Engine and Transmission Tech

Should the fans come on at same temp as thermostat opens? Lower temp? Or, higher?

I think the fan should come on about 10 degrees higher.

You need to consider not only the "on" temperature of a thermo switch but also the "off" temp as well. For example, your thermostat starts to open at 180* and maintains engine temperature at 185* under normal conditions. Some temperature switches have an on temp of 190* and an off temp of 180* (it is normal to have the off lower than the on temp). So your engine temp climbs to 190* and the fan turns on but the thermostat will maintain engine temp at 185* so the temp sensor never sees the 180* it needs before it shuts down. Just something to think about because you don't want the fan running all the time.

Good point Jim.

I'd love it if my thermostat/radiator combination could maintain engine temp but it's not close. Just sitting at idle the fan cycles on & off -- I guess that makes sense since there's no air flowing then -- and I don't know when my fan is on when I'm driving because I can't hear it. Maybe I need to wire an indicator light to it - might be telling. I made the shroud that's on it & it's only about 1/2" away from the core. I've wondered if it's blocking air flow when driving.

Right now, I'm running hotter than I want to. Idling in the driveway it'll stay between 180 & 185 or so all day long (180 thermostat; 185 fan switch probe). Driving around town, it climbs up to 210 or so & doesn't come back down -- even if I sit at idle for 10-15 mins. I've flushed the radiator, bled it to make sure there's no air trapped, & checked the radiator & cap for leaks - all checked out ok. Plugs look good. Also ran air into the left cylinders to see if I'd get bubbles in the radiator -- no bubbles. Ran out of time but plan to check the right bank too.

Only other thing I can think of is maybe my fan motor was compromised a month or so ago. Not sure why, but the fuse holder melted. It was supposed to be rated for 30 amps, but I got it from Amazon so don't know for sure. I replaced it with a NAPA holder but maybe the fan overheated somehow & isn't pulling as much air now? Not sure how to test that though because I don't know how many amps it should be drawing.

Rob

It sounds like a couple possible issues. Since it heats up when you are driving around and I assume you have a new radiator (not plugged) that you have an airflow problem. I also assume others have used the same radiator with success (it has enough capacity). The engine produces more heat when you are driving vs idling so the fan has sufficient airflow at idle but the total airflow when you are driving is not sufficient to remove the added heat. Curtis wrote a really good tech article about where to locate a cold air inlet for the engine and it has good information about measuring pressure differentials with a Magnehelic gauge. You need to measure the pressure in front of and behind the radiator while you are driving. Too bad you don't live out here in God's country, I could let you use mine. You can find them on Ebay for really cheap sometimes, look for a 0-1" of water or a 0-2" of water unit. If there isn't a good pressure differential the air isn't going to flow. You need to have the front of the radiator completely sealed off from the rear so that every molecule of air entering the grille has to go through the radiator and not around it. You may have to vent the engine compartment if you have pressure building up, the wheel wells are usually a lower pressure area and louvers about half way back on the hood are also a good location.

If everything is OK airflow wise you should check out the distributor advance and make sure it is working. Retarded timing will cause overheating. Watch the timing mark as you rev the engine and see if it goes up over 30*. Lean mixtures can also cause it to run hot but that probably isn't an issue unless you have a huge vacuum leak.

The melted fuse holder is worrysome. Not sure what kind of fan you have but you need to be running a big capacity relay for the fan like a 75 amp since some of the OEM fans draw huge power on start up. OEM fans are the only way to go as they move way more air than any of the aftermarket stuff and most have nice shrouds built in also. I have a 18" diameter Lincoln Mark VIII fan that draws 100 amps on inrush and 45 amps running on high but it also pulls an actual 4500 cfm. If you run a fuse at all it better be a big sucker.

Lots to check, good luck.

Quote:

OEM fans are the only way to go as they move way more air than any of the aftermarket stuff and most have nice shrouds built in also. I have a 18" diameter Lincoln Mark VIII fan...

The fan was the biggest I could find that would fit but it's nowhere near 4500 CFM. It's about 2500 if memory serves. But, I think it was enough because it was working fine for a while. In case it did get damaged when the fuse holder fried, I'd be interested in suggestions of OEM fans to check out. The core is 15 1/2" wide X 19 high. Could go to about 17" wide overlapping the tanks. And I have 3 3/4" from the face of the core to the water pump pulley (could get a little more if I redid the radiator support brackets to angle it a bit forward at the bottom).

