but need to sort two new gaskets first as I assume these will be trashed when I take them off and a good idea to replace anyway.

Im also going to try a 15 X 23 prop to see if this makes a difference and see how it performs.

Will also remove all carbs and give them a deep clean and sort a water pump repair kit.

Cheers

While you have the cylinder heads off, check the water deflectors............

(Water Deflectors)
(J. Reeves)

Water deflectors are actually lengths of 3/8" outside diameter rubber hose, installed between the top cylinder and any cylinder beneath it, and also between the bottom cylinder and the block. The purpose of the deflectors is to have the water follow a definite path around the cylinder walls. Unfortunately the deflectors between the cylinders will at times swell sideways due to either a previous bad overheating problem, or simply due to age and salt corrosion. This causes a water flow restriction which usually allows the water to cool sufficiently at low rpms but not at the higher rpms.

This hose material can be purchased reasonably at any automotive parts type store if you care to make your own, or you can purchase individual deflectors at any Evinrude/Johnson dealership at a somewhat higher cost.


Removing and installing them can be a hassle at times, but not always. I use a sharply pointed scribe with about 1/4" of the tip bent at a right angle whereas I can reach in, jab the tip sideways into the rubber, then yank it out. It's necessary to clean the seating surfaces where the rubber contacts the block with a small rat tail file to eliminate salt deposits etc. When installing the new rubber deflector, coat the deflector and the metal surfaces with WD40 which will act as lubrication to allow it to go in as easily as possible.


Make sure that you insert something into that deflector area before cutting and installing the deflectors if you make your own so that you will be certain that they are the right length and also that they will be seated properly. Usually a very small amount will be left extending above the block sealing area..... simply cut the excess off with a single edge razor blade.

Before removing heads,Iwould decarbonize engine using OMC engine tuner,and see where that goes,follow instructions on can carefully,compression usually increases, More than one application may be necessary ! Head gaskets are not reuseable, Use omc sealant on new gaskets. HEAD preparation is crucial prior to reinstallment of heads,Check heads for warpage,If ok,place heads on a perfectly flat surface,ie plate glass,plate steel,Sand in a figure 8 pattern over 220-320 wet/dry sandpaper until uniform color & texture is reached. thin film of omc gasket sealer is recommended on both sides of gasket!

Thanks Joe - will do.

Thanks johnnygjr - will do.

Just one more thing Joe...

Do you know what kind of temperature range this engine should run at?

I have a temp gun so could use that

1989GT150V6 said:

Just one more thing Joe... Do you know what kind of temperature range this engine should run at? I have a temp gun so could use that

Click to expand...

There's a thermostat and water bypass valve assembly at the top portion of each cylinder head. The thermostats normally open at about 143 degrees so the engine will be running just slightly higher than that but not excessively.

Pertaining to gasket sealers... see below:

********************
(Gasket Sealers)
(Usually available at any reliable automotive parts type store)
(J. Reeves)


Do Not use any type of sealer on outboard carburetor or intake manifold gaskets as this would cause blockage of various fuel/air passageways. Also, there are new type gaskets, including head gaskets, which are used through out the engines that are coated with a substance that gives a shinny appearance to them. These gaskets are coated with a self sealer and are to be installed as is.... no sealers! Older style head and fuel related gaskets that are not coated with this substance are to be simply coated with oil.... nothing else.

All other gaskets (hopefully I've not overlooked anything above) should be coated with Gasket Sealer (the type that comes in a can that has a small brush in its screw off cap). This also pertains to some water pump installations that use a gasket between the plate and the lower unit housing.

Marprox Sealer 1000 or OMC Adhesive or Boat Armor Sealer 1000 (same substance)[See Below Note] should be used on any metal to metal (Unless GelSeal Is Called For) or metal to plastic surface (such as impeller hsg to plate, and plate to lower unit surface) to eliminate air leaks. It should also be used on the Spaghetti tubing that is used on many powerhead crankcase halves, lower unit skegs, etc. I have found that this substance works quite well on various "O" Rings such as what are found on lower unit carrier and upper driveshaft bearing housings (Note that this substance is obviously not to be used on all "O" Rings). This substance also works quite well in sealing the surfaces between the lower unit and the exhaust housing to which it attaches, eliminating the unsightly water spray between the two after completing a water pump installation.

NOTE 1: Marprox Sealer 1000 and Boat Armor Sealer 1000 is no longer available.

NOTE 2: OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964

DO NOT use any sealer on the large "O" Rings that are used on the upper and lower crankcase heads (The housing/heads that slide over the top and bottom of the crankshaft). On those "O" Rings, use only a coating of grease.

The exception of surface to surface contacts pertains to the later model matching crankcase (block) halves (which does not incorporate spaghetti tubing) which call for "Gel-Seal", or any other surface that calls for Gel-Seal. This substance seals in the absence of air, and if called for, must be used. One other form of Gel Seal that can be substituted is "Loctite #518". Nothing else that I know of will do!


I advise against using silicone or permatex on a outboard engine. It simply will not function properly. The exception to this (as per OMC's recommendation), is to use the black Permatex (heavily) on the gasket 306242 which seperates the inner exhaust tube from the exhaust housing on the 1959 35hp and 1960 to 1970 40hp OMC outboards.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
********************

Ok thanks Joe.