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Overfilling transmission fluid
11-21-2012, 04:50 AM
Post: #1
Overfilling transmission fluid
Use Goodbye Spammer on jaypeazy.
I just dropped $1100 at a reputable shop to fix multiple leaks on my recently purchased 01' Silverado 1500 ext cab. They replaced the rear main seal, the oil pan gasket and the transmition pan gasket. Several days later it occurred to me that I should check both dipsticks as I was still seeing puddles under my truck (now the puddles seemed a lot bigger.)

I checked the oil and tranny dipsticks and they were both showing a lot higher than the "Fill" line, especially the transmission fluid. Oil dipstick is about a half inch above the line. The trans fluid was over an inch and a half above the fill line. When I got to work I made sure to park in a spot that I've never parked before and a space that had older and smaller stains. When I left work I moved my truck and I saw a puddle (not just a stain) that is about the size of 2 of my boot soles or larger (I wear size 15 boots.) I did this at my apartment and at work for the next few days with the same results. I took it back to the shop the next monday, as the shop is closed on weekends, and they told me that there must have been so much fluid all over the bottom of my truck on the first visit that they probably just missed the transmission pump & tranny seal leak. They also stated that overfilling the tansmission fluid wasn't a big deal and would not have caused the transmission pump to fail and puddles that size aren't much more than a couple of capfulls of fluid. I've read forums that agree with that and I've read plenty of them that don't.

On top of all of that, my transmission is starting to hesitate between gears (automatic) escpecially when I put it in reverse. It's not slipping hard where you can feel it drop and shake the whole truck but it wasn't doing this before I brought my truck in for the inital leak. They told me that probably means I'll need to replace the transmission in the near future. My questions are:

1. Could overfilling the transmission fluid (esp. that heavy) have blown out my transmission pump?

2. If not, why do you think the puddles got so much bigger (originally 4" - 5") after they replaced the trans pan seal? Is it just a simple release of all that excess fluid?

3. Do you think 2 caps full of trans fluid could cause a puddle as big as the soles of 2 size 15 combat boots? (maybe 2 baseball caps full?)

4. Do you think the hesitating transmission will need replacemet soon or could that just be the temporary result of foamy fluid (because of the overfill)?

5. If it will need replacement, could their shoddy work have caused this?

6. And how long could I drive this truck before I would need to rebuild the tranny? (I'm thinking of taking it to a transmission shop I trust about 150 miles away in Houston and want to know if it can make the drive)


I appreciate your help guys. If you don't know any of the answers please let me know where you think I might find them. Thanks again!

~ "The reward of a job well done is to have done it"
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11-21-2012, 10:00 AM
Post: #2
RE: Overfilling transmission fluid
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How many miles on the tranny? Can you tell were the leak is coming from? Is it the tailshaft,pan, filler tube? As for the shipping a lot of times if the tranny was going and you change all the nasty fluid out it could make it slip more. ( All the old chunks help sometimes:rolleyesSmile
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11-21-2012, 12:58 PM
Post: #3
RE: Overfilling transmission fluid
As 4x4HD stated, the new fluid can cause more issues if the tranny was not serviced properly. That said, I have seen tranmission seals go because a tranny was overfilled.

2003 Silverado Z71
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11-21-2012, 02:33 PM
Post: #4
RE: Overfilling transmission fluid
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(11-21-2012 10:00 AM)4X4HD Wrote:  How many miles on the tranny? Can you tell were the leak is coming from? Is it the tailshaft,pan, filler tube? As for the slipping a lot of times if the tranny was going and you change all the nasty fluid out it could make it slip more. ( All the old chunks help sometimes:rolleyesSmile


About 175k miles on the tranny. The shop took me under the truck while it was on the lift and tried to show me where the leak was coming from. They were shining the light inside the head of the transmission (right where it meets the engine) but it was hard to see. They also showed me a leak right at the tranny seal by the engine.

I bought if from a used car dealer who sold it a grand or two under market value. I had assumed because of that there would be some repairs to make on it. It had been his daily driver for the last 66k miles and he said that he needed to sell it so he could buy 2 smaller cars to sell quickly and start saving up for his taxes that were coming up soon. My Dad has been involved with a used car lot owned by a friend of his for several years now and was with me when I checked it out. He felt that the guy was pretty legit. That being said I doubt the guy was going to perform any major surgery on a vehicle he was originally planning to sell. Although he did seem to get a little misty-eyed letting her go (the silverado).

I had a "Auto-P.I." come do an inspection on it before I bought it and he said it was a good buy as well for whatever that is worth.

Part of the Insp. results:

Belts: SATISFACTORY
Engine Leaks: REPAIRS

There seem to only be 2 belts. One looks just about new. The a/c belt (which is hard to see) looks like shit and is littered with cracks Dodgy

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Tdlimited, I appreciate the info. That's what I was afraid of.
I've seen arguments on both sides but the side you guys mention makes more sense. Looks like I might be having to take a trip to Houston to the tranny specialist. There another reputable auto-shop out here that also does tranny work but I'm afraid they might sub it out and I'd really like to take it to the guy who will actually be working on it...

