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SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 7:50 pm
by Hardtail
I'm not sure what is the problem, but I'm sure somebody on here knows what could be the problem, the last time I ran it was last November, and when I would try to move the airboat at around 4800 RPM on dry ground, it would rev up to try and go but then suddenly the RPM would drop to Idle and almost die but would recover and rev up again only to do that again, the overflow tube from the cooling system would be spewing coolant, so then I shut it down thinking maybe a water pump problem, also before this when I ran it down here in the Sun Shine State, I noticed it to be getting hotter sometimes, and removed the thermostat which did not make any difference, so I put in a new 180* thermostat ran it and seemed fine until I got to Minnesota with it then it started this rev up only to almost die then rev up and almost die again, QUESTION ? could this be cooling system problem or Cracked head, No water in the Oil showing, So Hunting Season is coming up again this November and I'm going up there needing an airboat to get to the hunting area.
Anyway it is 350 SBC with 2 to 1 Belt reduction on a combee fiberglass with poly, 2 blade Sensenich. When I first bought it, it would go anywhere I wanted, up ditches, down paved highways, with no problems, now something needs fixing, any help would be greatly appreciated, THANKS

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 8:37 pm
by terrible ted
more details carb

Is it running out of fuel are you letting off when it dies and then it recovers. collapse fuel line sucking closed bad on the inside?

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 8:39 pm
by scottyroll
What kind of fuel pump are you running? Is it regulated and working properly?

Does any smoke come out of the pipes when it revs up then dies?

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 8:44 pm
by terrible ted
check oil and water make sure both are clean.
check all water hoses cap
is this new or old boat and problem just started?

how's it running at idle
you said you put in a t-state open at right temp

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 8:45 pm
by blow boat
yeah need more info sounds like fuel and cooling system issue
replace fuel filters check lines check plugs and also fuel pump
that would be a good start

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 9:11 pm
by barhopper
I had a blown head gasket on a SBC that was pressurizing the coolant system causing coolant to come out the overflow but it took a while to build up. Don't have a clue about the rpm problem but sounds like a fuel issue.

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 9:31 pm
by Hardtail
Yes it has a Carburetor, and doesn't take long for it to blow coolant out the overflow hose even at idle, I did have the carb cleaned by Banner Tire in Miami before I took it To Minnesota, I bought a new water pump to put in when I get up there at the end of this Month, but I'm thinking now that it might not be that, could it be cracked head or blown head gasket?

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 9:38 pm
by Hardtail
Put new hoses and radiator cap on it last year before I took it up there, Has an Engine driven fuel pump with an electric one on a switch just to get the gas up to the engine pump.
The Temp gage goes all the way hot when the RPM's drop off,
The Oil is clean, not milky, the coolant blows overboard through the overflow hose

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 9:56 pm
by terrible ted
Any water in oil?

The motor can over heat fast if the cooling system is not burped. how is the system plumbed? yes a head gasket can do it to.. The highest part of the cooling system needs to vent air. pictures might help. my last 350 had a hose right off the top of the T housing to a burp tank. with out it it spews coolant because it cant circulate due to air trapped in top of motor.

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 9:59 pm
by terrible ted
a manual pump shoud not need electric pump.

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 10:01 pm
by terrible ted
all plugs look good

Re: SBC 350 with overheating issues

Posted: Wed Oct 07, 2015 10:34 pm
by Hardtail
I'll be up there in 3 weeks to have another closer look at it, would like to know how to burp the cooling system, I'll pull the plugs and see, going to put on the new water pump being I already bought it anyways, if it is a blown head gasket, how would I know ?

