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Old 05-05-2009, 04:41 PM
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Pontiac oil pressure sending unit question

Hey guys I'm working on my '79 Trans Am with a pontiac 400 and I'm having trouble getting the oil pressure sending unit to fit properly. The stock one is rather "fat" and keeps hitting on the bellhousing before I can get it to tighten up. There really isn't much room back there between the bellhousing and dizzy. Does anyone know if I could use a narrower one or know a part # I could try? Thanks.

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Old 05-05-2009, 06:51 PM
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I hit a similar problem on 70s chevy, I think I had firewall clearance issues. I bought a little brass after market one, only about an inch high, and as big arond as a sharpie. But it wasn't electronical, just ran the line to my oil pressure tach in my car. If thats all you need save money and hit the brass connectors at a Menards first .

But it sounds like you want one with a wire hookup . . . my buddy had a pontiac with a Y type sending unit, I know he couldn't get it to fit , it had sensors on a brass fitting. He ended up buying an aftermarket one as well, don't remember the name, but it was shorter and very fat with one wire hook up. I don't know about thinner ones if you need an electrical one.
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Old 05-05-2009, 07:26 PM
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Quote:
Originally Posted by muzzfactor
I'm having trouble getting the oil pressure sending unit to fit properly.
What you'll need to do, is use a pipe "nipple" to thread into the block w/another (possibly angled) fitting atop that with female threads to fit the sender.

Your sender is designed that way (fat) because you have a gage and not an idiot light.
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Old 05-05-2009, 07:48 PM
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Really I always assume fat = light, thin=gauge. Perhaps it is the difference in what we each use, I've alwas seen short, fat little wire hook ups, and thin brass fittings, not vice a versa. If it is a 79 though should have a "idiot light" stock. I posted some pics of what we are talking about, as far as the fittings and nipples goes you can pretty much find any size/shape you want and or need.
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Old 10-11-2013, 07:26 PM
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Interference with oil filter

I have a 75 TA 400 6.6 with gauges and have the large oil sending unit that
cannot be tightened completely and seeps oil out the gasket as the outer edge of the sending unit is riding on the top of the oil filter.

I don't know if the GM oil sending unit for gauges is narrower but it seems that GM designed this a little better.

Can anyone give me some guidance on fixing this?
thanks,
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Old 10-12-2013, 02:54 AM
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Using an angled fitting having 1/4-18 NPT (pipe threads) will allow the sender to clear the filter, as shown below (from here):



Another option is to plug the filter housing sender hole and use the tapped pipe plug hole up on the top rear of the engine. This is sometimes done when extra clearance is needed.

Remember the pressure sender is a pipe thread, so be sure to not overtighten. Sealer is sometimes used; it's usually not a good idea to use teflon tape to seal the threads, though.

Last edited by cobalt327; 10-12-2013 at 03:17 AM.
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Old 10-12-2013, 05:19 AM
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Clarirfication

Quote:
Originally Posted by cobalt327 View Post
Using an angled fitting having 1/4-18 NPT (pipe threads) will allow the sender to clear the filter...
I can't recall now if the threads are 1/4 or 1/8 so check first.

Quote:
Another option is to plug the filter housing sender hole and use the tapped pipe plug hole up on the top rear of the engine. This is sometimes done when extra clearance is needed.
Or if a remote filter is used.

Quote:
Remember the pressure sender is a pipe thread, so be sure to not overtighten. Sealer is sometimes used; it's usually not a good idea to use teflon tape to seal the threads, though.
There's no actual flow at the sender, so in theory there shouldn't be a problem using teflon tape, but it's generally just a good practice to keep teflon tape away from automotive fluid systems due to the possibility of the filaments formed when a taped joint is disassembled entering the system on reassembly. Even if one is careful to clean the male and female threads, often some gets missed. Much safer to just use a liquid/paste sealer made for the purpose and leave teflon tape to plumbers/pipe fitters.
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Old 10-17-2013, 09:30 AM
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The threads are 1/8-NPT.

The stock sender just screws directly into the filter housing. It should be a "can" about 1 1/4" in diameter and about 2" long, with the pipe threads on one end, the bayonet for the plug on the other.

We use the tap-hole near the distrubtor for more accurate readings as to what is actually going on INSIDE. Rather than at the beginning of the "stream", it's down-river a ways, and will be more realistic.

Teflon tape seems to deteriorate when it contacts oil. We've found it in pump screens AND filter elements. (bad) We use Permatex "Aviation" to seal all threads in an engine.

While you have the housing "off", remove the bypass valve (1/4" headed screw, "paddle", spring and puck). Tap the hole for 3/8-NPT and block the bypass with a steel pipe plug. We do this to EVERY Pontiac we build, regardless of "level". Adding the gallery plug with a .030" hole in it "behind" the distributor helps there, too (provides POSITIVE lube to a known wear point).

Jim
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Old 10-17-2013, 11:52 AM
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If you plug the oil by-pass in the oil filter adapter, you better use a high flow filter and change it every 1,000 miles and never spin the motor over 5,000 RPM.

