Thermostatic Switch?

over2land · Jun 23, 2005

I have an 88 MJ with 4.0, A/C, stick, 2WD, Dana 44 rear, manual windows and mirrors.

I'm wondering two things:

A) what temperature is the stock thermostatic switch set to come on at?

B) is the switch a ground interrupt or a Bat (+) interrupt?

Thanks.

5-90 · Jun 23, 2005

1) If you're talking about the thermal fan switch, I believe it comes on at about 220*, and goes off down around 195* or so. I'd have to check.

2) As I recall (again, I'd have to check) the switch provides a +12VDC signal to the fan relay coil. If you're looking to install an override, the easiest way to do it is to wire a toggle switch in parallel with the TFS - tap BOTH wires, run them through a firewall grommet, and wire in a switch. This will duplicate the function of the TFS, give you the ability to turn the fan on at will, and makes use of existing parts. It's not a difficult mod - I've done it quite a few times.

5-90

over2land · Jun 23, 2005

I'm looking to replace it when I go to an open cooling system as the new rad doesn't have the provision for it. And, I'm not bright enough to remember to turn it on and off.

Shouldn't it be in the FSM somewhere? I can't seem to find it in there.

And, yes, I am talking about the thermal fan switch.

Thanks.

5-90 · Jun 24, 2005

It's not h the FB - tha I reca,d (H cobd be whng...)
Why #ritch to the open system? There's no need to - I've got four XJ's runn hg blosd and no ovdrhets. ThD%clnsedvystem, properly maintained, works very well - otherwise, the OEMs wouldn't be switbhin to it d ndw paduction vehicldp!

A,po, if `u do tHd bypass/override switch, all you are adding is a means to actually turn the fan ON - i additiNj tn th TFR an thd ACPEQ signal from the ECM. If you turn the switch on, it forces the fan on. Whaaver tu`s ht o khlli.` the k$r will Dvrn it `f. If you forget to turn the fan on with the override switch, turning on the B or hiDpinf 21!200 wi` ttrn `e fan b anyho

Log story short - don't bother with the system changeover - there really pn't tht mtch f an advantage, and it'&a fair bit of Dptra work, for little to no real gain.

Oh - and let me know if ynu dd`idd torell th MJ 'coB it&s 2F@ - it &luld ma*d a goo working truck for me...

If you want to know more about keeping the `osed sIptel co`, let L` know - it&s nt that grd to i. My 88 runs down around 185, and so does my (unconverted) 89 - the o`er 89 bonvert$` bx prDriots o&her( st`l runspp around 210...

5-90

over2land · Jun 24, 2005

Well, I want the space on the fire wall for a remote oil filter as I hate the stupid upside down adapter, and a sideways adapter don't blow my skirt up either. I want to be able to put oil in my filter, and not pour it all over the place as I put my filter on.

I have to replace most of the cooling system stuff anyway (actually the only thing I'm not ditching is the heater core, only cause I don't want to take my dash apart), as my bottle doesn't seal well (the threads are wacked), all my hoses are hosed, and my radiator core is leaking anyway. I didn't want to mess with what looks to me to be formed hoses (in and out of the bottle, and to the heater core) as they are usually more expensive, and the price on a metal replacement for the bottle is 140, IIRC.

I've not overheated it yet, but since I have to replace most all of the componants, I'm just making my life easier. I don't want to burp, I don't want to pull the upper hose every year to refill/replace coolant (as it's a yearly thing for me, kinda as a system check), I don't like that bottle up on the firewall, it offends my sense of decency. Also, aside from this fitting for the themostatic switch, I'm not really seeing how it's much work. Cut some sheet metal, mount an overflow.

And, I already have the new radiator, most of the hoses, new tstat, and thermostat housing. I was going to just put a manual switch in, and forget the thermo switch, but thinking about it, cursing in traffic yesterday, I decided that my stupid ass would probably forget, and so if I could find a more eloquent way to keep the stock auto system, I would, and if there was reason to mod it later, I'd add a switch later.

UM, hate to tell you, but I'm gonna convert it to 4WD.

And, I was figureing if I could find a thermo switch that flipped on about 205, and off 185-190, I'd be golden.

Glad to know I'm not losing it by not finding it in the FSM.

And, I went looking for smilies, as I think this might have come off as me being annoyed, but I'm not... I just can't find smilies...

If any of my stock crap was salvagable, I'd prolly not be converting.

XJXJ · Jun 24, 2005

over2land said:
Well, I want the space on the fire wall for a remote oil filter as I hate the stupid upside down adapter, and a sideways adapter don't blow my skirt up either. I want to be able to put oil in my filter, and not pour it all over the place as I put my filter on.

