Hey guys...

I dunno if i am the first, but i think i have solved the problem of not being able to install a switch for an electric rad fan on a pre-3rdgen 350 (like my '79 350). I have yet to actually test this, but it is all installed on my car and is all working (but too late at night to start the car). If you want to know, this is what you do...

- Go to the parts store and buy a temperature sensor/sender for a *temperature warning light* for a 350 of your year or similar. It is the same size as the temp. guage sending unit on the drivers side head between cyl. 1 and 3.

- Remove the cap in the passenger side head between cyl. 6 and 8, which is between the spark plugs. *** Be careful, there is coolant behind this plug and it will come gushing out as soon as the plug is out.*** You will need a 3/8" socket extension to take this out (no socket, just the extension with the square end). BTW, this was the hardest part.

- Put the sensor into the hole you just took the cap out of and thread the new sensor in by hand untill finger tight, then you have to torque it down to 20 ft-lbs. My sensor needed a 15/16" deep socket to fit the sensor. Others could be different, but probably not.

- Cut the connector off the wire that is supposed to plug onto a regular fan switch and install on a spade-type connector end. Disconnect the battery, plug the wire onto the sensor and try it out. It may not turn on untill a degree or two higher than the fan switch would, but i doubt this is anything to worry about.

BTW, i have not actually tried the setup yet because i had no time to start my car tonight, but i will report results tomorrow. Wish me luck.....

 

That is not what you do. That's dangerous, to say the least. Very bad work-around.

The right thing to do is to go buy the right fan switch in the first place, or re-use your existing one; and go to the hardware store and get a 3/8" - ½" pipe brass bushing to put it in with.

Get rid of that and do it right, you'll regret the consequences of what you've got. Just because it's electrical and holds coolant in doesn't mean it's going to work right.

As usual, almost anything that involves cutting wires is WRONG. If you use the right switch and install it correctly you don't have to cut anything.

 

This is disappointing to hear, but thanks for the heads up

Why is this so dangerous? I understand that this isn't really the "proper" way to do it, and if it doesn't work, i can still manually turn the fan on. I want to do it the way you are saying to, with the adapter, and even have a brand new fan switch in my room as i am writing this, but i cannot find this adapter anywere!!

What is the inner/outer thread size i need to use my fan switch? It is just a stock replacement for the HO 305 motor.

 

I just bought about 4 of them at Home Depot the other day for use in my air compressor system. Go to Home Depot.

The reason it's dangerous, is because the warning light switch comes on at like 260°..... way too high for use as a fan switch. Your engine will reach red-light temperature before the fan comes on, in case you don't flip it on yourself, like if you walk away from the car with it running. A factory fan switch comes on at 230° or so.

The outer thread size that you need (the hole in the head) is ½" pipe. The fan switch threads (the hole inside the bushing) is 3/8" pipe.

It's in the plumbing section, with all the other brass fittings.

 

Ok, thanks alot RB... I knew the sensor would activate at a higher temp than the switch would, but i didn't think it would be THAT much higher... i was thinking maybe 5* above running temperature, because there was nothing to be found that says at what temperature the switch activates.

Well, I am glad to hear that that was what you meant by dangerous, because I had a bad feeling it would be something alot worse that would really cause problems. This is not too much of a problem as i have become accustomed to manually turning the fan on myself over the last 3 or 4 months, so i guess i will stick with that for now.

Is there another size of fan switch that i could use? I brought it to both a parts store and Home Depot (thanks for the idea btw) and neither place has an adapter that is small enough on the outter thread to fit the 350 head and is big enough on the inner thread (9/16" i think) for the switch. This has been my problem since mid-October.

Is there a switch i can use with a smaller thread size so i can use a different adapter? Maybe something like 5/16" or so?

 

I'm telling you, it's there....

Go to the plumbing section. Look where the brass compression, flare, etc. fittings are. They have a chart on the wall with every style of fitting, color-coded. IIRC toward the left end of the chart is all the pipe-thread stuff. Look for "bushing"; ½" pipe outer, 3/8" pipe inner. Those are the numbers you need. Not 9/16" thread, none of that sort of thing; just ½" x 3/8" pipe bushing. That's the name of the part in question.

Pipe threads aren't measured the same as bolt threads. They're something completely different. They're tapered, so when you screw one into another, they jam together. Use about 4 wraps of Teflon tape on them.

I'd post a pic of the one I have in my double-hump heads right this very minute holding a stock fan switch, or the ones that hook my 3/8" air compressor outlet to the ½" ball valve and then back to the 3/8" regulator, but I can't right now. I just went out and looked through the brass I have left over from that install still in its little plastic bags, but I don't have that exact one; the closest thing I have NIB is a ½" x ¼" bushing, which is in their "Watts" product line, part # A-827.

Talk to some old guy working there that looks like he's been around the block a time or 2, not the fabulous teen-age babe, it's in there, all they have to do is point you to it. When you see it you'll know exactly what I'm talking about.

 

I am Adam's cousin. I went over to his house today and looked at his car. I didn't see this topic untill afterward, but what I did to fix it for him was go to a home care place like Home Depot (but wasn't Home Depot) and got a 1/2 inner to 3/8 outer thread adapter for home gas lines. It worked like a charm, only problem he had was that the wire popped off the sender once and touched the manifold...so the black shield stuff we had put over the wire melted a little from touching... he doesn't have an end with ears to hook on so we made due.... I suggested he look for a wire that will lock on to the sender, I'm not a big Chevy guy so I don't know if there is one.

 

Yup, that about sums it up.

Still one problem though... the fan now *sometimes* works, but about 3/4 of the time, it will not turn on at all and i still have to manually turn it on with the AC!

The first time this happened, it was only because the wire came disconnected, but that has only happened one time. Every other time it just seemed to not wanna work. Other than the heat shield wrap being a little melted (not from touching the manifold, just a little too close) everything appears to be fine. The connector (bullet type) looks fine to me, and i've been around these things long enough to know, and as far as i can tell, has a good, tight connection with the wire and a solid fit onto the switch as well.

Any ideas on whats going on? I don't think the switch is a dud because it does work every now and then, and does bring it down to the right temperature, (me and Karm have been driving it all day today) but only works about 1/4 of the time.

Whats up with this thing?

 

Anyone?