Rythmic knock sound

[500hpgtx]

Hi TS guys!!

95 Transport 3.8L

My wife hammered me about our TS sounding loud. An exhaust seal was replaced before the Cat converter, and she still complained. Unfortunately, she is always right about problems with her van.

Once this van gets very warmed up, there is a low grade, soft, knocking sound, that increases with increased rpms from the engine , while in gear.

WHen I was first hearing this, I was thinking a main bearing knock, due to 160K miles. The engine oil was down due to a previous leak, and I added heavier 20/40 oil. The oil pressure gauge indicated around 25lbs, prior to adding the oil. At this point, when warmed up, it is around 30-35 lbs and increases with engine rpm. JRS3800 has told me prior that the gauges are flaky on our vans.
I recently serviced the trans and added Lucas trans conditioner with the idea of possibly eliminating this noise. I am not certain if this noise is related only to the trans. With the trans in gear(under an engine load) the mild knocking increases with engine rpm. It may become more aparant when moving.
I have tried to isolate this noise, and it appears to be around the flex plate/converter area. Has anyone experienced a rythmic , soft , knocking sound from a trans issue?
Anyway, I had fun irritating my wife y telling her to "turn the radio up a little". Have a great Christmas Guys!!

[500hpgtx]

Unfortunately, I think a main bearing is going out. When the van is in gear, it is under a load. I am going to put a couple quarts of lucas engine stabilizer and heavier oil and see how long the engine will last. 170K miles and years of hauling kids back and forth is a lot for any vehicle. Cheers!

[Jrs3800]

Kev,

I know I am way late to this thread, But did you ever get this figured out?

As well its ironic, my original engine in the van went out at about 180,000 miles.. I ran it 3000 more miles with 20-50( horrible to do to a 3800 ) but it was on its way out... Gave me enough time to figure out what to do with it... Its had a series III with series II induction for the last 5 years now... Just started have knock sensor circuit issues..

As well iirc you have a 95, and as such it should have that freaky series I 3800 with the series II crank...

Also to note, sometimes the balancer can go bad and create a sound that sounds just like a rod knock...

Sorry I'm so late to this thread..

[500hpgtx]

Thought you were gone JRS3800!!;-)

Engine sound is probably classic of main bearing failure. The engine is fairly quiet when cold. Of course I am using a quart of lucas engine treatment and I am running 20W 40 W. Our van has 170K miles. Synthetic blend has always been used. When the engine is warmed up , it has a rythmic thump like sound with a low pitch. I believe it is getting a little louder with time.

The harmonic balancer was replaced several years ago. It failed abruptly and produced a violent shake in the engine bay.

After replacing the upper and lower intakes, I really do not know if I want to deal with any more heavy work on this van. My body and spine suffered for several months as a result of the hours bent over the hood on that job.(spinal damage and arthritis)

I will likely use 2 quarts of lucas oil stabilizer and another 3 quarts of 20w 50w next oil change. I have a patient that was a mechanic for Orland Park for years. He agrees that it is likely main bearing failure. However, he said he has known cars that have been driven for a number of years like that!

Good to hear from you JRS3800(Don)!!

[500hpgtx]

The sound from the engine is close to this youtube video.

https://www.youtube.com/watch?v=zeV0TLfpDlE

[Jrs3800]

I know exactly what sound you are trying to relay... I heard a ton of those 4.1,4.5 and 4.9's do that back in the day...

The 3800 Tuned Port L27 had problems with the main bearing clearances and in some cases the mains would wear and create too much clearance, seemed to be a problem with the #1 main more so than the others.... The 3300 from 89-93 also suffered this problem.. supposedly GM had corrected the problem but it really seems to be hit or miss.. Some would live to near 200k and other were still prefect at 300k... So you just never know..

