fan wiring question; to stay on after shutdown?

so I have that odd problem where on hot shutdown, if I let it sit between 10 and 25 minutes or so upon startup the xj runs rough due to the #3 injector having gas that is vaporized/too hot... I have a manual fan switch installed and if I leave that on while its parked (or just park when the engine is at 180-195) I don't have a problem on startup. Anybody know of a good way to setup the stock fan wiring to run even if the engine is off until it cools off a bit?

rewire it hot to the battery through a relay

CommandoXJ96 said:

so I have that odd problem where on hot shutdown, if I let it sit between 10 and 25 minutes or so upon startup the xj runs rough due to the #3 injector having gas that is vaporized/too hot... I have a manual fan switch installed and if I leave that on while its parked (or just park when the engine is at 180-195) I don't have a problem on startup. Anybody know of a good way to setup the stock fan wiring to run even if the engine is off until it cools off a bit?

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Fan switch just like you've got?

Honestly, anything else would require a "delay relay" - which you can find from various industrial electronic supply houses (I'd start with Allied Electronics - www.alliedelec.com.) However, I don't know how many of those would be rated for 12VDC - I've usually seen them for 48VDC, 96VDC, 120VAC, 240VAC, and the like.

Second approach would be to build a timer circuit to drive the relay - you could do one with OTS parts to get yourself a shutdown time on the fan of anywhere up to five minutes or so without too much trouble.

OR - I seem to recall that there was a TSB on later models about pretty much this very thing - and that installing a heat shield was the fix for it. Perhaps you could check into that? Building a heat shield for at least the #3 injector (which is, I think, where the TSB trouble was anyhow...) out of sheet aluminum might also solve the trouble without having to leave the fan on after you shut down...

a temperature activated relay powered by the battery. I got mine from Jegs

I fail to see how a fan cools an engine that is not running....I mean the coolant isn't circulating through the engine.It stays in the radiator.

The only reason I could see to make your fan stay on after shut down is to avoid a hot start up condition.
Like say After you've driven for a while and the motor is up to operating temp and you park and shut the engine off for only a few minuets and then suddenly remember you left something at the bank and jump back in and start the motor only to see that the motor has heat soaked the coolant in the engine.A fan that stayed on for those few minuets you parked would have cooled the coolant in the radiator and only in the radiator.

outlander said:

I fail to see how a fan cools an engine that is not running....I mean the coolant isn't circulating through the engine.It stays in the radiator.

The only reason I could see to make your fan stay on after shut down is to avoid a hot start up condition.
Like say After you've driven for a while and the motor is up to operating temp and you park and shut the engine off for only a few minuets and then suddenly remember you left something at the bank and jump back in and start the motor only to see that the motor has heat soaked the coolant in the engine.A fan that stayed on for those few minuets you parked would have cooled the coolant in the radiator and only in the radiator.

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It's not cooling the engine as a whole. However, what is is doing is circulating air through the engine bay - which can be useful for trying to keep some small components cool (like fuel injectors.) That's what he's after here - he's trying to keep his fuel injectors from getting vapour-locked after he shuts down. Forced airflow can help that.

Yes, a cooling fan will make a "cold slug" of coolant in the radiator, but that's not what he's after here. If he had hood vents, I'd suggest putting a small fan in the one over the fuel injectors and having that run on a timer after engine shutdown - it would probably be of more help to him (have it set up to draw cool air in flowing over the injector, rather than blowing out the vent and drawing hot air over the injector from the exhaust, by the by...)

However, this is a "next best" solution, using what he has handy. It's not perfect, but it's a start (a perfect solution would be a cross-draft head so that the injectors aren't overtop the exhaust manifold, but that would take far more engineering than we're ready to do...)

5-90 said:

OR - I seem to recall that there was a TSB on later models about pretty much this very thing - and that installing a heat shield was the fix for it. Perhaps you could check into that? Building a heat shield for at least the #3 injector (which is, I think, where the TSB trouble was anyhow...) out of sheet aluminum might also solve the trouble without having to leave the fan on after you shut down...

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X2 I think I saw the write up on here a few days ago.

My 2001 has the same problem even after trying the insulator fix.
I added a manual fan switch and relay for use on hot days or for trail use.
I have been thinking about adding the 12-volt delay relay shown below.
It will only switch 7-amps, not enough for the fan, so a 40-amp Bosch-type relay will still be required.
Something to think about.

ELK -960 Timer rely
http://www.hometech.com/brains/timers.html

lazyxj said:

My 2001 has the same problem even after trying the insulator fix.
I added a manual fan switch and relay for use on hot days or for trail use.
I have been thinking about adding the 12-volt delay relay shown below.
It will only switch 7-amps, not enough for the fan, so a 40-amp Bosch-type relay will still be required.
Something to think about.

ELK -960 Timer rely
http://www.hometech.com/brains/timers.html

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So isolate the signal using diodes, and use the delay shutoff to trip the OEM relay. No sense complicating things more than necessary, you know?

thanks for the suggestions guys!

the hood vents would actually help with that quite a bit now that I think about it... close to the injectors on the driver side.

