v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead pan?

[pcrussell50]

I have three v4 crossflows. One is a frankenstein that started as a 90 block, but now is ported and has wiseco pistons and 140 carbs, and a bubbleback, etc... on that motor i'm trying to chase down a _possible_ overheating problem, and i'm trying to eliminate all variables before i dive into the HUGE pain of a thermostat change, (because it's a bubbleback).

anyhow, when i tie her up to the dock while idling, after a few minutes of idling, water is basically gushing out those relief holes. this does not happen on my all stock, good running, 1975 135. that one can idle a long time, and only gets spits and sputter of water out those relief holes.

so what i'm asking, is:

1) what does it mean when water comes gushing out those holes?
2) what are they for?
3) how do they work?
4) since i'm trying to avoid a thermostat job, when water comes out those holes, does that mean the thermostats are opening normally?





further info about my possible overheating:
1) the alarm never sounds while idling or on the low power circuit
2) it sounds continuously at mid-power cruise, like 4000 rpm
3) then it silences again at higher rpms like 5000+

Also, I pulled the starboard head and looked at the cooling passages and they are sparkling clean, with no blockages. The rubber flow diverter is there too and looks good. I have not pulled the port side head yet.

What can you gurus tell about this?

-peter

 

[keefallan]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

What is the year of the midsection for it? That will matter. In '75 the won't have water come thru there. It has to do with the way they designed the cooling system for those years. The 75 135 doesn't have the same cooling system. It sounds to me that the ported motor has a late 70's early 80's midsection. I don't know when they changed it to the newer style(when in the 80's). I have a 235 with a '79 midsection and water rolls out those holes.......it's meant to. Now, on the newest style midsections that is not the case. It's just cooling designs. Sounds like time for some stats to change. What about your impeller?

 

[pcrussell50]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

aha. i wasn't aware the three different mids operated differently from a cooling perspective. i would have guessed they would all be the same as far as cooling is concerned. the mid in question is a 1980 or so.

does the water rolling out the holes on the mid-generation mids while idling, have anything to do with the thermostats opening?

-peter

 

[Joe Reeves]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

(Exhaust Relief Ports - Exhaust Housing (Inner/Outer)
(J Reeves)

The long housing between the powerhead and the lower unit is called the exhaust housing. There is a inner housing within it that has a heavy duty seal around the bottom of it, or heavy duty seals around a inner extension between the housing and the lower unit.

The red hot exhaust travels down thru that inner tube and out the propeller with a somewhat supply of water to cool the propeller hub. A good amount of water surrounds and fills the space between the outer and inner tube, otherwise the outer housing would get so hot that the paint would burn off.

Some water pumps, for some reason (differing even when new) exert a great amount of water pressure, and if the exhaust housing seals are in perfect condition, the water fills the tube to a point of overflowing.

This brings into play those two holes or slots, whichever the engine might have, at the top rear portion of the exhaust housing just below the powerhead.

Now, if those two holes/slots weren't there, water would continue to flow up into the cylinders. Water not flowing out of those holes is no concern for alarm UNLESS that outer housing suddenly becomes extremely hot..... the warning horn should sound long before that happens.

The main reason for those holes being there (exhaust relief holes) is that when at an idle, there is an extreme amount of resistance encountered by the exhaust trying to escape due the fact that the outlet via the propeller is now blocked by a wall of water. The escape route in this case is for the exhaust to escape out those two holes, otherwise the engine would slow down quite quickly and die. If exhaust cannot escape, air/fuel cannot gain entrance to the engine.

 

[emdsapmgr]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

You are working with two different models. The early V4 crossflows used one thermostat, called a vernatherm. Up through the 1977 models. On those units only expect a light mist out of those exhaust relief. These early V4 crossflows used a single thermostat. If you start the engine cold, hold the palm of your hand back by the exhaust relief ports. After a minute, the vernatherm will open and you will get a light mist that will form on the palm of your and. That's normal. In 1978, OMC re-designed the block and exhaust adapter to use two thermostats. During the redesign of the block, significant water flow comes out of the exhaust relief ports after the stats open. Also, when you are up on plane, the pressure relief valves will open and you will get two huge streams from those ports. If you have replaced the stats and still have cooling issues, double check the following: There is a plastic valve body inside the (dual stat) thermo housing-up to around the 1990-1991 models. It has two tiny pinholes in it. Those have to be open or the block will overheat. Inside the block are four rubber diverters (called deflectors). They have to be properly positioned or the water flow through the block can get impeded/restricted causing an overheat.

 

[pcrussell50]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

as i live and breathe... two of the heaviest hitters in the v4 crossflow world have responded to li'l old me. thanks, guys.

emdsapmgr, (sorry, i've "known" you for years and don't know your name)... now we're getting somewhere.

you said:

During the redesign of the block, significant water flow comes out of the exhaust relief ports after the stats open.

since i'm getting significant flow of water out the relief ports during idle after warmed up, can i safely assume that my thermostats are opening normally? in short, when cold, water does not come out the relief hole at idle, and when warm, it comes out significantly at idle.

further, i had BOTH heads off today and the diverters are properly in place, clean and solid, (not deformed), and the water passages in the heads are clean. they are in the right places too, according to my factory service manual.

does it make any sense to you that the buzzer does not sound at idle or at high rpm... just mid range... 3000'ish to 4500'ish rpms?

-Peter

 

[Faztbullet]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

The water sound come and go at a idle not continuously once t-stats open. Once you get above 2500-3000- rpm the poppets open and bypass the t-stats. Your overheat alarm at 4000 rpm could be: lean cylinders, base gasket under water pump plate, blockage in a cylinder head. Remove the lead from one cylinder to narrow it down to what side is triggering alarm, If you can narrow it to a side its a cooling issue, if not its a timing/fuel possible porting issue.

 

[emdsapmgr]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

If you are still having cooling problems, take the head covers off the heads and see what the water passages look like inside. If the engine has been run in salwater, those passages could be restricted. Keep in mind, whatever you find inside the head passages will also be found inside the block. That includes the main water galley between the heads. (under the water cover between the two heads -on the top of the block.)

 

[Joe Reeves]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

since i'm getting significant flow of water out the relief ports during idle after warmed up, can i safely assume that my thermostats are opening normally? in short, when cold, water does not come out the relief hole at idle, and when warm, it comes out significantly at idle.

No, observe the holes/slots at lower unit, in particular the holes/slots just above and to the rear portion of the cavitation plate. Those holes are the water outlet for when the thermostat(s) open. Water will not flow out those holes/slots unless the thermostats are open.

 

[dsujen]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

I had a 1986 110hp evinrude bubble back. I cut a rectangular hole in the lower cowling to get to the thermostats easily. When done, I tack welded the panel back on and bondoed it. I was not going to remove the power head for a thermostat job.

 

[emdsapmgr]

Re: v4 crossflow: explain the cooling/exhaust relief holes just below the powerhead

I agree that the bubble back V4 engines are sure to give you skinned knuckles when you change the stats in that thermostat housing with the powerhead in place. The factory flat rate manual gives something like 3.0 hours to pull the powerhead to replace the innards in that housing. Most skilled mechanics with a 1/4" drive socket set with a swivel would not pull the powerhead, preferring to swear at it instead- while they open it with the powerhead mounted in place. They will do that job in half the flat rate time.