Cooling fans

[mt308]

I find once my fans have switched on at about 85-87 degrees they hold the water temperature at about that level if in slow moving or stationary traffic. Once on the move (motorway speeds) it cools down to about 82 degrees or so (all temps according to the standard Ultima gauge). But in this weather (not really hot but warm - low 20s) the fans then stay on constantly even after a good 15 minutes on the motorway and into slower traffic. It seems to have to get back down to 80 before they switch off....and it rarely returns to that.

So on a mixed run, some motorway, some single lane roads, some traffic I generally find once I've been in traffic the fans then stay on until I turn the engine off at my destination.

I have no over-heating issues at all (on an earlier post here I mentioned sitting in solid traffic in heat for 4 hours without going above 90 degrees) but it seems odd the fans are on the whole time under fairly normal driving conditions (e.g. 80mph in clear air for 15 minutes or more).

Is this normal?

Thanks

Mark

[Steve_D]

Sounds like your fan switch is not working as you would like.
I replaced mine some years ago with a Kenwood adjustable stat whic does just what I want.

Guy (bluesatin) found this unit
http://www.ebay.co.uk/itm/DC-12V-Digital-Temperatu...

and some more info.

http://www.autospeed.com/cms/A_112617/article.html

I'm so impressed I've ordered one even though I don't have an immediate use for it.

Steve

[5paulmv]

Can you plug into your ecu and adjust when the fans turn on and off . We have just been playing with this mine come on at 78 c and then turn off when temp drops to 75 c

[356Speedster]

Where is your temp gauge reading from, what fans are you using and are you using the std sensor / fan switch? That behaviour doesn't sound at all right to me, but any number of things could impact it....

FYI, I read water temp from the GM temp sensor on the LHS cyl head, via the GM harness & ECU. The ECU triggers the fans direct. Basically, I've replaced all Ult parts of this circuit with that of the GM harness & kit. I also use larger Pacet fans on the std Ult rad. Fans come on c.96 deg if I remember correctly and go off around 88 deg. Even in 30 deg ambient heat, in stop/start traffic, the fans will cool the water and switch off in 5-10mins, without fail.

ETA....

5paulmv said:

Can you plug into your ecu and adjust when the fans turn on and off . We have just been playing with this mine come on at 78 c and then turn off when temp drops to 75 c

That seems a bit too cool to me.... LS motors run pretty cool, but I was lead to believe you needed the water to warm up in order to help bring the oil upto a good temp. My car will warm up it's water to 80+ very quickly, but still it takes 15mins+ to get the oil upto 75 deg.

Edited by 356Speedster on Wednesday 21st August 21:17

[anonymous-user]

It's always a tricky balance finding an appropriate trigger temperature and hysteresis band for turn on single stage fans. Pretty much every OEM has now gone to variable speed fans to make life easier (and of course in the name of fuel economy etc)

If the fan switch is on the radiator exit (bottom hose) then using a lower setting can be advantageous to account for the radiator temperature drop.

[BobE]

In the past I had a similar problem when I bought an LM500 Marcos. That was even worse - when the fans turned on they wouldn't turn off until the engine was turned off and cooled down. The cause was a mismatch between the engine thermostat and the temperature switch that turned the fans on and off. I can't remember all the exact figures but it was something like a 78 degree engine thermostat and a temperature switch that turned the fans on at 85 degrees and off at 75 degrees. So if the engine heated up to over 85 degrees the fans came on but wouldn't then turn off as the engine thermostat kept the water above the 'off' point of 75 degrees. It may not be the cause but it's worth looking at.

[F.C.]

356Speedster said:

That seems a bit too cool to me.... LS motors run pretty cool, but I was lead to believe you needed the water to warm up in order to help bring the oil upto a good temp. My car will warm up it's water to 80+ very quickly, but still it takes 15mins+ to get the oil upto 75 deg.

Edited by 356Speedster on Wednesday 21st August 21:17

According to previous threads this is not the case for LS series motors :
Granted LS motors have more efficient cooling, but that is because they are designed to run leaner/hotter for efficiency and emissions purposes.
Apparently the following is normal for LS2 through LS7 :-
Normal running 195-200f (90-93c)
In slow traffic 215-225f (101-107c}
As in the previous thread the perceived hot running is just that "perceived".
Trying to run you motor at Circa 80c degrees is a fast way to a worn engine.

At the end of the day the temperature spec of the thermostat has little or nothing to do with the operating temperature of the engine. It controls how fast it warms up. If your engine wants to run at 190, it will run there no matter if your thermostat is 160 or 180. The operating temperature of the engine is controlled by the efficiency of the cooling system, size and condition of radiator, condition of the cooling galleries, silt in the block, etc. If your engine is overheating in traffic, changing out a 180 thermostat for a 160 won't make any difference. The only time the thermostat would come into play is if the cooling system is super efficient and the normal operating temperature is below the spec for the fitted thermostat.
Running rad fans at low "on" temps is only stalling the process of the engine getting to "its" operating range.

Turned this up regarding SBC:
Most people have been led to believe that 180-190 degrees is ideal, so they start to panic at about 200 degrees. Wrong. If we assume that your cooling system can maintain an operating temperature within about a 30 degree range under most driving conditions, then you should select a thermostat that will keep the operating range in the 190 to 200 degree range. Parts failure on a properly maintained engine should not be a consideration until water temperatures reach 250 degrees or higher.

Source:
General Motors Performance Parts
Crate Engines
Frequently Asked Questions

Edited by F.C. on Wednesday 21st August 23:25

[Storer]

My LS7 with GM ECU senses temperature at the head and switches the fans on at 90 degrees C. Why wait until the water is too hot at the radiator?
Off again at about 87 deg.

Motorway/A road running is normally 78 to 84 deg and only in very slow traffic does it creep up above 90 deg.

No cooling issues.


Paul

[DHGTR]

Its all perception again.
As we have grp rear clips, no insulation(apart from exhaust area), complete exhaust system in the engine bay, grills that let heat out, it always seems very hot 'to us' in that area.

Has anybody ever broken their Ultima because of the water temps?
Do we all think the factory/Amerspeed have got it completely wrong?

My oil is also cooled by the water system but i dont have water spluttering out because of over temps.

I just think we may be giving out a negative idea of the car to neutral readers and possibly your future purchasers, when in fact all we are doing is tinkering around and trying to mend something that 'aint broke'.

[deadscoob]

Agreed.

Also agree with FC.

[356Speedster]

Agree with FC, I think we're saying the same thing....

There's have been a lot of discussion on cooling and people get quite wound up over it, but I'm not aware of anyone who's cooked an LS under normal circumstances (i.e. outside of a technical failure). If anything, I'd say my engine sometimes feels over-cooled.... on a light throttle cruise, the water holds rock-solid at 88deg, but the oil cools down to 60deg... that's why I say the LS runs pretty cool.

In stop/start traffic in 30deg heat in France, it took a long time for me to see 100+ on either side (and I'm sure that was mostly due to exhaust heat soak) and certainly, the fans were always able to cool the water & switch off.

I guess due to the nature of these cars (to quote Ted, they're a hobby!) and with states of tune, components used, setups etc all varying, then needs will be different and cooling needs to be appropriate. As a 480'ish BHP LS3 owner, letting the ECU run the fans from it's cyl-head mounted sensor, I have no high temp concerns, so hopefully that helps to give a bit of a baseline.

[UltimaCH]

As the cooling system is pressurized, I would think that if you are not seeing any water spewing out of the expansion tank bypass pipe, your engine is not overheating. 100°c in a pressurized system is certainly not the same as 100°c in a non pressurized system.