slight cooling issues and how to tell if fan clutch is bad?

ok my car seems to run cool at 195ish, i currently have a 195 tstat installed.

i do have a mech gauge so what i am seeing is accurate.

cooling system is a stock replacement pump, replacement fan and clutch, OE shroud and stock radiator, AFAIK its the FACTORY radiator. never has given me any issues so i have kept running it.

car will get up to temp and run pretty cool at 195, cruising down the road or highway it cools fine, when i start slowing down and start hitting stop and go traffic, the temp gauge rises slowly, will get 210 or better, i think it would get hotter but i havent been pinned in one place for too long.

i know 210 isnt hot but i think a good cooling system should keep the engine cool all the time. i also notice after a good WOT pass rowing the gears i notice a temp increase shortly after letting off the throttle.

i hate to dish out the cash for an aftermarket radiator is that isnt the sole problem.
is there a surefire way to tell if the fan clutch is bad? AFAIK the clutch should lock up once its gets hot or something and become stiff and not be independant of the clutch.

well mine when i run the car for a while, i can shut her off and get out of the car and can still turn the fan with my hands, there may be a slight resistance, but honestly it feels just like it does with the car cool.

so what exactly locks up the fan clutch, heat??

the fan i have isnt that old, maybe 1.5 years and i have noticed around where the fins meet the hub the plastic is cracking real bad. is this just parts from the store or am i turning too much rpm for the fan or too fast etc??

have always had good luck with stock clutch and fans so if they will cool my combo i would like to keep using them, even if i have to buy new ones.
maybe i just need a good radiator, but it sure seems like a fan issue since it cools great with enough airflow (going down the road) but will get warmer with less airflow like slow speeds and idling.

any input?

drove the car some earlier, like i said it cools very well as long as your up to speed to get good airflow. but once you start driving under 35 in town and stop and go driving it doesnt take long to get warmer, highest i have seen it at is 210 but it seemed like it would have kept going up if i kept at slower speeds.

got home from driving, everything was up to temp and all in order, popped the hood shortly after getting home i felt my brothers mustang's fan, his car is bone stock and has the same fan setup as me. it had pretty much no resistance in turning it.

went over to my car, while you can still turn easily by hand there is a considerable difference, alot more resistance.

i know my brothers car cools really good, i guess i can just try his fan out and note any changes, i hate to just dish out the cash for a new clutch, they are rather pricey, i would have to know for sure.

it doesnt freely spin like a pinwheel at all.

so if the fan clutch isnt the culprit what should i look to next, the radiator?

the radiator looks like a bone stock factory one, some of the fins are smashed and what would the deposiits looks like on the ports? never payed attention to any that did.

the crank pulley on my 1 pc blower pulley is a 4 inch underdrive. i was using the stock crank pulley but this pulley came with the under drive. the WP and alt pulleys are stock size. i used to run underdrives and never had cooling problems.

drove the car a few mins ago with a hawks eye on the temp gauge and i am really leaning towards the radiator.

started it up, immediatly start driving it around, car got up to temp normally and i was on the highway as it warmed up, so the car ran at 195, stopped at my house and picked up my laptop to do some logging. water had a few mins to get warm just sitting i the motor while i went into the house. started the car again and headed towards the higway again, this time it started running 200 ish, got to the highway, was up to speed, car didnt get back to 195, i slowed down and did a few WOT gear rows up to the top of 4th while i logged it.

after the first WOT run it got to like 205 as soon as i was done with the WOT pass.
after the 2nd it was reading 210-212 as soon as i let off the gas it seemed like. was on the highway so i was going 65 as soon as i stopped WOT. so the car should have cooled down. well it did but too forever.

i have had some fan issues before with some elec fans and it wouldnt cool in town, but as soon i got on the highway it would cool down QUICK, like less than a min it would be totally cooled off with the good airflow on the highway.

today it wouldnt ever come back down to 195. started at like 212 and after almost 10 mins on the highway it only came down to like 200-203 or something.

before i drove the car today i popped the cap off the radiator and it does look like there is some sort of brown build up around the outlets of the water passages.

my gut is telling me its the radiator. i feel if it was just a fan issue it would cool down alot quicker on the highway. and now the situtate went from "cools on highway, hot in town" has gone to "once it gets warm, its super hard to cool it back down"

i think the fan is fine, no leaking silicone on the clutch. and fan stops immediatly when i shut the car off, no pinwheeling.


now should i get a nice alum radiator or just a parts store radiator. i hate to spend the dough on an expensive alum rad if a stock replacement will cool it fine.
also have spotted some nicely prices alum radiators for a fox stang on ebay, come with 100% satisfaction guarentee. that may work well.

i've had the blower on for about a year. its cooled fine before.
just started it recently and it seems to be worse now than it was a few weeks ago.

only thing i can think of that happened is i added stopleak to the coolant a few months ago fighting a WP gasket leak. perhaps that could have clogged some tubes up if there was build up already there and the stopleak went ahead and blocked it.

regardless. i ordered an alum 2 core radiator. hopefully will get it this weekend. i'll keep you guys posted on how it goes.

well guys i got my alum 2 core radiator, this thing is a beast compared to the POS i pulled out.

car seems to cool a bit better i guess. i also replaced the tstat with a 180* unit
mix is 50/50 glycol-water, also added a bottle of some coolant thinner stuff from the store.

does about the same thing, will run cool at speed but will get warmer at idle.
come to a stop and let it sit and idle the temp will creep up slowly, with the new radiator, it seems to not go up as fast but it still does.

the clutch fan doesnt seem to be bad. still feels good and has resistance to it. .
my brothers 91 lx is bone stock with stock fan, it cools fine, i took his stock fan and clutch off and it didnt change anything really.

one thing i did notice, on my bros car, the stock fan is like half covered by the shroud, the fan on my car was completely covered by the shroud. and its even further in now, the thicker radiator pushes the shroud closer to the engine.

it doesnt "overheat" but i still dont think the temps should climb from 185 ish to 210 in just a few mins idling.

and my stock fan seems to be working, i dont see how it should have a problem cooling the engine at idle. one would think a cammed engine would actually create less heat in the chamber since the VE of the engine is reduced at lower engine speeds.

i dont want to spend the cash for a new fan clutch and fan, they arent cheap.
i dont really want to do an electric fan, i mean i WOULD, but i dont feel like doing the 3g alt swap now, i am tired of throwing money at the car for now. i dont want to start spending hundreds of dollars at it.

i guess i could try a good mechanical flex fan.

only other things i think of that could cause it are...
water pump (isnt too old, like 2 years and its a parts store reman)
AC core has quite a few smashed fins.


i am guessings its still a fan issue seeing how it cools great at speed but not quite as good at slow and idling.