Rob

I would look for a Taurus fan at the local Pick-a-Part. The fan is 16" in diameter and moves 2,500 cfm on low speed and over 4,000 cfm on high speed. My local yard is having 1/2 price sale this weekend and electric fans are less than $20. The shroud is 21 1/2" x 17" x 4 1/2" but could easily be cut down to 19". The depth could also be reduced by trimming the shroud where it mates to the radiator but would work better if you don't have to. Google "Taurus fan" and you will have plenty to read. Again, high cfm means high current draw so no wimpy hookup. 8 gauge wire all the way from the battery, 75 amp relay and big or no fuse. I would also hook it up to run even with the ignition off so it shuts off only when the water temp is low enough to trigger the sensor - prevents after-boil.



Edited 1 time(s). Last edit at 07/31/2012 11:36AM by Jim Stabe.

Well, I found the culprets... one main one and a 2nd less urgent. First, I need to upgrade my fan relay and socket....


My fan says it draws 27.5 amps so i could use a 40 amp set-up but I'm going to use something that'll handle a Taurus fan in case I need to swap for one of those when I get my a/c going.

Second item is my overflow container is barely big enough. When my radiator cools is sucks back all but 3/8-1/2" of the water so I have to watch it or after a few days evaporation would lead to air in the system.

Rob

If you want something that will definitely work, use one of these (and they're cheap too) They are used to switch motorhome power on and off, good for 80a continuous and 150a in rush

[www.surpluscenter.com] This one makes the circuit by grounding the small terminal.

[www.surpluscenter.com] This one makes the circuit by applying 12v to the terminal and it grounds the signal circuit through the case

If you don't know about Surplus Center you should poke around while you're there, they have lots of neat stuff

I'd seen some similar to that when I Googled around for relays but hadn't run across that site. Thanks!

Rob, I haven't posted on the forum for awhile now but I'd like to throw in some words of caution concerning electric fans. You may not always want your fan to come on while cruising as it may interfere with the natural high speed air flow. Most factory vehicles have this function controlled by the computer to disconnect power to the fan while the car travels above a pre-defined speed; Here's a link to an after-market gadget from Ron Francis, it's a little pricey but may solve some cooling problems that might occur while cruising:[www.ronfrancis.com]

Cheers,

Jacques

Note, that high power relay pulls almost a full amp of current at the winding. A solid state relay will do the job reliably with no moving parts and at a reasonable cost.
[www.teledynerelays.com]

Jim

Could not the initial melting be caused by the fans coming on at full power? Would a staged startup not have a lower draw?
Also by having the sensor/trigger for the fan in the water pump inlet, rather than thermostate outlet, you would likley never have the fan running while at hiway speed.

Jim B

Who sells those relays, those are cool.

Bunch of places, like Digi-Key, Hosfelt, even Radio Shack maybe. For higher currents they need a heat sink of some kind but just mounting on a panel helps. Watch out for the AC ones though, if used with DC they don't turn off.

Jim

Those Teledyne relays are $350, yipes!!

That seems quite high. I'd expect a price closer to 20 bucks.

Jim

Here's what came up when I Googled the p/n

[www.onlinecomponents.com]
[www.alliedelec.com]
[octopart.com]

At $20 I'd take two of them but $350 is rediculous!

Mike - could be but the way the fan is designed, there are two hot wires. One hot = low speed, both hot = high speed. The only way I can think of to wire it so it'd come on low & switch to high would be to use two relays with one being a time delay relay. Cost of suitable amperage time delay relays is way more than one like what Jim suggested.

The idea of putting the sensor at the water pump inlet I interesting. Effectively it'd simply be reading the temp after the water has been cooled in the radiator - so fans would come on only after engine was a good bit hotter. How would that affect engine temp at stoplights or in traffic?

Jacques - good info. I don't think my fan is running when at speed - at least when the wiring isn't fried. But, I do have an unused LED in the dash so am going to wire it so I can see when the fan is on. If it is coming on at speed, I'll have to look into one of those. Thanks for the tip!

Rob,

You would need the sensor to be of a lower temp range than if in the rad inlet.
I bought a flex a lite variable switch but have not installed it. Starts fan at 60% and then increases to 100% over the next 10-15 F. Initial start temp is variable from 150 and up.
No longer in Houston so car does not see your degree of heat anymore!