Evinrude 5hp

Hadenough

Hadenough

Well-Known Member
Joined
9 Jan 2011
Messages
3,081
Location
No fixed abode
Visit site
We have an trusty 1991 Evinrude 5hp outboard. Start of this season started it the test tank after winter service. Just new plugs, flush and grease this year. after running for five mins the tell tale, pumping like a goodun, started to get hot and eventually was producing steam so I shut it off. Started again after 10 mins and it was pumping as normal but overheated to steam again after 5 mins. I'm assuming a thermostat failure but does anyone know where it is??
 
Unfortunately the American parts lists do not cover a 5 hp for 1991.
Its a European model I guess, built in Belgium

However I think the 5hp is a de-rated 6hp in which case it'll look like this diagram

(I dont think the 5 hp is based on an uprated 4hp. The 4 hp has neither telltale nor thermostat)

You see the thermostat at the top of the cyl head but its called a "Venatherm". #29 in the above diagram.

Check the Venatherm by all means... you'll see its all part of the water pressure control sytem. Be sure to reassemble correctly.

I am puzzled though that the water from the telltale gets that hot with a good flow. Its only been through part of the engine and the telltale is before the thermostat.

But for you saying that there is good flow from the telltale I'd suggest its time for a new impeller. When was it last changed?

The grommet at the top of the watertube can be a PITA in some of these Evinrude models ( Dont ask how I know)

The water passages in the cylinder head can easily become blocked as well.
 
Last edited:
Hadenough said:
We have an trusty 1991 Evinrude 5hp outboard. Start of this season started it the test tank after winter service. Just new plugs, flush and grease this year. after running for five mins the tell tale, pumping like a goodun, started to get hot and eventually was producing steam so I shut it off. Started again after 10 mins and it was pumping as normal but overheated to steam again after 5 mins. I'm assuming a thermostat failure but does anyone know where it is??
Click to expand...

I'm not going to say it is the same thing, but I have just had this same problem on my 4hp Twin, so the engines may not have the same head arrangement.

Mine would give a good flow, but then overheat with steam and smoke!

After taking off the side plate to the exhaust BE4BREDS on my engine, part number 18, I found that the exhaust cover plate had a corrosion hole in it between the waterway and the exhaust gas side under the gasket.

Subsequently, the water would come through, but then be overcome by the exhaust gas and come out as steam and fumes.

I fitted a new plate and gasket, and now get cool water out and no overheating.

As I said, may not be the same as yours, but something to look at.
 
Thanks Vic and Phil.

info, diagrams and links appreciated. You are perfectly correct Vic it is a Belgian engine the engine no is BE50REIA, serial no 08813322, sorry should have quoted them before. I intend to double check the new plugs to make sure they are correct and gapped properly as a first (easy) port of call. Now I know where the thermostat is I will try trial and error with it out. The impeller is a couple of years old but the tell tale has always pumped like a fire hose and still does until it goes to steam. Must say though that it sounds very similar to Phil's experience. Five mins running then the tell tale turns to steam but I have been cutting it out straight away so have not experienced smoke! what is really strange is that starting it a few minutes later it is back to normal for a few minutes then the tell tale turns to steam. I'll have a look at the exhaust plate now too. I'm not with the boat again till Good Friday but I'll keep you posted. Thanks again.
 
My BIL had the 7.5hp which (I am sure) is the same as the 5hp. It had the similar symptoms. The grommet at the top of the water tube had swollen and closed off the passage. (I don't think you would get a pee stream if that had happened, however, if you have to split the head/leg joint fit a new one).
He didn't have a thermostat in the housing and they give dire warnings about not having one. It's as much to do with providing the correct flow and wash in the cooling system as it is about temperature control.
The new ones are eye-wateringly expensive (about £50 if I remember).

The corroded plate sounds very plausible.

Don't bother checking the plugs. It runs and they wouldn't cause the overheating you are experiencing.
 
I intend to double check the new plugs to make sure they are correct and gapped properly as a first (easy) port of call.
Click to expand...

As for the plugs i am pretty sure they will be Champion QL77JC4 ( in 1991 QL77J4 may still have been around but if so its now replaced by QL77JC4.

