5.7 overheating at idle

[JOEP2]

I have a 90 baja 190es boat with a 5.7 SBC with some performance work done to it, cam, light head porting and alum intake. The motor was rebuilt over the winter of 2010. It also has new exh risers and manifolds,with thru haul exh. new engine water pump and so on. My problem Im having is it overheats from idle to about 2000+/- rpms when under way. Also on the muffs on the trailer. I didn't rebuild the motor and Im also going by the previous owners receipts from when I bought it from him. Its overheated like this from day one, so from some reading I thought it was the lower unit impeller pump. I took it down an found that at one point someone else has replaced this but must have had a issue getting it off so they used what looks like a cut off wheel to get the old impeller off and in doing so, cut a groove in the shaft. I went ahead and replaced the impeller anyway and when installing the rubber seal that goes on the top of the impeller housing Im finding that the groove cut in the shaft actually keeps the seal from doing its job. When running on the muffs I removed the hose from the outdrive to the thermostat hosing and its not a steady flow of water, more of a pulse then steady, but is flowing pretty decent. under load and running the temps stay 140-150 but idling up the canals it overheats up to 200 deg.
First I guess my question is, is the reason my motor overheats at low rpms? and second can I just weld up the groove and smooth the weld out and be ok? also is the shaft stainless steel or polished steel of some sort?
Im hopping to save the shaft cause I cant afford a rebuild right now and Im a certified tig welder an can weld it up myself.

 

[dollarten]

Re: 5.7 overheating at idle

First off , don't do any welding on the drive shaft. Some are stainless , some are chrome plated It will be a lot of work to reproduce the original finish and if you weld on it you could cause some warpage You will also need an assortment of special tools to work on the drive unit....>> If you look at the water pump stainless insert , you will see that it will seal itself and . water will not escape through the top area that you are looking at . The only way you will have a pressure loss is if any of the water pump surfaces and passage ways are damaged

 

[JOEP2]

Re: 5.7 overheating at idle

I understand what your saying. About the impeller but I'm at a lose with this got any ideas as to what I should check? I'm going to pull the engine water pump next an see if there is any issues there. I do now my risers are fine. I just had them off an there clean as a pin. Could the wrong water pump pullies be something that would cause this? Again I feel like I'm beating my head against a brick wall.

 

[NHGuy]

Re: 5.7 overheating at idle

Hi, I have a stock setup with a similar though less problematic issue. With mine I can get the temp down from 180 or 190 by bringing the rpm's up over 1100. I get a creeping temp increase when at idle after the 1st year with an impeller. From what I have seen this is not that unusual. Apparently the Alpha 1 lower has just so much water it moves, but once you pick up the revs there is quite a lot more water. I swapped out my impeller this fall after burning around 120 gallons of fuel this summer, and a little less the year before. It was pretty hard and bent over so I am sure it didn't make the tightest contact with the housing. That's why it doesn't do as well as one that's new.
You say the motor is slightly worked over. Does it have a lumpy low idle? Reason I ask is you say the lower unit water supply seems to spurt. Am I getting this right? Try running the motor at 1200 Rpm and see if there is a significant increase in flow. My stocker, which runs very smooth, cools in seconds with 11 or 1200 rpms. Even on that old hardened impeller.

Don't bother to do that til you have really checked over what you have though. You'll need to open up all the cooling passages and check em for blockages. I'd start with the port side of the engine where you should have a water to oil cooler for the power steering. Back flush or blow that out. Also, there is a fairly small tube where the water enters the boat from the lower unit to transom hose. I haven't had trouble with mine but it's only about 5/8" diameter and has barbed ends. Crap can catch on obstructions. Remove and clear every cooling passage you can. If some previous user had a piece of impeller get in there it can cause havoc. Inspect, blow out and backflush every passage you can. It might be the solution, and it's the right thing to do anyway.

Is your compression ratio way up? That makes heat. If you are running a motor that is hot in and of itself with the Alpha leg pump you may need to get a separate through hull pickup and seawater pump. That involves more parts and money. Once you are just positive there are no obstructions it might be the move to make.

If you are positive the groove in the shaft is bypassing water that is lousy. It would be great if you could try someone else's lower. Not much chance to borrow one though.

