Coolant leak at bellhousing after brand new GM Crate Motor install - SOLVED

[hank89]

So I just put in a new gm crate motor this weekend in my 99 tahoe. I was so excited when I got everything back together, being this was the first time I pulled a motor and put a new one in. And it started right up!

And then I noticed a day later that it was losing coolant and there was a drip from the transmission bell housing.

I cannot tell you how disappointing this is after spending about 8k between the new crate motor and all the new parts I added. I put in the felpro gaskets with new bolts w/ threadlocker...and I used the black rtv in the felpro kit for the chinawalls.

Since having the tahoe, I had a shop put in gaskets at 100k miles; then I replaced them again with felpros at 175k miles...and then I replaced the engine at 253k miles. I cannot tell you how many hundreds of dollars I spent on antifreeze for the first motor.

Now my new engine is already leaking coolant. The lower intake on the 5.7 is a P.O.S. I cannot believe someone has not made an intake that actually works and doesn't leak.

I am beyond pissed off.

So for those of you thinking about replacing your 5.7 with another.... If I had to do it again, i would of spent a few more dollars and got a brand new GM engine with completely new fuel injection system. Maybe an LS or one of the ramjets.

 

[wjburken]

Have you checked your heater hoses near the firewall?

I agree, the lower intake design on that gen one motor is a PITA. I had to replace one on my sons ‘97 K1500 last January when it was 10° outside.

 

[east302]

Adding to the above, the knock sensor could (in theory) leak bad enough for air to blow coolant back that far. I did have a bad hose at the intake quick connect that did a slow leak that drifted down the intake/valve cover valley back toward the starter.

But, yeah, that sucks. The reinforced Felpro gaskets tend to last longer than their cheaper non-reinforced ones, but both should make it a hell of a lot longer than a day.

Did you put RTV on both the top and bottom of the little gasket tab where it meets the china wall? The RTV was allowed to cure? Usually, by the time I’ve gotten everything back together it’s had plenty of time to set.

 

[WHYTNOYZ]

I have them on both front and rear drilled/slotted and it's been about a year and some change without anybissues I can think of. Actually I bought them blacked out and during the break in process they turned to the standard metallic color which was a bit of a number since my rides all blacked out. Pads are decent as well.

 

[OR VietVet]

Coolant drip on the outside and dripping off the bell housing or coolant dripping from inside the bell housing? Could be any of the above or a welch/freeze plug at back of block if from inside the bell housing.

 

[hank89]

Have you checked your heater hoses near the firewall?

I agree, the lower intake design on that gen one motor is a PITA. I had to replace one on my sons ‘97 K1500 last January when it was 10° outside.

I don't believe I have heater hoses near the firewall. I replaced the 2 heater hoses (3/4" w/ plastic quick connect into the lower intake and the 5/8" at the water pump). I have a tahoe which doesn't have the rear heater like the suburban.

 

[hank89]

Adding to the above, the knock sensor could (in theory) leak bad enough for air to blow coolant back that far. I did have a bad hose at the intake quick connect that did a slow leak that drifted down the intake/valve cover valley back toward the starter.

But, yeah, that sucks. The reinforced Felpro gaskets tend to last longer than their cheaper non-reinforced ones, but both should make it a hell of a lot longer than a day.

Did you put RTV on both the top and bottom of the little gasket tab where it meets the china wall? The RTV was allowed to cure? Usually, by the time I’ve gotten everything back together it’s had plenty of time to set.

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View attachment 386830

Thanks east302...I will check the knock sensor...I put a new one on. Yes...I did put RTV on the top and bottom of the gasket tab/return at the china wall.

I used the rtv that came with the MIK98000T kit. There wasn't much in the kit...and I did the front wall first, then when i did the back, i'm wondering if i didn't put enough on. I did give it time to set where it wasn't sticking.

I'm going to get a camera and see if I can locate exactly where it is coming from.

Thank you for all the info!!!

 

[hank89]

Coolant drip on the outside and dripping off the bell housing or coolant dripping from inside the bell housing? Could be any of the above or a welch/freeze plug at back of block if from inside the bell housing.

Thanks for the reply. Will look into this further. I hope it is not the freeze plug(s). this is a brand-new gm crate motor.

 

[east302]

Thanks east302...I will check the knock sensor...I put a new one on. Yes...I did put RTV on the top and bottom of the gasket tab/return at the china wall.

I used the rtv that came with the MIK98000T kit. There wasn't much in the kit...and I did the front wall first, then when i did the back, i'm wondering if i didn't put enough on. I did give it time to set where it wasn't sticking.

I'm going to get a camera and see if I can locate exactly where it is coming from.

Thank you for all the info!!!

If that RTV at the wall was somehow “not right” enough to send coolant down the back of the block, then I’d think that you would see coolant in the oil fairly quickly. It wouldn’t hurt to drain it and see, but an external leak at a hose or something just sounds more likely.

A coolant pressure test may be in order.

Regarding the heater hoses, that poster was referring to the two lines going through the firewall under the a/c accumulator.

 

[exp500]

One of my work trucks had a small unable to locate coolant leak. Took about 60 days of watching until either the leak got bigger or sunight was perfect- was leaking at plastic tees for rear heat and squirting a tiny stream towards exhaust manifold/spark plug. Leak was about 1 quart a week. A quick wrap in paper towel verified exact location.

 

[OR VietVet]

I don't believe I have heater hoses near the firewall. I replaced the 2 heater hoses (3/4" w/ plastic quick connect into the lower intake and the 5/8" at the water pump). I have a tahoe which doesn't have the rear heater like the suburban.

 

[YukonGTmaster]

Check the quick disconnect fitting for the heater line at the intake manifold, passenger side. I had one that wasn't seating anymore, and coolant was running all the way back along the rocker cover, down the back of the motor. Took me a long time to diagnose. Get the GM part, not the Dorman if possible.

 

[hank89]

View attachment 386896

View attachment 386897

My apologies. I thought someone was referring to heater hoses coming out of the back of the engine at the firewall.

Yes. I did replace the 3/4" and 5/8" heater hose lines that connect to the heater core at the firewall with new Gates Green stripe hoses. I also put on a new gm genuine heater valve (T). Unfortunately I put on a dorman quick connect...but I don't see any leaks there. All the heater stuff is new...except the heater core (original)...I pulled the carpet back thinking maybe I have a pin hole leak in the heater core...carpet is dry.

Will pressure test it when I get a chance this weekend. Thanks for all the help everyone !!!!

 

[neil_f_real]

+1 to what OR VietVet said. Since your block is new, perhaps one of the core plugs is not sealing properly?

I experienced a leak in the same location about 3 months after replacing my intake gaskets with FelPro gaskets. Thought perhaps I did a poor repair. It turned out that one of the two rear core (freeze) plugs was corroded and leaking. It was a transmission-out job to replace both core plugs.

 

[Summajet]

I would suggest renting the water coolant pressure testing kit from Oriellys, AutoZone, and advance. It would make it easier to see where the leak is coming from and not burn yourself on the hot exhaust or manifold. Pump it up to no greater than 15 lb psi.
It should help spot the leak quicker.

 

[HACK BLOCK]

just add dye to it

 

[hank89]

Just wanted to thank everyone that replied to this thread! The coolant leak was my dumbass fault! I just didn't connect the hose at the top of the waterpump! The new GM Crate Engine has been flawless and is great! I waited to post on it, just to be sure it wasn't leaking!!!

Thanks again everyone!

 

[willxfs]

Good to hear you are all squared away and thanks for following up.