Replacement/Installation of a Thermostat

APPLICATION: All Volkswagen vans with air-cooled Type 4 engines. Those are all Volkswagen vans from 1972-1983 (except, of course, for 1982 and 1983 Vanagon diesels and 1983 water-cooled Vanagons).

TOOLS NEEDED: A couple large screwdrivers (phillips & flat-head); a 9mm open-end wrench; a 10mm wrench and socket with ratchet; 13mm wrench or socket.

This procedure is for those who are replacing their existing thermostat and those who are installing a thermostat from scratch. If you don't have a thermostat, get one!

We'll start with replacing your existing thermostat. We will assume that everything is hooked up and operating properly except that the thermostat itself is bad. We will go through the steps to replace it.

TROUBLESHOOTING: How do you know if the thermostat is bad? The simple answer to this question is to look at it. If it's bad, it will be expanded and will act like a big spring when you squeeze it together. Another indication is if the air control flaps (that the thermostat controls via cable) never move from their full-open positions. This can be checked by observing where the thermostat cable connects to the rod that the flaps connect to. Look in the engine compartment, just forward (front is front) of the fan housing. You will see a cable coming up through the engine tin and attaching to a rod. There is a little vertical protrusion where the cable attaches. If the protrusion is fully vertical, then the flaps are open completely. If it is pointing toward the front of the van, the flaps are closed. If the flaps are open but the engine is cold, check out the thermostat. Either it's bad or the cable is broken or it's way out of adjustment.

OK, so you've determined the thermostat is bad or you at least want to have a look at it. You can find the thermostat by crawling under the engine with your large screwdrivers (and maybe the 10mm wrench) and removing the under-cylinder tin under the right side of the engine. There are a few screws (or bolts, depending on your previous owner) holding this tin to the engine case, some other tin, and the heat exchanger. Find these screws and/or bolts (my '81 has both) and remove them. Watch out or the tin will drop on your forehead. It doesn't hurt too much but it's usually greasy and you don't want that in your hair.

Once the tin is out of the way, you are looking up at your pushrod tubes and cylinders. You should see there below the pushrod tubes toward the front of the engine (front is front) a bracket bolted to the case with a bellows-looking thing in it. That's your thermostat. Do the squeeze test on the thermostat now. If it squeezes together with little resistance and bounces back when you let go, it's bad. Get a new one from your FLVWAPS (I once went to a regular auto parts store and they handed me a thermostat for a water-cooled car. Didn't believe me when I told them that wasn't it, either). It should cost around $18. Yes, $18! But you need it so you have to pay it.

If your thermostat turns out not to be bad, then your problem lies elsewhere. But here we're talking about how to replace the thermostat.

OK, you've got your new thermostat. Now you've got to remove the old one. First step is to unscrew the cable from the old thermostat. There is a large nut that fits over the cable and threads onto the thermostat. This nut is 9mm. Get your wrench on it and remove this nut. If the cable is attached to the air control flaps rod, it will just hang there, so let it be.

Now you have to free the thermostat from the bracket. On the front side (front is front) of the thermostat there is a 13mm bolt that holds the thermostat to the bracket. Undo this bolt. Depending on how rusty and crusty your thermostat is, this bolt really may not want to come off. In that case, undo the two 10mm bolts that hold the bracket to the case, remove the bracket with thermostat still attached, put the whole schmutz in a vise and use your favorite bolt-loosening techniques to remove it. Liquid wrench and heat probably go a long way.

OK, so however you've done it, the thermostat is out of the bracket. Notice that when the bolt comes out, you also have a regular round washer and a rectangular spacer. Don't lose the spacer! You will need it later. Try not to lose the washer either :-)

While your thermostat is disconnected, take this opportunity to inspect your air control flaps. Work the actuator rod back and forth with your finger. Ensure they work smoothly throughout their travel. If they don't you will need to find some way of lubricating them. You will notice that as the rod passes into the engine tin on each side, there is a small plastic bushing that the rod rotates in. This is where you need to lubricate. The real fix for this is to remove the fan housing and clean everything up and lube well, but that's kind of a big project for the novice. If you can find a way to lubricate the rod in the bushings, go for it. Otherwise, you may want to wire the flaps open as you don't want them to bind in a closed position. Please note I only recommend this as a temporary fix until you have the time to pull the fan housing and fix it properly.

Another thing to inspect is the fail-safe spring. You will notice that wound around the flaps actuator rod on the right side is a spring, with one end resting under a lip on the fan housing. This spring's sole purpose in life is to force the flaps into a full-open position if the thermostat cable breaks, or the thermostat fails, or is disconnected. Make sure it does what it's supposed to do. It's very important. If this spring is broken or missing, the thermostat will expand just fine but the flaps will not open and will overheat your engine badly.

OK, so moving on, you now have everything working properly and greased up. OK, let's put the new thermostat in. If you removed the bracket, bolt it to the case now. Next, insert the thermostat into the bracket. Notice that one end of the thermostat is threaded and the other has an oval protrusion. Notice also that the bracket has an oval hole on one end. Fit the rectangular spacer between the bottom (oval part) of the thermostat and the bracket, then put the thermostat in the bracket, and make sure you get the oval protrusion into the oval hole in the bracket. Once you've got that, then insert the 13mm bolt and washer into the thermostat and tighten it down.

Next step is attaching the cable. Take the cable end and thread it onto the thermostat the same way it came off. Make sure the cable is routed properly, i.e. it goes through the pulley that is bolted to the case. Tighten the cable to the thermostat with the 9mm wrench. Since the thermostat is at room temperature and is contracted fully, it helps here to have someone in the engine compartment pushing on the flaps actuator rod so the cable will reach to the contracted thermostat.

Once you've got that, you want to check the adjustment. Ideally the flaps should be fully closed when cold (push on the flaps actuator rod to verify) and fully open when hot (pull on the rod to verify). If you can't get it like this, better to have it fully open when hot and partially closed when cold than the other way around. The adjustment can be made at either end. You can loosen the two bolts that hold the bracket to the case and move the bracket back and forth or you can loosen the 7mm bolt that holds the cable to the flaps actuating rod and adjust it there. I hope I've mad this clear. Once you think you've got it, replace the under-cylinder tin and go for a drive to get it nice and warm. Check the position of the vertical protrusion on the flaps actuating rod (where the cable connects). If the flaps are fully open, it will be standing vertical. You can check it by pulling it to the rear of the van. If you can pull it back more, it was not fully open. Adjust as necessary.

Now, if you're installing the thermostat from scratch, you will need to know what parts you need. You need: Thermostat bracket
Cable end
Two bolts and washers to hold bracket to crankcase
One bolt and washer to hold thermostat to bracket
Rectangular spacer

As far as I know, the bracket is still available from the dealer for about $11, and I think most of the other parts are available too. You may be able to find good used parts at a junkyard for cheap.

Once you get all the parts together, just follow the instructions above to install them.

Sean Bartnik
November 30, 1997

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