Well guys,
All went well with my suby conversion, kombi ran great, no cooling issues until I hooked my little caravan on! I can tow it around town at 60ks all day and have no issues but once on the highway at 80-90 ks the temp climbs up, even when the fans cut in it still keeps creeping up. Pulled the thermostat, all good, and pretty sure most of the airs out.
I'm wondering if the airs not pushing down thru the radiators because I don't have negative air pressure in the engine bay?
Also wondering if a small amount of air trapped in the very top of the radiator is going to make a difference, the only way I can see to fix that is to put a bleeder in the top of each radiator.
Just seems strange it's overheating on the highway and not around town.
Appreciate any feedback

Cheers Johno

its could be the very thing you are towing disrupting the vacuum behind the kombi that draws the air through the system, plus a combo of extra load not helping either.

caravan is a massive aero brake.


my suggestion.

see my suggestion above ^

Well had a play around this morning and I'm pretty convinced the cooling problem is due to hot air not being able to escape the engine bay. I took it for a drive with the engine lid open and it was much better,not perfect, but better. The caravans not helping with the airflow, without it there's no drama at all. I think what I'll do when I get home is extend the firewall down, bring it in line with the bottom of the crossmember and try and create some negative air pressure in the engine bay. The engine bays just too open with the suby engine, too much air is flowing in and stopping the air getting pushed thru my radiators from the side vents.
If that fails I'll make a mesh engine lid,
If that fails I'll put a bloody radiator up front,
If that fails I'll sell the caravan and put the original engine back in,

Anyway packed up the family opened the engine lid, connect the caravan and we're away on our old bar pilgrimage.
Nrma premium cares all paid up, let's see if we get further than last year.

Lot of factors involved with cooling systems. Our bus has the radiator underneath between the rails in the middle of the bus. It works well in town and 100kph on the highway. However at 110kph it gets warmer, and 120 kph warmer again. I have looked and tested different air temperature days, and different speeds over the last 9 years. I can drive on a 45 degree day no problem around town, and at 90kph, the temp never gets over 100, and the fan come on at 95.

So the fan can come on at the following speeds full time. Not ideal.

At 100 kph, the temp goes up to about 90 on a 35 degree day, and up to 105 on a 45 degree day
At 110 kph, the temp goes up to about 100 on a 35 degree day, and up to 115 on a 45 degree day
At 120 kph, the temp goes up to about 100 on a 30 degree day, and up to 110 on a 35 degree day

The extra speed, means more horsepower required to be used to move the brick through the air. Horsepower increase always means heat increase. The other side effect is that higher speed means lower air pressure under the bus, which contributes to less cooling, as lower air pressure through a radiator will cool less.

The original VW air cooled system had higher air pressure at the air intake vents, and lower air pressure under the vehicle, so the flow would want to travel quickly from the top of the engine to under the engine. This is why the original tinware and engine bay seal were important, as the air could only travel through the oil cooler and over the barrel fins.

The same principal is used with front radiator cars, as the air is forced at high pressure into the front grille of the vehicle, and the low pressure under the engine bay will accept it

100 is fine, it is a pressure system. 110 is your limit, as the safety is being removed. The 13 psi cap will pop at about 116 degrees, and with a 15 psi cap it can be raised to about 120 degrees.

You don't hurt an engine running at 110 degrees, you are just getting closer to your margin of safety from popping the cap. In fact hotter running engines run more efficiently. Fuel economy and engine life are better at hotter temperature. The cap will pop to release the pressure. I have had up to about 115 degrees, and the cap has never popped.

Once the cap pops, you have lost water, pressure, and the cooling system needs a rest and refill before continuing.

there is a threshold though when engine efficiency drops as well as engine life. depends on the engine though. Most water cooled engines this is about 105ish.

Depends on the material of the engine and machine tolerances mostly. The worry with water cooled alloy engines is the large heat capacity of aluminum. Much greater than the old days of cast iron.

So a 5ºC increase in temps equates to an enormous amount of stored energy you need to get rid of, and just makes it harder once its hot. You got issues of heat soak as well with water cooled alloy engines.

I would be worried over 100 and trying to keep under 105 max imho.

I agree. 100 is the safe limit that allows for safety margin, and still well within popping the cap. 90 is probably the nicest place to be.

Cheers guys, feeling a bit more confident knowing that, like I said I was shitting myself at 95 degrees!!
Johno

Just had a look to see what my cap is, it's 17psi, that's what came with the ba falcon header tank I'm using. Doesn't hurt to be running that psi does it? The system seems to run fine, actually I thought the hoses would have been really hard to squeeze but at operating temp theirs a fair bit of pressure but not massive, I reckon that might be because of the long length of hose I'm using.
Anyway just hooking up the van and try another drive. Feeling more confident today,
Thanks Johno

if I had it my way, peaking at 100 would be just fine, normal range between 90 and 95.