Mine on a cold start had a tap until the oil came up to pressure.. But it survived like a trooper.. I still have that original freak year 95 motor and plan on rebuilding it for use in another car..

almost 20 years tho, its been a good van and a good motor.. I can't say anything bad about yours or mine..

and there is that saying, My GM car will run badly longer than your car will run at all...lol

[500hpgtx]

With advancement of synthetic oils today, I think I may extend the life of the main bearings by using 3 quarts of 20-50 synthetic or blend plus 2 quarts of lucas synthetic oil stabilizer.
With cold oil pressure around 50-60psi, it is amazing how quiet it is. I am obviously looking to kee p the pressure around 40 psi when hot. With a worn 3800, I think the engine can only benefit from the added viscosity. Since I am not revving the engine on a regular basis, I think the oil flow restrictions from the increased viscosity should not be a problem...Reminds me of the 70's using Motor Honey..cheers

[LMP]

Glad to hear you guys.....even if the topic sound alarming....but it keeps some life in this forum in which silence has become the norm.....
In a few weeks I'll have my '93 back on the road....this after being hit form the rear last september. It has saved the car from winter salt....and I have been able to make what I think the best out of the situation. Some trace will be apparent but overall most will not notice it....will post a few photos soon.
Keep them rolling....

Hey..what happens? When I open the forum I get this message at the top and sometimes it does not allow me to access the thread....
www.avigex.ca/xport/AFmessage.txt

[WelmoedJ]

Originally Posted by 500hpgtx

With advancement of synthetic oils today, I think I may extend the life of the main bearings by using 3 quarts of 20-50 synthetic or blend plus 2 quarts of lucas synthetic oil stabilizer.
With cold oil pressure around 50-60psi, it is amazing how quiet it is. I am obviously looking to kee p the pressure around 40 psi when hot. With a worn 3800, I think the engine can only benefit from the added viscosity. Since I am not revving the engine on a regular basis, I think the oil flow restrictions from the increased viscosity should not be a problem...Reminds me of the 70's using Motor Honey..cheers

If I am correctly informed, it's not a good idea to start using full synthetic motor oil in an old engine.

The Pontiac uses half-synthetic motor oil and because the engine has been using this type of motor oil for a long time the "cure" may cause all kinds of new trouble.
Full synthetic oil is supposed to keep the engine cleaner and may also clean old "dirt" inside, causing blocking of oil channels and other issues.

Only after a full engine overhaul (meaning a totally cleaned engine) you can start using full synthetic oil.
We've experimented with a 32 year overhauled engine (alike the Pontiac injection system, not carburetted) and this car and engine still runs fine.

Using an oil conditioner is not one of my favorites for the same reason as starting using full synthetic oil to replace other oil types.

My 2 cents.

[500hpgtx]

Interesting point Welomoed J. I have been using synthetic blend since this van was new. When I took the intake manifold off, I was surprised that there was a moderate amount of sludge in the lifter and balance shaft area.
I have never run full synthetic, but I already have leaking from the rear valve cover area. I am trying to avoid replacing any gaskets as my back does not need the aggravation. (being 6'3+)

What is interesting is that my 3800 sries 2 L67 in my grand prix is absolutely clean. I have been using full synthetic since day 1. When I pulled the intake to put on an intercooler some years back, I was impressed how clean it was.

A guy with an L67 supercharged said he was looking for a replacement engine for his 97 GTP. He said he had 355,000 miles on his original engine.

[WelmoedJ]

Originally Posted by 500hpgtx

Interesting point Welomoed J. I have been using synthetic blend since this van was new. When I took the intake manifold off, I was surprised that there was a moderate amount of sludge in the lifter and balance shaft area.

Though I presume the Canadian and US owners drive longer distances than we, owners in Europe, I also noticed some sludge. However with 255k kilometers (some 159k Miles) and city as well as highway driving I expected that.

Originally Posted by 500hpgtx

I have never run full synthetic, but I already have leaking from the rear valve cover area. I am trying to avoid replacing any gaskets as my back does not need the aggravation. (being 6'3+)

I used the term "full synthetic" as this is usually used by the salesmen to differentiate from other oil types.
FYI: I'm 71 and before the PT 3800L died on me I have spend a couple of hours laying across the engine to replace the 3 rear spark plugs. Not very amused .