~ "The reward of a job well done is to have done it"
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11-22-2012, 09:26 PM
Post: #5
RE: Overfilling transmission fluid
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Today my transmission started slipping on the way to work. I've read more forums and I've been seeing a lot of feedback saying that if you overfill a transmission (with trans fluid) that it can blow out the trans. pump and the transmission's main seal which are exactly the 2 issues the shop said now needed to be fixed. One of the sites stated that just a half quart too much can cause this. The puddles I've been seeing are about 14-18" long and about 8" wide. I get these twice daily. One at work and one at my apartment and I'm not parking in the same spot twice nor am I parking in places with large pre-existing stains. I refuse to believe that 2 cap-fulls of trans fluid will cause stains that big...BALLS!!!

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11-23-2012, 12:33 PM
Post: #6
RE: Overfilling transmission fluid
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The tranny must be low on fluid now. It could be slipping now because it is low. It needs to be fixed but if you keep the fluid up it will help not damage anything more.
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11-23-2012, 05:09 PM
Post: #7
RE: Overfilling transmission fluid
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Actually the fluid is still showing a little high on the stick but I've been granny driving since yesterday and haven't felt another slip. I've read in other forums that when the trans fluid is overfilled it starts to foam up. Then that foam gets sent through the lines instead of actual liquid and that means the parts aren't getting lubed properly which also means they can start grinding and filling your tranny full of metal shavings...

~ "The reward of a job well done is to have done it"
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11-24-2012, 03:07 AM
Post: #8
RE: Overfilling transmission fluid
One opinion to consider so you can get the truck to Houston is to drain the tranny again and remove all of the metal from pan and filter. Install new filter and pan gasket and fill to proper level. i had a 1982 blazer that lost the tranny at the Maine / Newhamshire line. Buddies of mine did this in the autoparts store parking lot and I was able to go another 100 miles into maine and back home to CT before the tranny really went to crap. Don't know if that is cheaper then towing to the shop you want or not.

2003 Silverado Z71
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11-24-2012, 04:05 PM
Post: #9
RE: Overfilling transmission fluid
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(11-24-2012 03:07 AM)Tdlimited Wrote:  One opinion to consider so you can get the truck to Houston is to drain the tranny again and remove all of the metal from pan and filter. Install new filter and pan gasket and fill to proper level. i had a 1982 blazer that lost the tranny at the Maine / Newhamshire line. Buddies of mine did this in the autoparts store parking lot and I was able to go another 100 miles into maine and back home to CT before the tranny really went to crap. Don't know if that is cheaper then towing to the shop you want or not.




Great idea!! I would have never thought of that but it makes perfect sense. Thanks, brother.

Luckily I've found a local transmission shop with a good reputation that I'm going to take a shot at. Thanksgiving was yesterday and most of the shops in this town are closed on the weekends so I'll have to wait til Monday morning to bring it in. Would be nice if I hadn't wrecked my bike in September. A second vehicle would be helpful. Smile

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11-27-2012, 07:30 PM
Post: #10
RE: Overfilling transmission fluid
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I took the truck to a reputable transmission shop today (yelp.com, angieslist & BBB) and he told me that, while overfilling the fluid could cause the trans pump and main seal to blow out, that would most likely only happen if the transmission was due for repair anyway.

He also said that since the 40's, tranny's have been built with vents that will dump excess fluid (even though that's a fire hazzard) so it's unlikely that overfilling can blow the pump/seal of a good transmission. He hasn't opened it up yet so he can't yet determine whether the last shop caused it until he takes a look inside tomorrow. Maybe the pump and seal were destroyed from the fire caused by the vent dumps??? Maybe I'm reaching? Angel


So far it seems:

Good Transmission - overfilling will most likely just cause the vents to dump the excess oil onto your hot metal surfaces to possibly cause a fire.

Worn transmission - overfilling might cause the pump and main tranny seal to blow out making it necessary to replace/rebuild transmission earlier than needed.


The main question now is "how many more miles could I have gotten out of that tranny if they hadn't overfilled it?" I mean seriously, how can a mechanic not know how to properly fill fluids? Ignorant, hateful or just plain sloppy? Either way the guy could use some serious brain adjusting.

~ "The reward of a job well done is to have done it"
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11-28-2012, 02:58 AM
Post: #11
RE: Overfilling transmission fluid
I know what you mean. When that Blazer of mine did get repaired, I had the 700 removed and put a 400 in so I would not have the problem again. Two years later, transmission goes again. The so called great transmission shop put a rebuilt 400 in the truck with the wrong torque converter. Complete rebuild again. It stinks that you won't know the answer to that and there's not much you can do about it.

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01-03-2013, 09:54 AM (This post was last modified: 01-03-2013 09:55 AM by White1500.)
Post: #12
RE: Overfilling transmission fluid
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Last year I decided to change the fluid in around September/October, and a month or so later it decides to slip and call it a day (torque converter or something like that).

So, the moral of the story is that if it's an old tranny, leave the fluid or prepare to get a new (rebuilt) one.

You're lucky that it has still been working well, but when you least expect it it's going to leave you stranded. My advice is to take care of the issue asap.

And I'd also recommend installing new engine and tranny mounts while you or the mechanics are under there.

Good luck!

'00 Silverado; Ext. Cab, 5.3L
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