Changed from 2 small fans to one 16 incher...

[Sledge]

....on BDR 168. Also went with a slightly larger all-aluminum radiator as the old one was leaking. Anyway, got the fan shroud from Reg, mounted the new radiator, Spal 2400-something cfm fan, and I'm happy to say, no leaks! But----

Prior to the changeout, while going down the feeway with fan(s) off, the temp would stabilize at about 87 deg C. Now it wants to run at 90 to 92 deg C. If I turn on the fan the temp goes down to 80 to 85 deg C. In stop and go traffic the temp will run about 90 to 95 with the fan on all the time.

None of the hoses are blocked or kinked, the air has been burped from the system, and yet now with a bigger fan and radiator it is running hotter. I have not made any timing changes which is 34 deg total, all in by 2500.

Do I need to cut in some flapper doors in the radiator shroud to allow more air through at speed?

I've got the fan hooked up to one of the original two 30-amp relay/circuit, with a 30 amp fuse. The Spal instructions call for a 30 amp fuse maximum. The fan draws around 22 amps when in operation. Is this system getting the necessary power to the fan? If not, what do I need to change?

Finally, I'm running a 180 thermostat. Would a 160 be better? It gets into the 90s often in summer months and occasionally into the hundreds, but the rest of the year it is mostly in the 70s.

Thanks for any and all help

[madmaxx]

Do nothing the temperatures you state are pefect. The optimium temperature for engine longevity is 100C or 212C, anything below 180F you are wearing your engine out since the pistons get hot and expand but the cylinder wall stay cool and do not expand. In my opinion you are in the sweet spot. The bs about a cooler engine develops more horsepower may apply to John Force in drag racing but for our engines you would never know or feel the difference.

[kitcarbp]

Pics would help here along with a few more details, since I dont know the shroud set-up you are now using and the rad type difference before and after. Did you change anything else, water pump or pulleys ?
Is the 16 " a puller set-up or pusher ? Were the prior twin fans puller or pusher ?
The SPAL fan if shrouded correctly should be OK. Do you know your peak HP on the engine, mild or wild ?
Based on 22 amps ,sounds about right, the rule of thumb is 10 amps per 1,000cfm with most motor/blades, and will depend on static air pressure drop, SPAL does a nice job telling you what cfms to expect from theor fans based on rad core air resisitance (pressure drop). Ensure you have 13V minimum voltage across fan connector with the fan running, if so the fan and wiring are OK. (double check and make sure fan is running the direction intended (pulll or push) . Yes air inlet flaps would help but before I see pics of the shroud cant confirm. To easily diagnose, run the set-up without the shroud but with fan mounted and if temps drop back to where they were while cruising without fan running , then shroud needs to be improved. If no change in temps is seen, the rad is not correct for your application. Speak to folks at Griffin Radiator or Ron Davis or your favorite rad supplier for advice.

The fact that your temps are higher while cruisng immediately after the rad/shroud change, points directly to the rad or shroud combo. What are the old and new rad core dimensions? Are you now using a different core style or size? More rows of tubes, different tube sizes ?

What % of core does the fan cover ?

The target temp needs to be about 190F engine out (upper hose), steady-state (fully warmed and driving highway speeds). A properly sized cooling system will have engine inlet temp of about 180F (lower hose), thats the target you should aim for. In other words the delta T should be 10F but 15F is OK also across the rad. 180F thermostat is fine as long as its functioning correctly, don't change it to a 160F.

[Sledge]

The radiator was one that Reg Dodd recommended, a '96 M3 radiator, which is a little longer (about an inch) than the standard BMW 325 radiator. The shroud is a stock BDR 16" fan shroud, also recommended by Reg. I don't have photos yet, I'll try to get some. And I'll check the voltage at the fan as recommended. Since my old radiator leaked a bit, I think this one holds better pressure, and that may have an effect on the temps I'm seeing. As long as they don't go much above 95 I'll be ok with it, I'm just not sure what the first hot day is going to bring.

It is a puller fan and it is turning in the correct direction.

So a 30 amp fuse should work okay for this install, as long as there are 13 volts at the motor when the fan is on?

Thanks!