However the point is that the Q means they are inductively suppressed, and are special plugs for the OMC CD ignition system.

If you cannot get Champion plugs and have to settle for NGK the correct equivalent is BZ7HS-10. The Z indicates inductive suppression

DO NOT use the resistor plugs BR7HS-10 or any other plug with an R in the number. R means resistor suppressed.

Unsuppressed B7HS-10 would be preferable.

The -10 BTW means that the come ready gapped at 1.0mm.

OMC revised all the plug gaps in the 1990's from 0.040" ( 1.0mm) to 0.030" (0.7-0.8mm). If your manual says 0.040" / 1.0mm its up to you. The usual advice is to use whichever works best. I cannot tell any difference.


I think your 5 hp will have a water cooled exhaust cover plate as in the diagram I gave earlier. The diagram for the 4 hp shows an uncooled cover.
 
Going back to the plug. I checked he latest available list. It gives the plug as QL86C.

Same comments apply regarding the "Q"

There is no NGK equivalent listed but you may be offered BR6HS.

Same comments apply about "R" plugs. You'd be better with B6HS
 
Just going back to your original problem and following on from VicS

There are two outlets (usually on the left as you look from the back of the engine, if your unsure, just follow the tell tale tubing) out of the head. It is quite common for one of these to be blocked, only allowing one cylinder sufficient cooling and the other to increase pressure and give you a good tell tale.

To check this, pull off the tell tale tubing from the head at both points and check your flow coming out of these. If it is blocked, try and clean it out. I use a largeish syringe to force air back through the system at high pressure.
 
monkfish24 said:
Just going back to your original problem and following on from VicS

There are two outlets (usually on the left as you look from the back of the engine, if your unsure, just follow the tell tale tubing) out of the head. It is quite common for one of these to be blocked, only allowing one cylinder sufficient cooling and the other to increase pressure and give you a good tell tale.

To check this, pull off the tell tale tubing from the head at both points and check your flow coming out of these. If it is blocked, try and clean it out. I use a largeish syringe to force air back through the system at high pressure.
Click to expand...

Are you sure?

I am expecting only one telltale running from an elbow on the exhaust manifold cover to an outlet in the rear stb side corner of the lower cover.
 
Belgian engine the engine no is BE50REIA, serial no 08813322,
Click to expand...

I only just noticed. That model number should read BE5DREIA ( otherwise it indicates a 50hp engine!)

B= made in Belgium
E= Evinrude
5 = 5hp
DR = derated, rope start
E = 9, I = 1 ( hence '91)
A is a production suffix

I though I would point that out to you in case you ever need to order parts.

FWIW Oakley Marine in Brighton and Willsmarine in Kingsbridge are both good for mail order parts.
 
Yes just one tell tale, from memory, didn't have space to bring the OB home with me!
How about this for a theory from a motor bike mechanic friend?
Engine starts up and pulls up a plug of water though the impellor into the cooling system, good squirt of water from tell tale because it is downstream of the block and thermostat. Thermostat, just upstream of block, jammed / seized shut. Plug of water sitting in waterways of block cools at first but having nowhere to go past the jammed thermostat, overheats, backs up and and produces steam from tell tale. Engine is stopped, immediately restarted and whole process repeats. To the best of my knowlege there is no non return on the system and it relies on an unimpeded flow through the waterways via the thermostat to exit down the leg and blend with the exhaust.
This may explain why when I restart straight away after the steam effect it initially produces a good flow from the tell tale and repeats the overheat cycle within a few minutes.
Just a theory but worth a look with the other pointers you guys have suggested. Thanks again, I'll let you know how I get on.
By the way have checked my receipts and the plugs were replaced like for like with NHL BZ7HS-10. Think I need to check the engine number again though it's not a 50HP (unfortunately, because our mooring is 2 miles from the slip!!)
 