I actually had the jeep do this to me around 10:30... I don't think it impressed the girl I was picking up (i shut down the car and came back exactly 10 minutes later; just enough time to vapor lock the whole rail apparently). Ran great all the way to phoenix (100 miles there/another 100 back) from 6 to 10pm though :|

i gotta do something about this now thats its warm outside here again!

edit: oops, double post.

5-90 said:

So isolate the signal using diodes, and use the delay shutoff to trip the OEM relay. No sense complicating things more than necessary, you know?

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Tried that with a fan override switch and got a CEL.
I surrendered and added a new relay.

The late model OBDII is sensitive to so many things.
It cannot be locked into !st or 2nd gear with a CEL.

1: I like hood vents. They keep the under hood temp down without putting any load on the battery.
2. Rising the back of the hood has worked for a few. A inch or two seem to work.
3. The stock E fan can be wired in some cases to run on in the key off mode. Pre 96 I think. Before the computer took over it's operation. I did a Tempo that way. It stop burning up module after that.
4. Just pop the hood on hot days.

Im new to the Jeep scene, so take this for what it is worth. But if it is an ODB II system and if there is any type of software out there that allows you to program the engine computer at all, you can set the fans to run after the engine is turned off.

I have a Grand Prix in which I have done this very thing to. I have the Grand Prix set to run 120 seconds after the engine is shut off if the coolant temp is over 180*. I plan on eventually tying that into an electric water pump so there will be coolant flow on top of that. There are after market plug and play harnesses in which you can manually control the fans without setting off the CEL, but reprogramming the ECU seemed a much better way to do things for that vehicle.

Again, I havent learned all whats available for the Jeeps yet, just an idea.

SyntheticShield said:

Im new to the Jeep scene, so take this for what it is worth. But if it is an ODB II system and if there is any type of software out there that allows you to program the engine computer at all, you can set the fans to run after the engine is turned off.

I have a Grand Prix in which I have done this very thing to. I have the Grand Prix set to run 120 seconds after the engine is shut off if the coolant temp is over 180*. I plan on eventually tying that into an electric water pump so there will be coolant flow on top of that. There are after market plug and play harnesses in which you can manually control the fans without setting off the CEL, but reprogramming the ECU seemed a much better way to do things for that vehicle.

Again, I havent learned all whats available for the Jeeps yet, just an idea.

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There probably is, but you run into the difficulty that the interface/reflashing software is somewhat proprietary.

With GM, it's simple. You build the interface, you buy a copy of their software, and you're done. You can get updates from GM as you need them, or as they come out with updates to OBD-II.

With Ford and Chrysler, it's not so easy. Ford and Chrysler don't "sell" their software, they "lease" it - Ford for somewhat less than Chrysler. A Chrysler software "lease" is something like $2500/year (Ford was, I think, around $1200-1500,) and that makes it rather prohibitive.

I found this out from a local PROM-burning tech, who does GMs all the time. That's got a lot to do with my wanting to put the GM OBD-II V6/DIS system on the 4.0L - I can burn a compleat new PROM with a new fuel/air/spark map to fit the 4.0L for less than I can try altering the programme on the ChryCo.

You've got a sound idea, just needed more information to find out why it won't work so well (I didn't say it won't work at all - but it gets spendy. Fast.)

There's mention of a timer relay. My 2000 keeps the headlights on for about a minute after shutting down with headlights on then turning off lights. Lights stay on , I think by a timer relay. Not sure if there are longer duration T-relays out there, but at least I think they exist for 12volt systems, unless my lights are controlled by the OBDII. I have not checked this circuit out, so not sure, just wanted to mention possible presence of timer relays already used on some jeeps.

Here's a relay that may work...
http://www.amazon.com/NTE-R27-11AD10-12-Programmable-Repeat-Cycle/dp/B000Y3QTR6


Here's some tossed up ideas!!
There are electric water pumps out there that would serve this purpose of cool-down system idea. Though I'm sure the pump's reliability is no match to a mechanical pump. But just think, if they were worth the conversion, you could put a thermal relay to power secondary higher rated relay(s) to keep the electric fan(s) and elec. pump on to cool the entire block down to a desired level. Of course it would be wise to have all this electrical powered by a deep cycle battery isolated from the starter battery. And even the use of hood vents would improve this settup.

Well just an expensive idea not for me or my starved wallet anyhow, and not rure if it would hold up to trail abuse or not. I did a little research on the idea, so here's the pumps and stuff I found...
http://www.jegs.com/webapp/wcs/stores/servlet/category_10001_10002_10135_-1_10131
http://www.jegs.com/p/Moroso/744357/10002/-1/11465 -- Best route for electrical conversion by price and for light trail use imo, but carry spare motor just in case!
http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID%3A2009544&TID=800&TID=800&productId=2009544&catalogId=10101

well in response to the CELs; its only the 97+ that throw a CEL when you begin messing with diodes and stuff. I actually have the 1st/2nd gear switch mod done and the 96 has never thrown a CEL from it, so it probably won't throw one from me messing with any diodes.

im kinda leaning away from the idea of the electric water pump, for both the reliability issue, as well as the fact that the injectors vapor locking issue can be fixed without doing that much extra work.

im gonna follow one of these routes to keep my fans on after shutdown via timer (instead of a manual switch - ive killed my battery with the taurus fan pretty quick before) and add at least one vent on the driver side.