I wouldn't use a falcon header tank, those are prone to blowing open at the drop of a hat, normally around the bottom outlet.

You are better of getting a alloy fabricated header tank or choose an OEM one thats not known for breaking.

ARE make top quality ones and they do a falcon one if you just want the same.

Actually have a chat to the guys at ARE, they by far the best experts on radiators and cooling system designs. They were really helpful with my projects and advice.

ARE= Aluminium radiators & engineering.

Subaru temp gauges like most Japanese cars have a static zone between 80 and 110 where they don't move and just sit in the middle.

It has to get above 110 before the needle starts moving up to hot so that should tell you no need to panic too much if its under 110.

Joel- thanks that's good to know, I've been between 102-104 a couple of times today on some of those long hill on the Newcastle freeway, but nothing more. Just learning to putt along at 85-90 ks, if I could get the cooling right it would cruise along with the caravan at100.

Vlad- good idea re the alloy tank, I will get one, I just grabbed a plastic one to basically see how the whole thing would work, but I'll go to an alloy one now that I know the systems right.

Cheers Johno

you could look at revising the radiators, get some customs ones made, larger(thicker) core, better shrouds, inlet/outlet on the same side of the radiator as that is more efficient at exchanging heat.

There is different types of tubes and fins available for the cores, much better than OEM and cheap alloy ones made in china.

Just looking at your ones, the end tanks (headers) have their in/outlets in really crappy spots, unable to maximize heat transfer due to poor flow path through the core. Not to mention poor self air bleeding also attributed to the in/outlet positions


There is heaps that can be improved with just the radiators alone there.

Worth having an expert design and build your radiators to suit the application.

make sure it works on a very hot day 40deg and she sweet .

fans don't come at speed because doing 100ks you have 100k wind going through your radiator .

Just read through this thread and a couple of things occurred to me...

1. Imagine a EJ22 powered liberty loaded up to the roof (2500+kg) and towing a caravan in warm weather. That's maximum load for that engine.
2. The thing about the effectiveness of cooling systems is, you find out the truth, right at the limit.
3. Rear mount radiators setups are exceedingly hard to get right. Karmann141 is one of the very few who've got it right.

What to do?

Personally, I'd go with what Peter (helbus) has done and put it under the bus or front mount it. What you want is direct, laminar airflow.

You could spend 100s of hours getting pressure areas right via ducting and the like, but a really hot day with a crosswind would send it all to hell anyway. I had that exact experience. Front mounting my radiator meant I almost never needed the fan again. Heck, even the pipes sending the water forward helped cool it more.

P.s. put the thermostat back in. With it out it shortens engine life considerably by taking ages to warm up properly. Then when the engine gets hot, the water rushes through the radiators faster than they can cool it. The only mod I did to mine was pulling the flipper valve out to aid bleeding.

Quote:

Originally posted by ian.mezz Quote: Originally posted by karmann141 Quote: Originally posted by ian.mezz fans don't come at speed because doing 100ks you have 100k wind going through your radiator . Thats not correct - at 100k/hr if the pressure at the front of the radiator was equal to the pressure at the rear of the radiator (100k/hr under the vehicle) you would have no flow through it - regardless of how fast you drove. There must be a pressure differential because it works - yours just needs tweaking - part of the fine tuning/learning experience. Your flow direction is fine - firstly need to get all air out of the system - I conveniently have an air bleed at the top of each radiator. In winter if not towing I removed the Earz and blocked off the number plate standoff as it wouldn't get over 80deg C. Went on a 1200km camping trip in mid Qld summer in mid thirties with 4 people, full load of camping gear and trailer and fans would only come on for 30 secs in traffic or on a long climb. Will fine tune it some more with under body aero. No I havent had vapour lock and my pump is in much the same location as yours but I did have a lift pump and surge tank which I have since removed - haven't had a Summer without it yet. Cheers I said that he would have trouble . yer sure in regard to air speed I was assuming that we all knew the pressure thing , air flow ,open a quarter window on a bug and feel the air pump in and his got heaps wrong with his set up, he even has the fans blowing hot air at each other

Good onya vlad - I think he is being serious!!

He maybe onto something, what about I reverse the fans so they're blowing back out the side vents and put a set of ears on the vents but face them backwards!😋

won't work.

Won't work x 2

There is nothing much wrong with your cooling system as it works - its just not coping with the additional load of towing.
Hence your system needs to be as efficient as possible and you need to address the issues previuosly mentioned - air in system etc.

It would be a retrograde step in my opinion to hang a fugly radiator out the front or underneath where it is prone to damage.

Just have a closer look at any bus or coach - engine and radiator in the back - they can't all be wrong.

Was just joking fellas

haha got us good.

yeah your system is 90% there, just need a little refining.