Hadenough said:
Yes just one tell tale, from memory, didn't have space to bring the OB home with me!
How about this for a theory from a motor bike mechanic friend?
Engine starts up and pulls up a plug of water though the impellor into the cooling system, good squirt of water from tell tale because it is downstream of the block and thermostat. Thermostat, just upstream of block, jammed / seized shut. Plug of water sitting in waterways of block cools at first but having nowhere to go past the jammed thermostat, overheats, backs up and and produces steam from tell tale. Engine is stopped, immediately restarted and whole process repeats. To the best of my knowlege there is no non return on the system and it relies on an unimpeded flow through the waterways via the thermostat to exit down the leg and blend with the exhaust.
This may explain why when I restart straight away after the steam effect it initially produces a good flow from the tell tale and repeats the overheat cycle within a few minutes.
Just a theory but worth a look with the other pointers you guys have suggested. Thanks again, I'll let you know how I get on.
By the way have checked my receipts and the plugs were replaced like for like with NHL BZ7HS-10. Think I need to check the engine number again though it's not a 50HP (unfortunately, because our mooring is 2 miles from the slip!!)
Click to expand...

That sounds about right, the tell tale coming out is high in pressure as the thermostat is closed. The tell tale I would expect is from a by pass that keeps water flowing past the impellor.

As the thermostat opens (which yours isn't), the by pass drops in pressure as the waterways open and are cooled. The tell tale will remain the same pressure as you will now have two flows, one from the by pass and one from the thermostat.
 
Hadenough said:
Yes just one tell tale, from memory, didn't have space to bring the OB home with me!
How about this for a theory from a motor bike mechanic friend?
Engine starts up and pulls up a plug of water though the impellor into the cooling system, good squirt of water from tell tale because it is downstream of the block and thermostat. Thermostat, just upstream of block, jammed / seized shut. Plug of water sitting in waterways of block cools at first but having nowhere to go past the jammed thermostat, overheats, backs up and and produces steam from tell tale. Engine is stopped, immediately restarted and whole process repeats. To the best of my knowlege there is no non return on the system and it relies on an unimpeded flow through the waterways via the thermostat to exit down the leg and blend with the exhaust.
This may explain why when I restart straight away after the steam effect it initially produces a good flow from the tell tale and repeats the overheat cycle within a few minutes.
Just a theory but worth a look with the other pointers you guys have suggested. Thanks again, I'll let you know how I get on.
By the way have checked my receipts and the plugs were replaced like for like with NHL BZ7HS-10. Think I need to check the engine number again though it's not a 50HP (unfortunately, because our mooring is 2 miles from the slip!!)
Click to expand...

Something like that maybe, but the water flow is not quite as you imagine.

Water enters the block, flows through the block and the exhaust manifold cover. The tell tale is from this this cover. Then via the thermostat/pressure control valve to the head. Finally discharged into the leg from the bottom of the cylinder head.

Check the thermostat as thats an easy thing to do.

Be prepared for the water passages in the head to be blocked solid!

Because the system is pressurised you will get a normal flow from the telltale even if the pump impeller is getting poor or if the grommet at the top of the watertube is restricting the flow.

Be prepared to tackle both of these.

That grommet is a PITA and it needs both gearcase off and power head off to renew it.


Lakesailor has some photos of a similar engine he sorted out for his BIL. Head was blocked and the grommet blocking the flow too IIRC. Don't know if I can find them now.
 
A couple of Lakey's pictures

The grommet:

Watertubegrommet.jpg


The head after cleaning out the figure of 8 water-ways

JonhnsonHead.jpg
 
Last edited:
Thanks for pics. I can see why the grommet is such a PITA. Looks like I'll be bringing the OB back to the workshop if the easy wins don't work. Two mile row to the mooring, better get the tide tables out!
 
Got it sorted eventually. Decided to bite the bullet and get the head off to look at the waterways. So side plates off, head off, thermostat out, everything replaced with new gaskets. £50 the lot from Willsmarine (thanks VicS). Waterways weren't too bad but did need clearing, (funny waxy gung must stop using the club flushing tank I think). Main problem turned out to be the head gasket blowing between cylinders. Explains why it was always a pig to start from cold I think. Thermostat cup housing was cracked / chipped too which may have contributed to the severe overheating. Anyway ---- new outboard!! Starts second pull from cold, runs much smoother, (I always put the lumpyness down to cavitation before) and I think gives more power. Thanks for the pointers everyone. Moral of the story --- OK it cost me £50 but at the end of the day the refurb only took an hours work once I decided to stop poncing around and strip it down!
 
You must log in or register to reply here.

Share this page

Top