 

[Bondo]

Re: 5.7 overheating at idle

I understand what your saying. About the impeller but I'm at a lose with this got any ideas as to what I should check? I'm going to pull the engine water pump next an see if there is any issues there. I do now my risers are fine. I just had them off an there clean as a pin. Could the wrong water pump pullies be something that would cause this? Again I feel like I'm beating my head against a brick wall.

Ayuh,... Take it easy, yer gonna bust up that wall...

You've got a Frankenmotor, Pictures would help...
We'd like to see the plumbing lay-out...

I doubt it's the circulating water pump...

Pull the line comin' in from the drive, 'n put in a length of clear hose, 'n start it...
You should see clear water, No bubbles...

Does yer T-stat housing have the check-balls in the exhaust water fittings/ barbs,..??

 

[CharlieB]

Re: 5.7 overheating at idle

When running on the muffs I removed the hose from the outdrive to the thermostat hosing and its not a steady flow of water, more of a pulse then steady..........................

It should be a very steady flow, directly increasing with any increase in motor speed.

JD Weld the shaft to fill in any gaps without any worries of warping it.

Re-inspect the water pump housing, the stainless cup and plate often wear a 'ring' into them from the raise seal on the side of the impeller, if you can feel this ring worn into the metal around the center hole for the shaft to pass thru, then it is time to order a complete rebuild kit.

Also double check the pump housings, top and bottom, to be sure they are not warped and sucking air in between the housings.

 

[JOEP2]

Re: 5.7 overheating at idle

I do have a loby cam installed, i dont know the exact specs on it but it does sound nice I checked the hose off the outdrive going to the thermostat housing both before and after the Impeller swap and I ended up with the same water flow/surge results after the replacement impeller kit. I have also completely drained the block and checked as best I could for debree and found none, risers are new and clean. There was a set of check balls in the thermostat housing and they seemed ok. I did remove them just to see of it made a differnce and it didnt, i also pinched the same hoses to see if that made a diffence and it didnt, still overheated. I think the only thing I havent checked is the engine water pump.
Looking thru the service manaul I have I did see several ways the water hoses are ran on the alph 1 5.7 motor set up, and did see where there is a verson of this with a remote water pump mounted to the engine drivin by a belt. is this what Im suppose to have?

 

[Bondo]

Re: 5.7 overheating at idle

is this what Im suppose to have?

Nope,... That's for freshwater coolin' with a heat exchanger...

Put the check-balls back in, they're Necessary....

What's yer idle rpms,..??

That lumpy idle might Sound cool, but it's probably gonna bite ya in the ___, if it ain't already....

 

[JOEP2]

Re: 5.7 overheating at idle

Idle rpms are about 900-1000rpms, the balls are going back in this weekend when I get time to work on it again. If I let the idle go any lower it will stall out when I place it in forward or reverse.

 

[Bondo]

Re: 5.7 overheating at idle

Idle rpms are about 900-1000rpms, the balls are going back in this weekend when I get time to work on it again. If I let the idle go any lower it will stall out when I place it in forward or reverse.

Ayuh,.... Yer lumpy cam Is already bitin' ya,...

Yer drive will be scrap iron in no time at that idle....
You need to get it down to 650/ 750 rpms, at idle, in gear, in the water...

Otherwise, expect to be replacin' the drive,... Regularly....

I checked the hose off the outdrive going to the thermostat housing both before and after the Impeller swap and I ended up with the same water flow/surge results after the replacement impeller kit.

Did ya Back-flush it while the lower unit was off,..??
There could be old debris from a failed impeller stuck in there...

Just the fact that it's surging, says the Problem is between the raw water pump, 'n the T-stat housing...

 

[JOEP2]

Re: 5.7 overheating at idle

I did back flush and it was clear. There is no way I can get the idle down that far, it wouldnt stay running at that point. In gear and underway idle is 900-1000 and that is the best I can get out of it. Ive seen other go fast boat do the same idle range and never had any issues, not saying your wrong just confused on that.

 

[Scott Danforth]

Re: 5.7 overheating at idle

i would post pics of the plumbing. if your in salt water and the engine and drive are not flushed regularly, a build up of salt will insulate the block from the cooling water.

