how hot is too hot

1689 Views 12 Replies 5 Participants Last post by alfettagtv2000, Mar 17, 2008

alfettagtv2000

Discussion Starter · Jan 2, 2008 (Edited)

some time ago the radiator core needed replacing. the guy at the radiator shop convinced me to get a heavy duty core. now while this is a good thing i have noticed differences in city traffic:

the fan switches on at 92-98degC and turns off at 82degC (the fan used to switch on at 89degC and switch off when the temperature fell to 79degC)
temperature recovery time is normal

what would be the reason for this change?
is this normal behaviour?
any ideas would be welcomed.

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1 - 13 of 13 Posts

G'Day Nick,

Food for thought isn't it?

I don't know if I should call this a guess or an inkling of a thought but:

Maybe the radiator is to big for the flow rate?

Consider water flowing through a grate into a drain, if the flow rate is low the water trickles down through the grate only at the point closest to the inlet. Not until the flow rate is high is the whole grate used.

Let the debate begin

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la_strega_nera

· #3 · Jan 3, 2008

temperature operated switches often drift temperature wise over time....

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alfettagtv2000

Discussion Starter · #4 · Jan 4, 2008

Craig
Maybe the radiator is to big for the flow rate?

so what is the difference between the standard core and a heavy duty core?...i thought the only (visible) difference was the density of the cooling fins...
from your analogy it would suggest that passages in the core are also larger. therefore at slower speeds the radiator's ability to retain more heat and 'delay' the temperature switch sensing 92degC is increased. this would explain the difference...

la_strega_nera
temperature operated switches often drift temperature wise over time....

perhaps the problem does lay in the switch

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Tifosi

· #5 · Jan 4, 2008

Mabe it just seems to act a bit differently now as it's cleaner and better flowing?

You give the 'used to' numbers which presumably were from before the re-core and there must have been some reason for that to begin with, correct?

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alfettagtv2000

Discussion Starter · #6 · Jan 4, 2008

Tifosi said:
Mabe it just seems to act a bit differently now as it's cleaner and better flowing?

You give the 'used to' numbers which presumably were from before the re-core and there must have been some reason for that to begin with, correct?

yes the 'used to' numbers were from before the recore...
the haynes manual states:
electric cooling fan "cut-in temperature" 82degC to 92degC (180degF to 198degF)...
from that i believed that things were in working normally (before the recore)

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Craig

· #7 · Jan 4, 2008

Nick, silly me, I thought you'd gone from a double core to a triple.

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beatle_bayly

· #8 · Jan 6, 2008

alfettagtv2000 said:
some time ago the radiator core needed replacing. the guy at the radiator shop convinced me to get a heavy duty core. now while this is a good thing i have noticed differences in city traffic:

the fan switches on at 92-98degC and turns off at 82degC (the fan used to switch on at 92degC and switch off when the temperature fell to 79degC)

temperature recovery time is normal

what would be the reason for this change?
is this normal behaviour?
any ideas would be welcomed.

My guess is that the switch is simply reacting to being moved into a new home after some 27 years undisturbed

Are you absolutely certain that the fan wasn't operating identically prior to the new rad. Lots of times we only take a close look at these things after the fact and suspect a change when in fact there isn't. Alfa guages aren't perfectly accurate, and the needle itself would cover a few degrees in it's width.

Kinda like how much better a car runs after you wash and polish it to put it up for sale

It's also probable that the new rad flows differently to the old one ( and I'd hope it does too or you wasted your money on a new rad). The fan switch senses coolant temp in an entirely different spot to the guage sender which could account for the anomaly. Also, the system may simply be reacting to changes wrought by a good flush and new and possibly different branded coolant.

If you are really concerned about the temps, use an external guage to test the system and don't rely on the old Alfa guage.

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beatle_bayly

· #9 · Jan 6, 2008

alfettagtv2000 said:
Craig
--------------------so what is the difference between the standard core and a heavy duty core?...i thought the only (visible) difference was the density of the cooling fins...
from your analogy it would suggest that passages in the core are also larger. therefore at slower speeds the radiator's ability to retain more heat and 'delay' the temperature switch sensing 92degC is increased. this would explain the difference...

By my understanding a 'heavy duty' core should have finer passages, but more of them. This should see no change in the amount of water flow, or maybe a slightly better flow rate, but there is substantially better heat exchange across the radiator realising more stable temps.

Another thing I just considered is that a new thermostat may have changed the flow characteristics even when full open. A good tune up could also change the engine temps at the head. Remember, you are only noticing a coolant temp change of around 5degC which is bugger all in the bigger scheme of things. And, the temp of the coolant is NOT necessarily indicative of the heat of the valves or head around the valves.

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alfettagtv2000

Discussion Starter · #10 · Jan 29, 2008 (Edited)

radiator comparison

original radiator:

27x2 sets of water passages
cooling fin pattern 'wwwww'

heavy duty radiator:

28x2 sets of water passages
cooling fin pattern 'ununun' spaced closer togrther

the cross sectional area of the water passages seem to be the same for both

for the same pump flow rate is the water running through the passages travelling at a slower velocity?
can this explain the increased temperture set point for the fan switch?

(the fan switch is a veglia marked with 86-76)

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beatle_bayly

· #11 · Jan 29, 2008

Dunno

I'd say the form of the cooling fins is simply down to the manufacturer of the core. Your HD radiator doesn't sound any more HD than the previous one.

But if it's really worrying you, go buy an aftermarket adjustable thermo switch. I think Davies-Craig make the ones where you feed the copper sensing line and bulb up the radiator hose, under the clamp. Simple screwdriver adjustment of the thermostst to change the activation temp.

My '79GTV had one of these and it worked perfectly for 14 years/270,000km. I also fitted one to the Duetto along with an electric fan.

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alfettagtv2000

Discussion Starter · #12 · Jan 30, 2008 (Edited)

electric fan thermostatic switch

thanks beatle...

i went for a bit of drive this morning (an italian tune up) just to check the cooling system again...

with an ambient temperature of approximately 22degC the engine temperature remained mostly at around 80-85degC with a high of about 96degC after a long climb..

when i got home i let the engine idle for a bit so that the fan switch went through a few cycles of turning on and off ...

fan switched on at 89degC
fan switched off at 82degC

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alfettagtv2000

Discussion Starter · #13 · Mar 17, 2008 (Edited)

i just went for a nice drive on the weekend (3.5 hours)...
the weather was fantastic...
the temperature outside must have been in the 30's...
the car performed well and the temperature sat between 85-92degC on the freeway but did get to 98degC in stop/start traffic (it dropped fairly quickly when on the move again)..

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