The by-pass valve with the stock by-pass spring begins to open at 3,500 RPM and is fully open at 5,000 RPM. It is designed that way because the oil filter will not flow enough oil to properly feed the bearings above 5,000 RPM. . The oil filter by-pass valve is a safety device in case the oil filter gets clogged or the filter fails to flow enough oil at high RPM. The oil filter by-pass will save the motor if you over-rev the engine...... I had rather my engine run on unfiltered oil than no oil at all.

I plugged the oil filter by-pass valves in my '69 Firebird 400 and '66 GTO until the Lee two-stage (filtered by-pass) filters were discontinued in 1980. The Lee two-stage filters had a low restriction-high flow filtered by-pass section of the filter media that would still flow a adequate amount of oil if the engine RPM exceeded the flow capacity of filter. If you block the by-pass,use a WIX Racing 51060R oil filter. Media rated at 31 micron filtration and 28 GPH flow rate. The WIX 31 micron filtration rate is for higher flow and it will still catch some of the bigger chunks. Change the oil and filter every 1,000 miles.

Last edited by MouseFink; 10-17-2013 at 12:19 PM.
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Old 10-17-2013, 06:25 PM
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I plugged the bypasses in several Pontiac engines (and every Chevy engine I've built since the mid '70s) including my own and have had exactly zero issues. And they got- and some are still getting- the hell ran out of them. Use an oil pressure gauge- it'll show if the filter is plugging up by a drop in oil pressure. But I didn't ever see a drop between 3000 mile oil changes. I would submit that if the filter is plugging up w/debris after 1000 miles, you have a lot more to worry about than the bypass being plugged!
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Old 10-17-2013, 06:47 PM
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ok guys this thread is from 09 and the OP never responded !
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Old 10-17-2013, 09:28 PM
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It was revived at post #5...
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Old 10-18-2013, 06:25 AM
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I just discovered that WIX does not make a racing oil filter for a Pontiac engine, why should they? If the by-pass on a Pontiac engine is blocked, I don't know which filter is recommended.

AC Delco filters today are worthless and begin to restrict flow above 3,500 RPM. Champion Labs makes a good high flow AC Delco UPF52 Ultraguard Gold fiter for LS Chevrolets and Cadillac CTS-V racing. I bought 60 AC Delco UPF52 Ultraguard filters so I will have a good supply before they are discontinued. They are not cheap with a price range from $9 to $21 each.

The by-pass is needed because GM filters do not have a built in filter by-pass. A Chevy 21 PSID (differential pressure) by-pass is in the block and a BB Chevy by-pass opens at 31 PSID. The only filter by-pass a Pontiac engine has in in the oil filter adapter so think about that before you plug it.
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Old 10-20-2013, 08:13 AM
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Mousefink,

I have no idea where you get your information, but the idea of RPM-related bypass is COMPLETELY erroneous. It is controlled by the amount of oil pressure against it. The theory being, if/when the filter "clogs", pressure build-up pushes the bypass open, allowing the engine to oil. The Pontiac is notorious for allowing unfiltered oil through as low as 35 lbs (normal oil pressure above 2,000 is 60 lbs). We've (Pontiac builders) been blocking the bypass since the "beginning of time". If one uses a quality filter of any brand, it is fine. We (CVMS) will not warranty and engine with an "orange" filter. Wix, NAPA (Wix relabeled), Purolator, A/C have all proven to be 100% reliable over the last 25 years.

It's funny (ironic), but what some of us "do" is completely different than the assumed procedure. Following is a "list" of Pontiacs revving beyond 6,500 RPM with blocked bypasses... (minimum of 50 passes on the same short block)

Gallopin' Goat ('68 GTO, all-steel, 462 CID, 9.88 @ 134, d-ports, shifts at 7,500)
Jolly Green II (434 CID, 3,400 lb. '65 GTO ragtop 4-speed, shifts at 7,000, 10.31 @ 130)
Pinball Dan's '69 Firebird (3,810 lbs. "race weight" [Dan's a big boy], 11.17 @124, 461, 89 octane, 6,600 RPM shifts)

There are many more. These, you can "verify" through a search if you feel the need.

Every Pontiac we build, stock or other, gets the bypass blocked. I personally built and "shipped" 27 Pontiac V8s last year (2012).

FWIW

Jim
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Old 10-20-2013, 08:37 AM
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Oil pressure is determined by the RPM. The oil by-pass is designed to open about 3,500 RPM and at 15 PSID (differential) oil pressure. The by-pass is fully open when the engine reaches 4,000 RPM. If it is so great to block the oil supply to the rod and main bearings at high RPM, why did the Pontiac engieers put a oil filter by-pass in the oil filter adapter? It is not a problem to install a stronger by-pass spring and raise the differential pressure to 20-25 PSID but it is foolish to completely eliminate the oil filter by-pass, especially in a Pontiac engine that does not have a by-pass in the engine block.

GM oil filters that are designed to be used used in engine blocks that are equipped with a by-pass do not have a by-pass. The engineers put oil filter by-pass in the engine block (or in the oil filter adapter) , because oil filters cannot flow enough oil to adequately supply the bearings at high RPM. BB Chevy marine engines have a 31 PSID oil filter by-pass. Why would anyone want to completely block off the oil filter by-pass in any engine?

Last edited by MouseFink; 10-20-2013 at 08:59 AM.
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