I have to replace most of the cooling system stuff anyway (actually the only thing I'm not ditching is the heater core, only cause I don't want to take my dash apart), as my bottle doesn't seal well (the threads are wacked), all my hoses are hosed, and my radiator core is leaking anyway. I didn't want to mess with what looks to me to be formed hoses (in and out of the bottle, and to the heater core) as they are usually more expensive, and the price on a metal replacement for the bottle is 140, IIRC.

I've not overheated it yet, but since I have to replace most all of the componants, I'm just making my life easier. I don't want to burp, I don't want to pull the upper hose every year to refill/replace coolant (as it's a yearly thing for me, kinda as a system check), I don't like that bottle up on the firewall, it offends my sense of decency. Also, aside from this fitting for the themostatic switch, I'm not really seeing how it's much work. Cut some sheet metal, mount an overflow.

And, I already have the new radiator, most of the hoses, new tstat, and thermostat housing. I was going to just put a manual switch in, and forget the thermo switch, but thinking about it, cursing in traffic yesterday, I decided that my stupid ass would probably forget, and so if I could find a more eloquent way to keep the stock auto system, I would, and if there was reason to mod it later, I'd add a switch later.

UM, hate to tell you, but I'm gonna convert it to 4WD.

And, I was figureing if I could find a thermo switch that flipped on about 205, and off 185-190, I'd be golden.

Glad to know I'm not losing it by not finding it in the FSM.

And, I went looking for smilies, as I think this might have come off as me being annoyed, but I'm not... I just can't find smilies...

If any of my stock crap was salvagable, I'd prolly not be converting.

You obviously don't wanna hear the way it IS but I'll tell you this:

Converting the cooling system is ALWAYS much more work and stuff involved than you think. If hoses, cap/tank, etc. are worn-out, they're worn-out and need to be replaced. Do a custom replacement of the "system" if you want but as you are learning with this fan switch, it's not the bed-of-roses you have convinced yourself it will be. All things being in good condition, there's absolutely no advantage to either system. The factory built the one you have in your XJ for your XJ with that ECU. It's simply what it is and works fine with a little maintenance.

Check for a late model Corvette temp sensor/switch that I've heard has the same threads as the 91 and later 4.0 thermostat housing. It's practically the same electrically as the sensor you are about to trash. Of course, you'll need to source a 91 or later thermostat housing or dril/tap your current housing.

Gotta do your heater valve and expansion tank too. Shoot us some pictures when you get a complete conversion!

5-90 · Jun 24, 2005

What he said!

There really is no reason for the conversion - it's more work than absolutely necessary. If it's starting to have trouble, just put in a new closed radiator so you can do the job in an hour and call it quits. The OEM radiators typically start slacking in the 150-180Kmiles range, and the aftermarket units hold up nicely. I usually use Modine - which I can pick up locally for a good price.

No problem if you want to convert - I wouldn't mind a 4WD work truck... :wave:

There's a guy locally that has an MJ for sale, but it's an 86 and a definite candidate for restoration (which I might get anyhow...)

5-90

techno1154 · Jun 24, 2005

I have one of those switches taken from a '89 XJ that I am using to run the electric cooling fans. It come on at 200* and go off at 185*. I prefer this over the computer controled switch that come on at 130* +.... too hot for my liking. In OEM installed applications, I do not know wether or not they are wired + or -.

over2land · Jun 24, 2005

XJXJ said:
You obviously don't wanna hear the way it IS but I'll tell you this:

Converting the cooling system is ALWAYS much more work and stuff involved than you think. If hoses, cap/tank, etc. are worn-out, they're worn-out and need to be replaced. Do a custom replacement of the "system" if you want but as you are learning with this fan switch, it's not the bed-of-roses you have convinced yourself it will be. All things being in good condition, there's absolutely no advantage to either system. The factory built the one you have in your XJ for your XJ with that ECU. It's simply what it is and works fine with a little maintenance.

Check for a late model Corvette temp sensor/switch that I've heard has the same threads as the 91 and later 4.0 thermostat housing. It's practically the same electrically as the sensor you are about to trash. Of course, you'll need to source a 91 or later thermostat housing or dril/tap your current housing.

Gotta do your heater valve and expansion tank too. Shoot us some pictures when you get a complete conversion!

Yeah, I'm sure there will be issues...

But like I said, I already started down the road, before I was able to be convinced that the old system can work... I mean, look how many are out there and not exploding. But, having dived in and bought parts before that, here I go.

Sure, I'll put up some pics when I'm done.

Good info on the vette, I'll check it.

And, I'm still torn between keeping my heater valve, and going with the newer one. Mine's metal... but I hear the new plastic one completely stops any heat from getting to the core.

Thermostatic Switch?

over2land

NAXJA Member #1171

5-90

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over2land

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5-90

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over2land

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XJXJ

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5-90

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techno1154

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over2land

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