I’m currently running a T25 that’s oil cooled only. My understanding is that the oil is the main coolant during operation and that the water cooling is primarily there to prevent heat soak after shutting down. If that’s the case do I really need to connect the water side of things up if I’m running a turbo timer and allowing it to cool down slowly? Also, if I do need to connect the water up, anyone know where I can get the hoses and joints manufactured?
Many thanks.
I’d not bother with the water cooling (none on my Greddy turbo) and I’d not bother with the turbo timer either. Leaving the engine running at idle while the car isn’t moving actually makes it hotter under the bonnet than turning it off. While the cooling oil flow does stop when the engine is turned off, so does the 900 degree gas flow that heats it.
Almost any car factor should be able to make or source water pipes, if you want to run with the water cooling. Bare in mind that unless you fit an electric auxilary water pump to work when the engine is off all the water in the turbo will do is get very, very hot.
I would run the water cooling, and do so on mine. You should be able to get the fittings from a local turbo reconditioning company, and use heater hose from any motor factor to pipe it - just divirt the the small pipe on the thermostat to run thro’ the turbo
Keep running the timer, its the heat soak when you switch it off from red hot that does the damage
Thanks guys. Doesn’t sound like a difficult job. Trouble is I’m easily led 
, and it’s 1-1 in the yea/nay stakes. I can see the logic for both sides of the argument, but I suppose adding cooling is the more conservative approach and can do no harm…?
You realise that none of the OEMs who engineer their cars to last a minimum of 100,000 miles use anything like a turbo timer? It just isn’t needed for durability. They do a test called a thermal cycle, where they run the engine under load on a dyno at maximum power (to get everything cherry red) then turn off the fuel and spark and run the engine at idle speeds to pump cold air through the engine to rapidly cool it - much more extreme than any running conditions you’ll find in the real world. They repeat this cycle for hundreds of hours on tens of engines, during which they must have zero failures.
Turbo timers aren’t used in racing either. They are just an invention of the “tuning” industry.
I’ve done a thermal survey of my turbo’d MX5. If you start a turbo’d engine from cold and just leave it idling you will get surface temperatures of well over 350 degrees at the turbo. Idling an engine creates heat. Look at the thermal inertia of the turbo, look at the cooling curve between 900 to ambient compared to 900 to 350. There are no benefits to fitting these devices.
No they don’t fit as turbo timer as standard, but they do tell drivers tt idle the engine for a minute before turning off. (Evo)
Even when I’m on a track it takes longer than a minute at less than 2,000rpm to park in the pits.
I can’t imagine any circumstances when I would be turning off an engine while running it at 7,000 under load. It’s just not needed. Unless you do a rolling burnout in to your driveway.
Edit to add - you say “(Evo)”, is that a recommendation from the handbook of a Mitsubishi Evo, or something a journalist wrote in a magazine?
Mitsi handbook
Ta. Just checking now with a chap writing the handbook for a turbo’d car for another manufacturer.
Edit: Hmm, no need on that engine because it has an electric water pump :shrug:
“After driving at freeway speeds or up a long hill, idle the engine at least 30 seconds to cool the turbo. …”
source …Mazda MX-5 Owner’s manual.
Turning off at the motorway (sorry about the rude “m” word) services would be an obvious scenario (or racing home from work on a promise)! 
Mazda didn’t fit a boost gauge either but I wouldn’t be without it.
Having said that, a turbo timer would turn me off pretty quickly.
But when you turn off the motorway you have to lift off the throttle to slow down, brake down the slip road, trundle through the car park, find a space and park - 30 seconds cooling down time is built in to the journey, surely?
I’ve always heeded the advice given to me when building a rally engine for my old subaru and that was water cooling is ineffective on a turbo as the temperatures they run at just super heats the water returning to the engine, it’s super heated steam. and if the engine is turned off there is no water flow and the water helps hold the temperature in the turbo. Oil is the best way I’ve ever heard of cooling a turbo as it doesn’t boil and can deal with removing the high temps seen in a turbo.
Advice I’ve received that I abide by now and have had no problems since.
Cheers Steve
I haven’t posted here for quite a while, but I think this one’s important enough to break the habit.
There is a difference between an oil colled and a water/oil colled turbo, both internally and with respect to oil flow.
An oil cooled turbo like the Greddy is designed to flow quite a lot of oil, in order to provide cooling as well as lubrication.
Water and oil cooled turbos, like the Garrett t25 have different internal construction, with the oil only passing the bearing areas,
and the water passages providing most of the cooling. In addition the amount of oil flowing is expected to be restricted to minimize the
risk of the oil getting past the shaft seals. This is even more important where ball bearing turbos are used; Garrett recommend a 1.5mm orifice
in the oil feed line for sleeve bearing turbos, and 1.0mm for the ball bearing series.
On my old MX5 I had a separate water cooling circuit, with a pump that ran when the ignition was on, and for 5 minutes after it was switched off,
this was on a Garrett GT28 turbo.
To maximize the life expectancy of the turbo I would ALWAYS go along with the manufacturers recommendation, and if they fit water cooling to their
turbo it is there for a reason!
,
If your turbo has ports for water hoses to connect up to, then connect them. The designers of the turbo must have put them there for a reason after all.
Just fitted a T28 to my 1.6, water cooled all the way as someone with the knowledge pointed out, the T25 and T28 are primarily water cooled by manufacture, not all turbos are the same, if its fitted use it.Also, I notice that the water pickup is from the bottom of the thermostat, we used the outer heater matrix hose, works perfectly and not too difficult to source a nicely fitting pipe, as for fixings, jubilee clips.
As for turbo timers, the theory is right but I have never seen them in motorsport, mainly seen them on Jap import Turbo diesel jeeps, nuff said!!!