Need help with '89 GT 150 Johnson!

[CadillacsCowgirl]

We have a 20ft '89 Javelin 396FS with an '89 Johnson GT150 VRO engine with about 20hrs on a complete rebuild. It's 30 over and built with all OMC parts. Everything was replaced in the ignition, fuel, charge system, etc. After a bit of "tuning" she runs very strong and fast. The problem, we took it out yesterday on the St.Johns River, ran about an hour to hour and a half at varying speeds(numerous idle zones!) No trouble, as we crossed Lake Dexter the boat fell off plane, the engine clattered and sputtered, lost power and died. I attempted to re-start, it didn't want to turn over. I lifted the engine, all clear, lowered it and it fired up, but would not get back on plane. We idled towards home for about 2hrs, then, I tried once more and she jumped up on plane and, once again was cruising at an easy 55mph like nothing happened! Any ideas would be a great help. We had good water stream, I could hold my hands on the t-stat housings for a few seconds no problem, VRO was consuming oil at normal rate. It does sound a bit odd at idle speed, like a bit more engine noise. I am lost! Help!

 

[hidef]

Re: Need help with '89 GT 150 Johnson!

Start with the simple stuff check all electrical connections, compression and spark. Did you run extra oil in the fuel tank for the first 10 hours? OMC/BRP recommends 24:1 for break-in. You could have a flaky power pack follow the steps CDI troubleshooting guide for your engine to isolate any ignition issues.

 

[CadillacsCowgirl]

Re: Need help with '89 GT 150 Johnson!

Thanks for the reply, I plan to check compression and a complete visual inspection of all systems asap. We did run the extra oil for break in and kept it below 2500rpm for the first 5hrs, then below 3000 for the next 5.
Would a power pack fault cause the clattering noise when it died and it not wanting to turn over when I initially attempted to re-start?

 

[emdsapmgr]

Re: Need help with '89 GT 150 Johnson!

Have you tested to be sure the hot horn works? Possible you ran over a plastic bag in the water-stopping/limiting water flow to the powerhead. A high speed overheat can lock up an engine quickly. As well, it will be hard for the starter to restart until the pistons cool and return to normal size. You did lift the engine, possibly clearing the obstruction-always a good thing do do on an overheat. Once the bag falls off the lower unit and it is restarted, the water pump should re-cool the powerhead. As a double check, you might want to drop the lower unit and see if the impeller and plastic water pump housing show any signs of overheat. I'd recheck the compression too.

 

[CadillacsCowgirl]

Re: Need help with '89 GT 150 Johnson!

Thanks for the reply, I'm planning a compression check tomorrow first, then already broke out the factory service manual to test temp sensors, warning horn, and t-stats. I'm really swaying towards an overheat. We're just praying we didn't cook a brand new rebuilt but, after a couple hours of idling toward the dock she did jump right up on plane and make the last few miles home as strong as new with no incident whatsoever... Fingers Crossed!

 

[CadillacsCowgirl]

Re: Need help with '89 GT 150 Johnson!

Pulled the t-stats out this morning and found a bit of sand in the left side, both t-stats are new from the rebuild. While inspecting I noticed that the plunger on the clean side turned freely and would rattle when i shook it, the other didn't. I turned it until it was free and then tested them by slowly heating them in a pot of water on the stove, the stiff one opened slower and not as far. I believe I found the initial cause of our issue. Any input would be appreciated...

 

[CadillacsCowgirl]

Re: Need help with '89 GT 150 Johnson!

Did a compression test... 120 across the board (whew). Replaced bad warning horn and now on to a little thermostat "modification". Fingers still crossed!

 

[emdsapmgr]

Re: Need help with '89 GT 150 Johnson!

Keep in mind that once you are on plane, that the pressure relief valves open in each thermostat housing. When these open, they permit that side of the block to flooded with a significant amount of extra cooling water. Even with bad stats, it's unlikely that you'd incur an overheat when planing. On the other hand, once you fall off plane, these pressure relief valves close and the engine is now dependent upon any water coming through the thermostats. Sounds like your stats are not working normally. Am very suprised that you'd have thermostat issues considering the powerhead is recently rebuilt-usually they are a normal replacement item during any rebuild.

 

[CadillacsCowgirl]

Re: Need help with '89 GT 150 Johnson!

Thanks for the input. We were surprised as well but the left side t-stat was actually bound up by a bit of debris. On the advice of multiple outboard mechanics in our area we performed a modification on our t-stats, flushed the cooling system, double checked the gap on the plugs, reassembled everything, test ran her, no issues so we headed to the St.Johns River. She performed perfectly. I believe we were very lucky. Thank you to everyone who provided input!