Overheating on motorway/fast roads

[alexanderfoti]

Hi all

Following on from my further refining of Tim's old Superdream 850, I am now tackling the cooling system.

I have replaced the old gauge with a digital version of the same and went out for a ride today:

It hovers around 70-75 on 40mph roads. I can also feel that the thermostat is working correctly as when it gets to around 82, my seat gets warm.

As soon as you get it on a motorway or fast road (60+) the needle just keeps rising.



The red X is an Aux cooler plumbed into the header tank line (before thermostat)

The blue X is the main radiator. It has 2 large fans running constantly. My first thoughts where airflow. So I removed both the red side panels. No change.

In fact the reading went up to 104 and I had to slow down to 50 to get it come back down again.

I am stuck a bit now. I can only assume the 12v water pump doesn't flow quick enough. Maybe replacing it with a more powerful version will help?

[BertTrack]

I'd look into the flow first. The placement of the radiator would require a higher through put than in front of the engine as the coolest it will ever get behind is around about the engine air temp around the block?

Also there should be a good blast of hot air from those fans when it's that hot. Maybe the fans aren't sucking enough? How well enclosed are they?

[alexanderfoti]

Possibly, although when the fans are running at a standstill, they are pumping a large amount of hot air out, which I why I think the placement isn't that bad and the flow isn't that bad too.

Tim has the same setup with the 482, granted he has a slightly smaller engine, but also a turbo, so the cooling load is similar.

To put the radiator at the front, it will require one half the size as there just isn't the space at the front

[Eddy Wane]

Reading other forums re Kubota engines. The consensus seems to be that 82 deg C is the norm. That also appears to be on the cool side according to forum members although the kit is mainly tractors and ride on mowers. You might not need to do much to keep the temperature lower than that on the bike. Perhaps an air scoop may help.

[alexanderfoti]

Reading other forums re Kubota engines. The consensus seems to be that 82 deg C is the norm. That also appears to be on the cool side according to forum members although the kit is mainly tractors and ride on mowers. You might not need to do much to keep the temperature lower than that on the bike. Perhaps an air scoop may help.

Agreed, the stat starts to open at 82, and is fully open by 92 I think. However, I am hitting 104 Deg C on fast roads.

[albertaphil]

Reading other forums re Kubota engines. The consensus seems to be that 82 deg C is the norm. That also appears to be on the cool side according to forum members although the kit is mainly tractors and ride on mowers. You might not need to do much to keep the temperature lower than that on the bike. Perhaps an air scoop may help.

Agreed, the stat starts to open at 82, and is fully open by 92 I think. However, I am hitting 104 Deg C on fast roads.

If the engine is only running at 70 degrees under low power I would think your thermostat may be stuck partly open. Does the engine take a long time to warm up? Maybe the thermostat isn't opening or closing all the way.

It seems to me with a properly functioning thermostat that once the engine warms up it should maintain temperature even under light load.

[Eddy Wane]

Alex.
Reading further on the web. Average engine temperatures are between 185-212F, changing the radiator cap pressure from the "standard" 1.1 bar to 1.3 bar raises the boiling point of the coolant by around 8 F. Antifreeze mix of 50/50 is also recommended as the correct mix. So if your Dream is hitting 102 C that could be normal for that engine. Even my Deauville temp rockets up when stationary and sets the electric fan off.
Eddy.

[alexanderfoti]

Reading other forums re Kubota engines. The consensus seems to be that 82 deg C is the norm. That also appears to be on the cool side according to forum members although the kit is mainly tractors and ride on mowers. You might not need to do much to keep the temperature lower than that on the bike. Perhaps an air scoop may help.

Agreed, the stat starts to open at 82, and is fully open by 92 I think. However, I am hitting 104 Deg C on fast roads.

If the engine is only running at 70 degrees under low power I would think your thermostat may be stuck partly open. Does the engine take a long time to warm up? Maybe the thermostat isn't opening or closing all the way.

It seems to me with a properly functioning thermostat that once the engine warms up it should maintain temperature even under light load.

Thermostat is working ok, I can feel the hot air from the rad at 82 deg C. the over cooling is from the front cooling fins (Red X) as they are wired before the stat. I will be removing this loop.