Originally Posted by 500hpgtx

What is interesting is that my 3800 sries 2 L67 in my grand prix is absolutely clean. I have been using full synthetic since day 1. When I pulled the intake to put on an intercooler some years back, I was impressed how clean it was.

I presume this engine may be more polluting that the one in your GP. I do not have any experience with US cars other than the PT 3800L, so I can't explain this.

Originally Posted by 500hpgtx

A guy with an L67 supercharged said he was looking for a replacement engine for his 97 GTP. He said he had 355,000 miles on his original engine.

Just guessing: those engines (your GP too) are not placed sideways (with front wheel transaxle). That may be the reason for fouling as the rear is more prone to heath than the front of the engine.
If that guy is looking for another engine he also should be aware of the oil type to use if that engine has already run for tens of k Miles.

[500hpgtx]

The pontiac grand prixs of my style are the 97-03. They are sideways mounted engines. I run Royal Purple full synthetic oil with ROyal purple glass wool oil filter. I will also use lucas synthetic oil stabilizer as well. I now have 107K miles on my grand prix.

I think the 20-50w in the Transport will cushion the worn bearings fairly well. I hope to get quite a few more miles from van...cheers

[Jrs3800]

The 3800 V6 especially 91 and up with the one piece rear main is a very tight engine as far as oil leaks are concerned..

Also the 3800 was one of the lowest friction engines ever produced, all of them were very emissions friendly even without the Cat.. By 94-95 the old L27 was down to the decimal dust as far as emissions was concerned and all of the vans 94-95 easily met the emissions standards...

The 3800 was so clean that it passed emissions without the need of an EGR valve.. after some burnt valves and issues with cracking manifolds due to higher combustion temps GM pur the EGR back on the 3800's from 93 on.. The 88-91 Vin C also had an EGR and were very clean..

Most all modern oil do a good job of cleaning the motor... Synthetic has smaller molecules in a word that can slip by a gasket that Dino may not..

3800's in general are very well sealed and don't tend to leak much at all.. Can't blame a 20 year old valve cover gasket for leaking, same goes for the oil pan..

I have owned nothing but 3800's over the last 20 years, and have run synthetic and dino and switched back and forth.. Never had a single issue with any of them..

My series III in my van burns nothing, doesn't seem to matter if its synthetic or dino nor does the brand seem to matter..

My series II 3800 in my 03 Bonneville burns about a quart in 4000-5000 miles, it always has, currently at 111,000 miles.. It burns oil the same no matter what I use..

My series II in my 95 Bonneville is exactly the same... Burns 3/4 of a quart in 3000 miles, always has... Its always the same no matter what kind of oil I use..

The original 95 L27 in my van say all kinds of oil in its life.. No matter what was used it never burned a drop..

Not being able to go from synthetic, to dino and dino to synthetic is a myth.. I run synthetic in all my lawn and garden equipment as well, never had an issue..

Kev have you thought about running 10-40 until it warms up a bit in your neck of the woods?

[500hpgtx]

Guess JRS3800 and I are cut from the same cloth. We owned a 92 bonneville with a 3800 prior to our Transport and my GTX. Over 22 years now of 3800's
My GTX may burn about a quart every 4k miles I would guess. I never had an oil leak with it since late 99.

I have been running 10w-40 with a quart of lucas oil stabilizer since my wife identified the engine as being loud. (unbelievable hearing).

With my son and daughter now driving this van from time to time, I have been going through a few tie rod ends. The steering wheel is offf to the right by another 40 degrees. I think they just aim straight on the road and hit every pothole that comes along.....:-)

[500hpgtx]

The old "Sawdust in the Trans" trick! Changed oil and filter and installed 2 quarts of lucas oil stabilizer and 3 quarts standard 20w-50 oil.
Amazing how well that combo reduces thae main bearing knock. Oil pressure ver hot is 35 at idle. Pressure cold is at 60psi.....

Makes me want to watch that old 70's moie called "Used Cars" with kurt russel. Very funny movie.......cheers Kev

Forgot to tell you that I bi-passed the EGR in my GTX along with te Cat converter awhile back..