70hp vro -89 overheating

[Gabbu]

First some background information, so bare with me.
Last fishing trip my engine was overheating, so the S.L.O.W mode kicked in. I was surprised since I had done a telltale relocation to the top of the cylinder block (on the exhaust side) and fished successfully for a whole year. 55 motor hours.

I had an impeller kit at home and I now decided it was time to install it, so I did.
What worries me is that the old impeller looked ok (normal tear, slight bend on the fins). I didnt finds anything unusual except for that there was no gasket underneath the impeller plate. Hmm? According to my service manual's blueprint there shouldn't be any (?!) but since my kit included one I decided it was best to put the new one on with some gasket sealer.

With the new impeller in place I did a test on muffs. I noticed it took longer than normal to spot the telltale (approx. 5 sec) and the telltale wasn't as strong as it used to be (quite big difference). I turned off the engine since the temp gauge again (after new impeller) showed very high temperatures. I tried a three count with my fingers on the block, but let go after one and a half second.

I removed the thermostat and flushed the engine again. This time the temp gauge barely moved and the engine was almost cool to the touch (45 degrees celsius/113 degrees fahrenheit).

I tested the thermostat but since I dont have a working thermometer I cant tell if its opening at the right temperature. I have never tested a thermostat before so I dont know how much it should open either, but mine had a 3mm gap at boiling water temperature.

https://www.google.com/search?q=0394...igmgQpbATtyyM:

I have been fishing in really shallow waters (2 feet) and wonder if clay/sand can clog up the cooling system?
Does a broken thermostat show these symtoms?


best regards from scandinavia

 

[Lightwin 3]

Was the kit genuine BRP or OMC? Trust the manual for what parts are needed. I don't think there is supposed to be a gasket there.?? Non OEM kits cover many more than a specific model, IMHO.

If I remember right, you can remove the thermostat by not removing the entire water jacket plate from the head-right?

If so, I would remove that plate and look for debris.

 

[Gabbu]

Hi, I guess you are right. I will check for debris. Thx

 

[Gabbu]

UPDATE. STATUS QUO
I replaced the water pump, replaced the thermostat, started the engine (on muffs) and after 2 minutes the temperature sensor showed approximately 190 fahrenheit. Took the cover off and did a three count on the head but had to take my hand off really quickly. Didn't have a temp gun although next time I will borrow one from my neighbour. But for sure, the engine is overheating.

So I pulled the head expecting the cooling passages to be clogged, to my surprise they looked really really good. Took the exhaust manifold cover off expecting a blockage somewhere, but didn't find any. Hmmmm. I found 6 ports, going to the head, 2 close to each cylinder maybe one was clogged a bit but since the other 5 looked good I am still wondering what can be wrong.

I have done the telltale relocation to top of the exhaust block, I have changed the water pump completely, I have put in a new thermostat and I have checked all the cooling passages around the block (looking good). It doesn't add upp. Either there is a blockage or a leak. And I can't find it. The water from the telltale was really strong and almost cool to the touch.

Is this engine doomed?
Somebody please tell me where to go next. I am thinking to reassemble everything and make a final test with a temp gun, but my instinct tells me I have overlooked something.

 

[Gabbu]

I have been inspecting the water passages trying to figure out what is wrong. What baffles me is that I tried to run the engine without a thermostat and the temperature stayed around 115 fahrenheit. Installed a new thermostat and the engine overheated. I have been looking through the water diagram and comparing it with my engine. Is the majority of the cooling water passing through the gap in the exhaust cover gasket as shown in the picture? Unfortunately I couldn't add a picture , I found only one hole on top going directly to the cooling passage around the top cylinder? How else is water passing through the "wall" to the cooling passages around the cylinders?

I also found a hole underneath the bottom cylinder and wonder what kind of purpose it has.

 

[oldboat1]

There should be a bypass hole in the water pump cavity to allow cooling water circulation at start up. Perhaps that is clogged.

You cannot test water pump operation on muffs, however. A test barrel would be preferable if you add water well above the water pump location.

 

[Gabbu]

Installed the new head gasket with a torque wrench according to the manual. Ran the engine in a barrel, idled in neutral for about 10 minutes. Operating temperature stabilized at 176 fahrenheit. Did a compression test. Top cylinder 121, middle 119, down 120.

When I took the old head gasket off I recall bottom right bolt being wet, water leak? However don't you think the temperature is on the high side?

 

[oldboat1]

Did you resurface the head cover? 400 grit wet/dry sandpaper on a flat surface. Rotate the mating surface in a figure eight pattern until the shine is uniform.

 

[Gabbu]

Did you resurface the head cover? 400 grit wet/dry sandpaper on a flat surface. Rotate the mating surface in a figure eight pattern until the shine is uniform.

I did resurface the head cover with a 350 grit dry sandpaper in a figure 8 pattern, but not until the shine was uniform. I am sure I could have done it better. How small are the margins? How about the mating surface facing the head?

 

[Gabbu]

Did you resurface the head cover? 400 grit wet/dry sandpaper on a flat surface. Rotate the mating surface in a figure eight pattern until the shine is uniform.

Test run in barrel, used a heat gun for exact measurements. Top cylinder 169.3F (76,3C) middle 169 F (76,1C), down 174,4F (79,1C). During inspection I found a small water leak on the lowest part of the head gasket. I will let a machine shop resurface the head and order a new head gasket.

 

[oldboat1]

Good idea. Running hot, sounds like. (Mating surface facing the head needs to be done.)

 

[Gabbu]

Good idea. Running hot, sounds like. (Mating surface facing the head needs to be done.)

Do you need to take the powerhead off to be able to pull that off or is there some other way?

 

[oldboat1]

Just the mating surface of the cylinder head (head cover?) -- not the powerhead. I have sometimes used a block to clean up the surface on the powerhead, but main effort is the cylinder head/head cover.

 

[Gabbu]

Just the mating surface of the cylinder head (head cover?) -- not the powerhead. I have sometimes used a block to clean up the surface on the powerhead, but main effort is the cylinder head/head cover.

Thanks for the input. I will be posting my results after resurfacing and installation of the head.

 

[oldboat1]

sounds good. hope it works out.

 

[Dennischaves]

I tested my head temp last week just as a precaution and it was 138degrees on all cylinders Your definatly running hot
mine is an 84' 70hp

 

[Gabbu]

Testrun made today, in a barrel. Installed the head gasket with hylomar blue (non setting gasket and joing compound) on my newly resurfaced head. Temperatures stayed almost the same. Top 167F, middle 167F, bottom 180F. I reused my almost new head gasket, since I didn't have the patience to wait for the new one to arrive.

Took the boat out on a test run. This time we didn't bring the temp gun. 4000 rpm: exceeding 190F, 5900 rpm: 180F, idle in neutral 176F.

When I started the boat engine my temp gauge reached 180F really fast (1-2 min) and then stabilized.

I don't know what to think, really hoped it would be a big difference with the resurfaced head.

The telltale is strong indicating that the water pump is working correctly. Im quite sure the water i circulating the head. So I don't know why it's not cooling the engine enough. Can all this be explained by installing a completely new head gasket?

 

[oldboat1]

Should be testing temps on the top of the head, not the face. Testing on the face around the plugs will give you a higher reading.

 

[Gabbu]

Should be testing temps on the top of the head, not the face. Testing on the face around the plugs will give you a higher reading.

ok, I'll test the temp on top of the head. I guess no higher than 162F is ok?

 

[oldboat1]

You should be using a 140F thermostat. 160F is considered overheating.