Normal operation temp on RB25DET...

[USRB25S13]

I have ran into a runing hot problem on my 240sx with an RB25 swap.

It used to run around 80-85C on my PFC while driving around and would climb when I came to a stop since I don't have a larger enough fan.

2 weeks ago I mounted my FMIC in my car and now the temp will stay in the mid to high 90's (94-99) while moving on the highway. The only way to keep the temp in the low 90's is to keep my heat on full blast. I was then talking to a friend about running the car that hot and he didn't think it was a problem unless it started going over 104+C. I know some cars don't turn there cooling fans untill 220-230F.

So what does your car run at?

[ed]

mine never gets over 90.

Have you tried putting in a lower thermostat?

[Sydneykid]

Anything over 90 degrees is costing power, 85 is the best running temp to target. I suggest a larger radiator is a worthwhile investment. This is standard stuff for an RB in an S chassis, there is simply not enough airflow (particularly outwards).

[ed]

SK, is it bad if the water temp is too low? say 70 for example.

[USRB25S13]

What temp should be considered dangerous to the engine?

[Jimbo2000]

yeah mine sits between 78-81 always, unless aircon is on

[GunMetalR33]

Mine averages 81 but it does go as high as 86 or so...

[PHaT MR30]

Yeh the std radiator is crap, ive got a custom alloy radiator with twin 12" Davies Craig thermo's... round town its between 74-84 degree's, on the highway it was getting as low as 69 which i may have to make some changes to. having trouble with the switching on the microtech.

[USRB25S13]

I don't know if a larger radiator will help me since my problem seems to be a lack of airflow to my radiator. Before the FMIC was put in front the car would run a sable 78-83 highway and 85-95 light to light. Now the temp will not go below 91 once on the highway and that is with the heat on. It is summer now but starting to cool off. To get more airflow I was thinking of putting some vents in the front nose of my car. I am running 90% water/10% coolent with some water wetter.

[NewKleer]

where is water temp measured from? is it that drain plug thing in the bottom of the radiator (mine has the wires chopped off) or is it measured from the thermostat in the housign where the coolant comes from engine back to radiator?

ive just put a replacement triple core radiator in my rb25 sil, still need to mount a thermo fan. temps used to be up to nearly the 3rd notch on the temp gauge. last radiator (r32) developed a leak hence the replacement.

[Sydneykid]

SK, is it bad if the water temp is too low? say 70 for example.

Not bad as in damage, but bad is costs power. Around 85 degrees has been proven to be the best for both. This is water temp of course and from only one sampling point on the engine. Oil temperature, exhaust valve temp, turbo temp (exhauts gas) etc are all important. But the rule of thumb is 85 degrees for the running water temp.

Hope that helps

[LBR33]

FMIC reduces the airflow to the radiato. My advice would be to upgrade your radiator when you fit a FMIC.

[SLY33]

I don't know if a larger radiator will help me since my problem seems to be a lack of airflow to my radiator.

if the amount of air you currently get thru your stock radiator removes a certain amount of heat from the coolant, a larger radiator will remove more heat with the same air, as its more efficient (due to larger surface area)

[Cubes]

The straw that broke the camels back.

The clutch fan could be on its way out. the fmic reducing airflow could have been the last straw.

I run a bar and plate 100mm thick fmic, I used to have overheating problems with constant over 90degree temps so I slapped a pair of 12" thermo's on without a shroud (big mistake).

Temps came down below 90degree's but the overheating problem showed its ugly head on 35+degree days with the A/C and began spitting water out the overflow (water boiling 110degree's).

Out came the thermo's and in goes a new clutch fan and shroud.

The amount of air the std clutch fan now moves when engaged shits all over the 2 x 12" thermo's and a 16" thermo I've seen.

Temps are now perfect and never get over 90degree's.

So.. Check the clutch fan. Make sure you can hear it loudly for around 10secs first thing in the morning when you start the car. If not its shat its self.

[blind_elk]

You could also try some vents in the bonnet to reduce the air pressure inside the engine bay.

Have a look at www.autospeed.com for a recent series of articles on sighting air vents and undertrays.

[GTRgeoff]

That might help but the problem with RB's in sylvias and 180's is common. A larger radiator is a good choice as it adds thermal mass to absorb heat spikes when the car is stationary. I recall the RB25 radiator does not fit with an RB20 as it may have been too tall.

[NewKleer]

thats right, i recently bought an r33 radiator on the assumption that it would fit, but its about 2 inches too tall.

the only problem with a thicker radiator is it means even less room for thermo fans....if u want to keep the air con that is

[discopotato03]

I had similar temperature problems with a Bluebird 910 running an FJ20ET . No aftermarket multi core copper/brass radiator worked nor did cooler thermostats . It also had a large Plasma Man intercooler completly shrouding it . The ultimate fix was a Koyo replacment R32 GTR radiator , the core was about 20mm thick and was a single row matrix . The fans I used were DR30 twin electric in their native steel shroud . Problem solved . I cannot sing enough praise for alloy core radiators , they weigh about a quarter of what the old dinosaurs do and are way ahead in heat transfer capacity . It was explained to me that with alloy cores the surface area of the fins is greater while air flow through them is less restrictive .

With the Bluebird it was not possible to use an engine driven fan because the FJ20 is so long (Thick walled 89mm bore block with two twin row staggered chains and the water pump ahead of all this) . The way I see it the cooling system needs to have lots of capacity preferably force fed by an engine driven fan with the temperature regulated by the thermostat . I've seen plenty of people remove the "clutch fan" to fit electric ones to save horse power . They create cooling problems and save about three foot grams of torque .

More specific to the RB20/S13 JMS also found cooling issues with their S13 . The fix was to refit a standard style air dam and make a vent in the bonnet to let some of the post radiator air out . They changed from I think an S13 SR20DET rad to one of the Skyline ones . As SK said its getting the post rad air to exit the engine bay that will be the greatest challenge . If all else fails an oil cooler could help if it gets decent air flow and does not vent into the engine bay .

Chow A .

[PHaT MR30]

Due to the lack of engine bay space my thermo's are mounted in front of the radiator? i question the wiring as to the direction of flow but i could be wrong. keeps it cool and thats all that matters.

FMIC might be what the doctor ordered in relation to the over cooling problem.

[ed]

Not bad as in damage, but bad is costs power.  Around 85 degrees has been proven to be the best for both.  This is water temp of course and from only one sampling point on the engine.  Oil temperature, exhaust valve temp, turbo temp (exhauts gas) etc are all important.  But the rule of thumb is 85 degrees for the running water temp.

Hope that helps

Thanks.

Has helped alot.

Another question.

Which would be more accurate spot to measure the water temp?

The factory location or the usual aftermarket location of the top radiator hose?

Ed