[alexanderfoti]

Alex.
Reading further on the web. Average engine temperatures are between 185-212F, changing the radiator cap pressure from the "standard" 1.1 bar to 1.3 bar raises the boiling point of the coolant by around 8 F. Antifreeze mix of 50/50 is also recommended as the correct mix. So if your Dream is hitting 102 C that could be normal for that engine. Even my Deauville temp rockets up when stationary and sets the electric fan off.
Eddy.

I would be happy, except I get 104 when at 70MPH. If I keep at that speed (fuel demand) the temp just goes up and up and up.

[Diesel Dave]

You need a bigger radiator.......

Otherwise as soon as you encounter high ambient temperatures it's gonna cook the motor.

[alexanderfoti]

The current rad occupies all of the space under the tank.

What im going to do is remove the aux cooler at the front, and connect a larger actual radiator in series with the other radiator and take it from there.

[alexanderfoti]

OK, busy today.

New radiator arrived, and whilst its a tight fit, it fits. Its a shame the hoses couldn't exit out of the back, but there just wasn't enough space. The rad was only £20 brand new so cant complain.

Its thicker and wider than the one behind the engine, but not taller.





The original front cooler removed, and this one is wired in series with the other large rad at the back.

Went for a test ride today, Similar weather, exactly the same road, Temp gauge sat at 80.

I'm now on the other end of the scale, the thermostat is barely opening and the engine is nice and cool. On super hot days there should be more than enough capacity.

I'm thinking, I wonder if it would be possible to remove the rear radiator now? It is rather crampt with the coolant pipes (as you can see!)

[Tetronator]

Looks like you've got a kink in the coolant hose on the left side, you might want to address that.

Looking good tough.

[alexanderfoti]

Yes indeed, I need a prebent 90 degree hose, that one wont bend in the space I need it to.

[coachgeo]

Maybe a radiator shop or anyone that can weld aluminum can turn the pipe on that new radiator in a different direction? Say straight up..... or ???. You can test not needing the back radiator by just bypassing with temporary plumbing. If don't need it remove it. If it is iffy.... put a protective cover over the front one that also blocks off part of the radiator. Maybe have removable plates on front of it so you can very how much air it receives.

[sbrumby]

Attach rad to copper pipe with short rubber pipe , then you can use soldered bends either 90 or 45, My LE Velocette has 20 jubilee clips joining all the pipework together.

[alexanderfoti]

I like the copper pipe idea. Maybe spray it black so it doesn't stand out so much.

Yes indeed, Coach, just need to block the rear rad now.

I was out today, blistering heat all through town, highest I saw was 97deg ,BUT I have the fans turned off completely, as soon as I started moving it dropped down pretty quickly.

It would be nice to remove the rear, as its pretty crampt back there.

[coachgeo]

My understanding is copper in a working environment is prone to vibration stress and cracks. Don't quote me but seems I've heard about this a bit from those who were converting diesels to Veg oil fuels. Recommendation was to mount it with rubber hose on both sides and NOT to braze solder to solid objects. Also not always easy to seal rubber hose to it either. For that you might have to find a way to put a flare in it or solder/braze in hose barb. Then there is the dissimilar metal issues which I believe is why most machines no longer use brass or copper anything that come in contact with coolant.

[sbrumby]

Believe what you want but old rads are brass and are soldered together.

[coachgeo]

Believe what you want but old rads are brass and are soldered together.

Good point but then again..... well?, yes and no? They are mounted within a frame which is not brass and may well help reduce this vibration issue. All is mounted to body that has some anti vibration qualities too..... and all coolant lines from engine and trans cooler too I think are rubber at least at one connection. Beside...... we got to admit.... our diesels projects vibrate a shiat load more than the average.

[sbrumby]

People might actually believe the things you say if you had actually made a bike.

[pietenpol2002]

I've just gone to several local auto parts stores where I was given permmission to rummage through their reserves of pre-bent hoses until I find what I want. They've got every conceivable bend you could ever want.

[alexanderfoti]

I ended up doing just that, a mates garage and went through their spare hose box

Did lots of town riding in this very hot weather. Fans manually set to full on the way to destination.

Never went above 78 degrees c.

On the way back, turned the fans off completely. Very heavy traffic, sat at 81 degrees most of the time. Rose in heavy traffic to 93-95 max (with no fans!)

I would say it's solved! Will be doing fast Road riding tomorrow so will see what happens then.