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 7:28 am
by Scotty1
:rebel: as for the rev problem try turning on electric fuel pump with the manual pump sounds like not getting enough gas , as for the heating when you first start the motor remove the radiator cap and see if the water is circulating , you may have to wait a bit for the thermostat to open :rebel:

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 7:46 am
by terrible ted
Hardtail wrote:I'll be up there in 3 weeks to have another closer look at it, would like to know how to burp the cooling system, I'll pull the plugs and see, going to put on the new water pump being I already bought it anyways, if it is a blown head gasket, how would I know ?
picture of the system. look at the system can it trap air. rad below the motor - weres the fill tank how does the air get out of the motor. if some had running before it probably good. My boat use to have a problem like that part of the problem was water no circulating up at the t-state. I always wanted to add a race style t housing with a cap

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 8:32 am
by RJC5778
dumb question....does it have fresh gas in it? the high rev then die sounds similar to water in fuel

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 9:17 am
by Hardtail
Yes the gas could be 2 years old, found a picture of the boat, a picture is worth a 1000 words,

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 9:26 am
by Hardtail
starboard

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 9:28 am
by Hardtail
Starboard rear pic

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 9:32 am
by Afflicted
My opinion on the revving deal is the gas. When I was replacing my motor, I had the same gas sitting in the tank for only 5 months and I treated it with seafoam and stabil.... When I got new motor on it ran like crap. Long story short it was the gas. It wasn't even very flammable with a lighter
When u get there buy a gallon of gas and stick your fuel line in it and fire it up

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 9:47 am
by Hardtail
Question: So you don't think the overheating and the engine RPM's going to idle and almost quitting are the same problem?
Could be 2 different problems, I would like some tips on how to get the air out of system,
I'm going to put on a New water pump, Fresh Fuel, Fuel water separator filter, New Belt for the water pump/alternator...anything else???
I'm not sure if the radiator has a cap, I think the only cap is on the little tank (overflow reservoir) that is on the cage above the engine, which that small hose you see in the picture goes up to.

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 10:57 am
by RJC5778
being that you are running a thermostat, your engine may be air locked.....try to "burb" the coolant and get rid of the tstat, run a restrictor washer, keeps engine cooler, and or just open water neck, my setup is similar to yours with the radiator at the bottom and a burb tank at the top, yes fresh fuel is a huge help and also verify timing on engine, that can cause overheating issues as well, do all your basic engine checks and eliminate any obvious issues and youll find you problem

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 4:13 pm
by Hardtail
Thanks for the all the replies and help,
Now my question is whether or not to tow my 0 360 Frannie Taylor airboat up there just incase we can't get the car motor to run us across the swamp,
I'm wondering if there would be a fair possibility that one of the heads could be cracked or a blown head gasket, if it were only the bad fuel and a burp I could get that done, but if it needs to be
taken apart hunting would be over : (
The more I learn about car motors on airboats the more I like my Lycoming. LOL : )

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 5:00 pm
by RJC5778
do your basic checks and go from there. running that motor hot often will inherently crack the heads or blow a gasket, check for oil in coolant and vice versa, if you are uncertain about reliability that should answer your question IMO.....car motors are not bad, AC or CM require the same amount of love and care, its just a machine, CM are easier to work on IMO and easier to fine parts for at a cheaper cost

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 5:38 pm
by Hardtail
RJC5778 wrote:do your basic checks and go from there. running that motor hot often will inherently crack the heads or blow a gasket, check for oil in coolant and vice versa, if you are uncertain about reliability that should answer your question IMO.....car motors are not bad, AC or CM require the same amount of love and care, its just a machine, CM are easier to work on IMO and easier to fine parts for at a cheaper cost
Yea I know,
I have my AC airboat in my yard and can tinker with it everyday after work if needed, just that the car motor one is 2000 miles away and I can't work on it until I get there or tow it back to Miami to work on if needed, just can't tow them both back at the same time if I tow this one up there. I'm learning more everyday from this site, I love this site because we have such great members who are will to share information and experiences, just my frustration showing.

Re: SBC 350 with overheating issues

Posted: Thu Oct 08, 2015 5:42 pm
by glades cat
It looks like your thermostat housing is the highest point in the cooling system. Drill and tap a 1/4" pipe thread and install a 1/4 turn brass valve on top to get rid of the air. Bleed air until coolant comes out. Be sure and drill a 1/8 hole in the thermostat to bypass coolant until it opens.
Also test the coolant for products of combustion with a kit. I suspect a blown head gasket. It's very cold where you're at. Make sure you do a good warm-up before running the engine hard. Things contract and swell a lot more than they do in S FL.
Good luck Bruce.