In many types of fresh water, mineral content will also foul the cooling system.

does your engine actually reach high temps, or are you relying on your temperature gauge (the cheapest electrical gauge in the dash connected to the cheapest automotive sensor there is)

changing the cam also changed the heat rejection of the engine. couple that with the fact that at low rpm's the cooling water flow is significantly reduced.

 

[JOEP2]

Re: 5.7 overheating at idle

Ill post some pics saturday, by time I get home from work its already dark and its dark when I leave. The motor inside is clean as a bell, theres only maybe 30 hrs on it all in brackish water, I just moved to Florida an have only had it in salt water 1 time for about 2hrs max so far.I also run the boat on muffs both before I go launch it an when I get back to flush it out, both for a min of 15mins. I did do some searching and Im really hoping its as easy as reinstalling the balls and I also stretched the springs out some since it did feel all fully soft. Im also going to drop the lower unit and jb weld up the groove that the first guy cut in it removing the impeller. My thinking is if Im already turning 900 rpms at idle and everyone suggests that 650-700 is where stock should be Im already turning the impeller in the lower unit more then what stock would be a should be pumping that much more water to the engine. My cam isnt a full on race type cam as far as I can tell (also run a drag car for fun for the past 20+ years) and I also verified the temps on my gauge with a heat guy, the gauge is off +/- 3-5degs but still close enough for me to get a really good idea of when shes hot. got my fingers crossed

 

[joewithaboat]

Re: 5.7 overheating at idle

Could be getting air locked??? Drill a 1/8 inch hole in the t-stat if if doesnt already have one.
Also dont serpetine water pumps run backwards??? Maybe has wrong pump?

 

[NHGuy]

Re: 5.7 overheating at idle

1990 should be a v belt drive.
You'd be smart to do the clear hose check, it's a good telltale to see if there's air in the cooling water.

They sell it at the hardware store.

 

[joewithaboat]

Re: 5.7 overheating at idle

1990 should be a v belt drive.
You'd be smart to do the clear hose check, it's a good telltale to see if there's air in the cooling water.

They sell it at the hardware store.

I understand that the original boat is v-belt but gm had some serpentine as early as 84 or 85 I think, in 88 on trucks for sure. They will bolt up and are the same on the outside. A friend who had multiple pumps on the shelf one time mistakenly put a v belt pump on his serpentine truck.... it overheated at idle rpm's only, sounds wierd i know you would think it would get worse at higher rpm... i guess the impeller spinning backwards "Fast" will move water.

The clear hose is a good idea!

Also seen folks talk about a melted/deformed transfer tube in upper part of drive... lets air in the system?

 

[bones774]

Re: 5.7 overheating at idle

Ayuh,... Take it easy, yer gonna bust up that wall...

You've got a Frankenmotor, Pictures would help...
We'd like to see the plumbing lay-out...

I doubt it's the circulating water pump...

Pull the line comin' in from the drive, 'n put in a length of clear hose, 'n start it...
You should see clear water, No bubbles...

Does yer T-stat housing have the check-balls in the exhaust water fittings/ barbs,..??

Re; Clear hose, do you know what size should be used(boat is stored far from house and would like to have parts in hand) and what if we see air bubbles?
what are the check balls?
Thanks

 

[Bondo]

Re: 5.7 overheating at idle

Re; Clear hose, do you know what size should be used(boat is stored far from house and would like to have parts in hand) and what if we see air bubbles?
what are the check balls?
Thanks

Ayuh,... I wanta say it's 1" hose, but it could be 1, 1/4",....
Don't remember for sure...

The check-balls are in the T-stat housing on the out-goin' lines to the manifolds on most older Alpha drive motors...
They hold water back in the motor at idle, rather than it flowin' outa the block...

 

[JOEP2]

Re: 5.7 overheating at idle

If Im on the muffs with the garden hose will this also be a clear hose check? Or do I need to be in the water with the complete outdrive sumerged in the water?

 

[Don S]

Re: 5.7 overheating at idle

The clear hose test has to be done in the water, not on muffs. Not sure it's worth much on an alpha drive since the pump is under water with no chance of sucking air, and any leaks on the pressure side won't cause bubbles.

It's also possible the raw water pump housing or lower housing is warped or damaged, maybe burned. Did you inspect them