The small block (302/351W) is a "fun" engine to change the 'stat on. That's because some engineer with a sense of sadism decided the 'stat should sit vertically between the intake and the housing.

In my experience, I've had to buy the gasket separate from the 'stat, and I always use a self-adhesived gasket. Always. That's because you have to use the gasket to keep the 'stat in the housing while you put the housing against the intake manifold.

Further, I always use a bit of sealant on the BACKSIDE of the gasket. I hope you got the "backside" hint because any sealant put on the adhesive seems to ensure the gasket will not stick and the 'stat will fall out of the housing. Don't ask. Anyway, put the 'stat nestled in the housing's depression with the copper bit sticking out and put the gasket's sticky side against it. And make sure the 'stat doesn't shift and get out of the depression. Don't ask. Then, put a bit of sealant on the backside of the gasket, put the contraption against the manifold, and insert the bolts.

HOWEVER, make absolutely sure you pay attention to which bolt goes where as one is longer than the other, at least on a 351W, and if you swap them you WILL have a leak. Don't ask. If you put the longer bolt in the short side it won't pull the housing up to the manifold, causing the leak.

Having said all of that, there is another type of housing that requires a different 'stat, one that isn't a full circle. The housing has slots that the wings of the 'stat go into and then you turn it and it is locked into the housing. These don't require the adhesived gasket, but it doesn't hurt. I'm not sure which engines these came on but know they are out there.

 

Thank you Gary, for the excellent description. I am wrestling with the ICVR possibility this morning before proceeding to replace the thermostat, temp gauge sending unit, and radiator cap. Again, thank you for the help.

 

Yes. The copper of the printed circut can turn brown and oxidize over time. You can clean the copper with a block pencil eraser. You will have to completely dismantle the instrument cluster to do this though. Not too difficult.

You can apply a small amount of dielectric grease to protect the copper from oxidizing again. Just becareful and don't scrub too hard with the eraser as the copper is just "foil" stuck to the printed circut and can be damaged by over "aggressiveness".

May not eliminate your problem, but if you are going to replace the ICVR anyway, would be good preventative measures.

This will work if the cluster connector where it connects to the instrument cluster is loose. When you hit a bump it loses ground etc... Would not fix a defective ICVR though.

This ground is on the left side of the engine compartment. Look directly below where the speedometer cable exits the cab on the firewall. Look for a cable or a mounting hole in the firewall. If it's bad or missing you can replace this ground with a battery cable of the correct length from most autopart stores.

Also check the negative battery cable to engine block ground, (V8 engines) or the negative battery cable - to frame - to starter mounting bolt cable, (Inline-six engines) as these need to be clean and tight for the engine to cab ground to be effective.

There is also a ground wire below and to the right of the radio that grounds to the dash support frame. Look for a black wire or wires attached to the support metal with a hex headed screw. You would need to remove the radio to see this ground.

Also there are lower support brackets for the dash assymbly. Remove one of them, clean the metal where it attaches to the firewall on one side, and on the otherside where it attaches to the dash metal assymbly.

Then you can clean any component, such as the underdash courtesy lamp housings for example, that bolt directly to the dash support for ground etc...

That should take care of any ground issues to the dash metal support.

Usually though, the ICVR will stick causing this problem. The ICVR gives off voltage in pulses to regulate the voltage flow. When it sticks it alows full voltage to the gauges, pegging them. Why hitting the top of the dash seems to work. It "unsticks" it for awhile. A bad ground can cause the ICVR to stick but not as comon.

Still cleaning the grounds is a good idea.

 

81F -
Appreciate the detailed response. Working on it now. Have to go slowly since I don't have parts to replace anything I break. Will post back with more later. Thank you.

 

Gents -
I removed the instrument cluster, removed the ICVR, cleaned the part of the bracket on the ICVR that contacts the copper coating on the printed circuit, cleaned the corresponding part on the printed circuit, even took the ICVR apart and very cautiously cleaned the contacts that open/close. Reassembled the ICVR, mounted it back on the instrument cluster, re-hooked the ribbon cable to the back of the instrument cluster, turned the key, and was disappointed to see the fuel gauge needle peg to the right. I started the truck and now the oil pressure needle also seems to be further right than normal (however the truck was cold and the oil pressure will usually read higher right after I start the truck). Bottom line is the problem is still with us so apparently ICVR replacement is necessary. I found an ICVR on Ebay for $37.50 shipped but unfortunately do not have an Ebay account. Went to Autozone, Advance, & O'Reilly's but they did not have the part and could not get it (AZ & O'R). So, do any of you know a source for a replacement ICVR? I can use the truck "as is" but surely putting 12 volts into gauges that are supposed to be getting about 5 volts will eventually destroy the gauges. Any help appreciated.

 

I found a Motorcraft GR513 at a high price but went ahead and ordered it. Thanks for all the good help.

 

Can you cancel the order? I have several instrument clusters and they all have IVCR's.

 

Motorcraft GR513 is the correct one. I would get it used from Gary or someone else if I could though.

The ICVR is very delicate inside. Never thought to advise you not to open it to clean it.

 

We have it covered, with the exception of tomorrow being the Saturday before Sunday. (I'm retired and have 6 Saturdays and the only problem is figuring out which is the one before Sunday.) On that Saturday, IIRC, the Post Office is closed. Right?

 

My post office is closed tomorrow and Sunday, so yes...

 

Sorry, Tomboy, it'll go out Monday.

 

A sincere thank you to Mr. Gary Lewis for his kindness and courtesy. After post #35, I went outside to gather my tools and close up the truck. Imagine my surprise to see the ground screw for the ICVR laying on the front seat of the truck where I put it to be sure I did not forget it! I installed the ground screw on the ICVR, started the truck, and the gas gauge needle stopped at the full mark rather than pegging the needle all the way right. I was encouraged and hoped maybe the cleaning of the IVCVR mount and corresponding surface on the printed circuit had helped. This morning we rode about 45 miles in the truck (mostly interstate) and the temp gauge needle stayed slightly left of center without fluctuation. I am pleased but will reserve judgment until I do more test driving tomorrow. Sure do want to thank Gary Lewis again for the part and the other forum members who have offered help. Tomboy

 

Congrat's! Yes, that screw would make a big diff. You were putting full battery voltage, about 14.4, to the gauges instead of 5.5 volts. But, just in case you don't like where it is reading you'll have a couple of other choices.

 

Oh yes, that ground screw is essential for the ICVR to work.

Keep us informed on how everything is working.

Hopefully you got your problems solved.

 

I believe the fluctuating temp problem is now solved. After catching and correcting my mistake of failing to re-insert the ICVR retaining/grounding screw when I reinstalled the ICVR day before yesterday, I drove the truck about 45 miles yesterday and about 90 miles today. The temp gauge needle stayed slightly left of center the entire time for both days. This slight left of center position is where the temp gauge needle has been for the last 26 years during normal operation when the truck was running well. The gas gauge has also seemed to normalize. Based on where the gas gauge needle was reading when I stopped for gas on the way home today, I estimated there was six gallons left in the 19 gallon tank so expected to buy about 13 gallons. The tank held 13.359 gallons so it seems the temp and gas gauges are now giving reliable readings. I am still confounded that this gauge fluctuation problem was caused by the light coating of oxidation I removed from the mounting tab of the ICVR and on the corresponding copper of the printed circuit. Minor culprit, major problem. Thank you again for the helpful comments. Be safe. Tomboy