1988 40hp VRO Overheating while Trolling Fine while going Fast

[Sausage_lx]

Hey Guys, I've been reading your forums for a while now and your knowledge is amazing

I am having a crazy problem. My Johnson 40HP VRO (VRO Removed and running 50:1 pre mix) is over heating ONLY when trolling. I can blast around the lake for hours no problems at all Troll around to try and catch a fish after 30min it will overheat

After reading on here all about how to trouble shoot wiring faults. I took it out on the lake, went for a 15min full speed runto warm her up to behind a few islands. Checked the block tempurature 93f on the top and 90f on the head with a laser temp meter. Then I just clicked it in gear and trolled forward slowly for 35min then the overheat alarm went off. Temp on the top was 211f and the heat was 209f. So it had definatly overheated. Start it up again go full speed again 30secs later alarm went off, went around the island took about 4mins and took tempurates again top was 120f and head was 107f.

The engine always has a nice tell tail. And I had the waterpump impeller changed last weekend after I discovered this problem. And I just blew compressed air thru the rubber line from the telltail to the block and it seems to be fine

Anyone have any ideas??? Does this engine have a thermostat that might be not working and maybe being forced open at high pressure running at full speed????

Thanks in advance guys

 

[milliesdad]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

It has thermostats and water deflecters.

Before diving into it, get a manual.

I've got the 50HP version and have a working VRO.Why did you remove it?

 

[Sausage_lx]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

VRO was removed before I bought it

 

[KCKracker]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

i had that issue 2x, both times it was tstat, i could haul butt , but, if we went slow it screamed hot fast.

 

[Sausage_lx]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

Can you remember how hard it was to change the Tstat?????

 

[KCKracker]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

Can you remember how hard it was to change the Tstat?????

very easy

 

[Sausage_lx]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

Hey Guys, I know it's been a while since I posted but I am still having the overheating while trolling problems, and I'm hoping to get it sorted over the winter

Towards the end of the season I had the Thermostat changed. And it made no difference, the motor overheating while trolling.

Here is a summary of what going on - I have a Johnson 40HP VRO (VRO Removed and running 50:1 pre mix) The Motor overheats ONLY when trolling. I can blast around the lake for hours no problems at all, Troll around to try and catch a fish after 30min it will overheat.

I took it out on the lake, went for a 15min full speed run to warm her up to behind a few islands. Checked the block tempurature 93f on the top and 90f on the head with a laser temp meter. Then I just clicked it in gear and trolled forward slowly for 35min then the overheat alarm went off. Temp on the top was 211f and the heat was 209f. So it had definatly overheated. Start it up again go full speed again 30secs later alarm went off, went around the island took about 4mins and took tempurates again top was 120f and head was 107f. So it is definalty overheating and not a wiring problem

I have had the water pump impellar changed, and I have had the Thermostat changed. No repairs have made any difference so far

The Unit always has a nice flowing tell tail.

Anybody have any theories why my engine is still overheating????

 

[oldcatamount]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

Sounds like somethings leaking. There's a rubber grommet on top of the impeller housing that receives the copper tubing coming down from the powerhead. It's possible that grommet is leaking water. Since the volume of water increases with rpm, the motor is receiveing adequate cooling at higher rpm and not at low speed. Take the lower unit off and have a look at the grommet. Problems like that are common when re-installing the lower unit and not making sure the tubing is seated in that grommet.

 

[kbait]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

+1 on the grommet. Check it for rips, or perhaps it was folded over upon last LU install.. Also check water inlets for partial blockage.

 

[phillnjack2]

Re: 1988 40hp VRO Overheating while Trolling Fine while going Fast

Yes i agree on the rubber from the copper tube to impellor housing.
best to get a new one ready and replace it anyway.
do not lubricate it to put it on niether, or it could get pushed up too far and the same thing will happen.
Now if you clean the copper pipe just above where the rubber goes to, you can put something like a piece
of waterproof tape there to help stop the rubber from climbing up to high when you put it back together.

If its not this, then you need a new waterpump housing and bottom impellor plate, and make sure if yours
has the o-ring on the impellor housing or not (check manual for your engine) !!!!
And have you had a bad impellor recently ? could be a broken piece is stuck up in the waterways and not
letting enough water get around the block . ?

good luck do put a new piece of pipe on the impellor to copper pipe joint.

and put plenty of washing up liquid on the impellor so you dont rip it up when you first start the engine.


phill...........