Overheating 350 in 1977 scarab 300
 

I have a 1977 Scarab 300 with factory twin 350's and TRS drives. Starboard motor is running hot, pulled seawater pump no damage went ahead and put new impeller in and new thermostat and motor is still running hot (no noticeable steam out the back and no water in oil), seems to have plenty of water coming out the back. Temp on exhaust is about 200 on both sides and risers are about 90 to 100 or so. Port motor is about 100 on exhaust and risers about 90 or so. I pulled exhaust and everything is clean and no scaling at all. I am struggling with this and could use any advice on this. I am new to the TRS drives and have not checked the flapper or anything waiting on manual in the mail. The exhaust to riser gasket has the water jackets blocked off on both sides of the exhaust. Boat came from the Ozarks and was in a barn in Conroe for 10 years or so and previous owner pulled heads and had them reworked because both cams were flat from original owner not setting valves correctly. So new cams, heads reworked, new intake and 4brl carbs transmission cooler is routed out the back and not thru exhaust anymore and has great flow. Sorry for all the info but more is better.

Its reading and is hot in the thermostat housing ,both manifolds on that motor are too hot to keep a hand on ,but the risers are normal temp? Are those the old brick style rear exit? Amazing there not clogged.
Does it get hot idling at the dock and just get hotter when moving the boat under a load? Do you have enough room in there to have your pump draw water out of a bucket or pan on the trailer to check the flow? How about flipping your inner 2 exhaust water dump hoses port to starboard and monitor those manifold temps,
Grab a water pressure gauge and use that ,to find restrictions , sounds like you have already ruled out a trans issue spiking your inlet raw water temps

Post a pic of your exhaust manifolds and your thermostat housing. If you can also post a pic of those gaskets.

Chris

What are the water temp guages reading???????????

Are you running on a hose or in the water????

check balls stuck if applicable in t stat housing or water circ pump. Also are all water jackets completely non restricted in the exhaust system. Wrong riser gaskets ?

problem started in water and now troubleshooting off the hose, lake is not real convenient to run this boat in (Lake Houston) its normally on Conroe but will be on Rayburn after this fix. I can probably pull out of bucket with raw water pump I will try that. The Temp rises faster under a load and take a long time to cool down idling but is still hot, running at dock or off a hose temp comes up pretty fast. The temps I posted were after running off a hose at idle for 15 min. I brought a Bore scope home and plan on looking in manifolds and looking to see If flapper is where it needs to be, I don't have thru hull exhaust so all exhaust goes thru drive. Next step is swap some hose like mentioned by Airjunky and probably pull circulating pump and back flush thru block. First time to post pics on forum so if this does not work I will try something else.....

https://s24.postimg.org/je95cl37p/IMG_5057.jpgimage hosting no sign up

I am going to pull riser on the other motor and check to see if its the open water jacket or closed tomorrow.

check the p/s and oil coolers for junk clogging them.

No expert on that style manifold but it seems odd that there is a block off gasket between the manifold and riser. Usually thats for closed cooling systems. Do the risers have separate hoses coming off the T stat housing that go to them.

Chris

Looks pretty clean for some old school manifolds from way back in the day.
A good trs pump will way exeed what a garden hose will deliver, go for the bucket with hose (or2) feeding it .

Thanks Mike Tkach the ps oil cooling was very restricted with rubber from the impellar off the pump, I am going to pull pump again but it must of been from previous owner. I am going to back flush everything I can before going back with it. are the gaskets on the risers reusable? oil change, oil filter relocation, and any other things that need attention. Thanks again for all the help from everyone. yes motors and everything is very clean. Hope to get some use out of it next season.

Would not reuse the gaskets plus I really think they are the wrong ones. You should have gaskets that let some or all of the water through from the manifolds to the risers. Really need a pic of your thermostat housing and hoses to determine.

Chris

You have the correct gaskets.

The SS plate is solid that goes between the gaskets.

If the riser are not hot but the manifolds (logs) are hot then pull the two hoses off of the logs and replace with clear reinforced and fire it up and see what you see.

There must be good water flow through the risers but not through the logs.

GL

1981 I am saying you are wrong but are you sure you are right about the gasket. How does the water exit out of the log and out of the boat if it can not make it past that solid gasket. Here is a replacement set and they have open gaskets.

http://bpi.ebasicpower.com/shop/inde...ducts_id=16415


http://bpi.ebasicpower.com/search_2/...haust+manifold

I am 100% sure.

Look at the SS plate to the right of the log. That piece goes in between the Gaskets.

Virtually no water goes from the logs into the riser.

Water circulates through the logs.

Another water supply goes into the riser and that water then goes overboard.

I tried to pull the riser off the other motor manifold but I need a help and she wasn't home to verify the solid water jacket gasket is correct. I read about this style somewhere recently and the I believe it was the water that goes by the bypass on the thermostat goes thru the logs and back to below the thermostat to circulate thru motor to help heat the motor then there is another hose below the thermostat that goes to the riser to dump out exhaust. I have 4 hoses that are below the thermostat and 2 above the thermostat I will try to take a better pic and verify other motor this evening. 1981Scarb must have the same set up.

here is a link the the parts for that motor, may have to copy and paste it not sure how to make it live.

http://www.crowleymarine.com/mercury...ts/1594_10.cfm

I bore scoped the exhaust pipe after the riser down and expected to see the flapper/shutter in there and the only thing I saw was looked like a bolt running through the pipe about where it connects to the exhaust separator, I took some pics but I am not real good at posting pics, took an hour last time. Is the a shutter on both sides of the exhaust or just where the two come together? Thanks again for everyones help.

Mine has through transom exhaust and the flapper is in the transom exhaust pipes.

WRONG GASKETS unless you have aftermarket go fast exhaust hoses / hose route pics are needed / check all coolers clean / check thermostat , folks say they will fail in open position fail safe safety . Ours even twin t stats have always failed closed solid / BTW run our marine motor with NO thermostat , no circulating pump = much happier / if you need t stat you could run 120 version / 81 scarab - if you do not have proper water flow thru critical parts in a high performance and or marine boat motor I can promise you and or others will blow a lot of motors headers manifolds ALL TO HELL

The gaskets are correct for the Log manifold to the exhaust riser. There are two gaskets that look like they should pass water but they do NOT there is a SS solid plate between them.

If your talking about that gasket.

sometimes back flushing works,sometimes you need to use a coat hanger to push the junk out of the tubes.

or thin needle nose plyers that can grip well - use to pull out pieces on the back side of the oil cooler plus use an inspection mirror and a light. or do what Mike said - also depending on room for either method to pick which way is going to work best per your app.

Cleaned ps/oil cooler, will pull water pump next week and back flush block and probe with bore scope camera, going to pull raw water pump and double check. New gaskets are on order for the exhaust logs to risers. Great information provided thanks to all! Merry Christmas!