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[GMCnet] Olds 455 Engine Oil Flow Path [message #211273] Sun, 16 June 2013 13:49 Go to previous message
USAussie is currently offline  USAussie   United States
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma:
Senior Member
G'day,

There has been much speculation regarding the recommendation not use the oil cooler in the radiator after an engine failure. It is
the intent of this email to review the engine oil flow path to form a consensus if that is correct or not.

This message was prepared by John Sharpe and myself.

Oil Flow Path in a 455 / 403 powered GMC Motorhome

Below is a picture of the inside of the oil cooler / filter adapter.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49551-oil-cooler-filter-ad.html

There are three “ports’ in the concave center section; from right to left they are:

1) oil entry port from the engine oil pump
2) oil cooler adapter mount and oil return to the engine
3) 5.3 to 6.3 psi bypass valve and return to engine

The distance from the center of the oil entry port to the center of the bypass valve is about 1 ¼ inches.

The oil flow path is as follows:

From the oil pump into the concave section of the oil cooler / filter adapter through the port on the right.

From the concave section of the oil cooler / filter adapter to the oil cooler adapter.

From the oil cooler adapter through a hose / tube to the oil cooler in the radiator.

Through the oil cooler in the radiator.

From the oil cooler in the radiator back through a hose / tube to the oil cooler adapter.

From the oil cooler adapter to the OD of the oil filter (outside the filter element).

From the OD of the oil filter to the ID of the oil filter (through the filter element).

From the oil filter into the engine through the center port in the oil filter adapter.

Below is a picture of the interface between the engine block and the oil cooler / filter adapter.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49548-block-oil-cooler-fil.html

Oil enters the oil cooler / filter adapter via the upper port and back into to the engine via the lower port. The lower port has two
feeds; one from the oil filter the second; the bypass valve.

Below is a picture of the oil cooler / filter adapter with the bypass valve removed. Note the “poppet guides” at 12:00 – 4:00 –
8:00. Using deep well sockets I measured the ID of those guides and found that they tapered inwards as the bore got deeper. At the
top the ID was 0.576 inches, in the middle the ID was 0.558 inches, and at the bottom it was 0.543 inches.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49549-bypass-poppet-removed.html

Below is a picture of the bypass valve seat, poppet, and spring.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49550-bypass-poppet.html

If you look closely at the poppet you will see one flat area (at about 2:00). The fit of the poppet in between the three guides left
a bit to be desired as it varied from 0.533 to 0.517 inches OD (where the flat spot was).

Below you will find the oil flow schematic and write up for the 455 / 403 engine as found in the Maintenance Manual (MM).

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49554-engine-lubricating-system.html

MM write up below:

Oil enters the pump through a screened inlet located near the bottom rear of the oil pan. The pressurized oil from the pump passes
through the engine oil cooler located in the radiator tank then to the oil filter located on the right rear side of the engine
block, see Figure 2. The oil filter base has a by-pass valve which in the event of filter restriction will open at 5.3 to 6.3 psi.
It then enters the right gallery where it is distributed to the five main bearings. The right bank valve lifters receive oil from
this gallery from eight feed holes that intersect the gallery.

The line drawing below of the oil flow external to the engine can be found in the MM.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49555-external-oil-path.html

As a guesstimate the total length of the hoses to / from the engine is 9 feet.

The line drawing of the oil filter / cooler adapter / filter below can be found in the MM.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49558-oil-cooled-filter-adapter.html

As a guesstimate the oil cooler adapter is 1 1/4 inches tall.

Below is a picture of the screen in the oil pump pickup.

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49557-oil-pump-intake-screen.html

Using a numbered drill we determined that the size of the “square holes” in the screen were 0.055 inches in width and height. With
the help of Pythagoras the corner to corner measurement of the “square holes” was calculated to be 0.077 inches. Therefore in theory
the largest size particle that can enter the oil pump is 0.077 inches. Yes, I realize a sliver that was less than that in width and
height could be longer, however it would have to pass through the screen lengthwise.

Given all the information above we believe the cold oil bypass flow path to be:

1) engine starter turns the engine / distributor / oil pump

2) oil is sucked through the screen and into the oil pump

3) oil is pumped into the concave area of the oil cooler / filter adapter

4) oil is thick and the pressure differential across the bypass valve exceeds 5.3 to 6.3 psi

5) the bypass valve opens and oil is returned to the engine

Why would the oil take the following flow path?

1) from the oil cooler / filter adapter to the oil cooler adapter

2) through 4 ½ feet of hose to the radiator cooler

3) through the radiator oil cooler

4) back through 4 ½ feet of hose

5) into the oil cooler adapter

6) Into the oil cooler / filter adapter

7) Through the bypass valve

Instead of the 1 ¼ inches from the inlet to the bypass valve in the concave area in the oil cooler / filter adapter!

Comments / observations please.

Now lets move on to the recommendation to cease use of the radiator oil cooler after an engine failure.

Below is a photograph of a failed piston:

http://www.gmcmhphotos.com/photos/455-403-engine-oil-flow-path/p49556-failed-piston.html

How much contamination would you guesstimate this failure generated? An ounce or two?

Let’s say that the owner of this GMC continued to drive the GMC and ignore the noise the engine made (he did not) and it lead to the
top of the piston fracturing. That would create another couple of ounces – MAYBE.

Let’s say the owner was a complete idiot (he is not) and kept driving until the bearing on the rod this piston was attached to
failed. That would add an ounce or so to the contamination.

I reckon as a worst case scenario you might get 6 ounces of contamination in the oil cooler from a catastrophic engine failure.

Comments / observations please.

Finally let’s discuss the cleaning of the radiator oil cooler.

Let’s say the engine failure puts 6 ounces of contamination into the oil pan. It has to get past the screen in the oil pump pickup
so the largest particles will be 0.0777 inches in size.

Let’s say that all 6 ounces makes it to the oil cooler in the radiator and should be cleaned out.

Someone suggested a pump setup that would pump a high flow of “cleaning solution” backwards through the oil cooler. That makes sense
to me. It should be setup so that you can capture the contamination after it is removed so the amount can be determined and the
makeup determined from a material stand point which would help determine where it came from.

Here’s the punch line – even if you don’t get all of the contamination out of the oil cooler the oil filter will catch it during
normal operation of the engine!

As noted previously engine oil is bypassed BEFORE it gets to the oil cooler / filter adapter meaning the contamination that is not
trapped by the filter can’t get into the engine!

Comments / observations please!

Regards,
Rob M.
Sydney, Australia

JohnS
Humble, Texas

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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