hubcap706

I have a recently built LQ4 that has developed several small coolant leaks. The motor and trans are mounted in the truck, but the truck hasn’t left my shop due to needing a few more things to get it on the road. The motor has only been fired up about 5 times, 3 short idles, 1 of those was when coolant was added to the system, and the other was last weekend and it only idled for a couple of minutes.

I know that one of the leaks is the coolant crossover line in the front and another is the water pump gasket, both of which I intend to fix on my next free weekend.
The mysterious leak that is puddling in a different spot is the one (or more) that I cannot locate. it seems to be a minor leak that is dripping on the passenger and driver side near the back of the engine. The rear steam ports are blocked off and have already been checked. The leaks have only recently started with the sudden temperature drops going into winter here in TN. Lastly, the leaks have all happened when the truck is not running.

Do any of you have any suggestions of “leak points” near the back of the engine?

I plan on pressurizing the system to find the leak as well, but wanted to ask if anyone knew of a good place to check before then.

thanks!!

grinder11

iTrader: (1)

If the leaks happen when it's not running, are we assuming it was running, got up to normal temp, and was then shut off? Any engine heat sinks after it stops running/moving. Heat sink means coolant temps rise another 5°-10°. That means even more pressure. If you're still running the factory spring type hose clamps, they can lose tension sometimes as they get 15-20 years old. Mine did. I was ready to pull the heads and install new head gaskets. Mine never had coolant under the car. But it was going somewhere. It was leaking slowly by one heater hose at the T-stat. It would evaporate. I installed new, traditional worm type band clamps, and no more issues. FWIW......

hubcap706

Thanks for sharing! Any info is helpful at this point. The more post that I read on rear side coolant leaks, the more I start wondering if it’s a head gasket.

The leak didn’t show up until a couple of days after the motor ran. And seems to continue to leak as it sits. Which seems to be odd. It does seem to happen and started happening when the outside temperature dropped below 50 deg.

Everything is pretty much new on the motor. They’re 317 heads and new head gaskets. I have A coolant temp sensor in each head as well, and neither are leaking. Also, the heater hose is a bypass hose as I am not running heat or AC.

The passenger side is leaking down and then dripping onto the starter, and then to the ground. The driver side seems to be running down near the block and transmission bell housing interface

hubcap706

To add more information.

The heads were milled 0.010 and the block was cleaned by the shop that did the rotating assembly.

I used ARP head bolts and BTR LS9 multilayered head gaskets.

jasons69chevelle

Have you looked at the cylinder head freeze plugs?

Rick Dorion

iTrader: (1)

When I put a set of heads on my LM7 I experienced the same thing. In my case the little gaskets under the steam ports weren't correctly installed. In fact, they were so compressed I didn't see them the first time.

hubcap706

Jason, I did check both plugs in the heads and they were bone dry.

Rick, I’m going to check the rear ports first thing this weekend. On the front steam ports, some of the the coolant is pooling up around the head bolt from what I think is due to the engine being at an angle and some runs downs the front of the block.
After looking at a picture of the rear steam port block off kit, it appears that the coolant would not pool up, but rather run down between the block and bell housing near the same location as the leak that I am experiencing.
The coolant on my drip pan is nearly identical for each side in terms of the amount of coolant and the puddle location. It’s definitely going to be my first visit, and I’m almost positive that I will have the same experience that you mentioned

Old Buzzard

A rad pressure tester and some dye is a way to track it.....

hubcap706

Most definitely Old Buzzard. I’ll be sure to report back following the pressure test.

Thanks for the input everyone!

grinder11

iTrader: (1)

Maybe try loosening the expansion tank cap, and see if it still leaks. What brand head gaskets were used? I always stick with GM gaskets, but I have an LS7. They work well for my application. Again, if youre running the OEM tension clamps, look closely where they enter and exit the firewall. Maybe try a traditional worm type band clamp.....

LilJayV10

iTrader: (39)

More than likely its running down the front of the engine, oil pan rail and dripping off there.

Fix the known leaks first then try and figure out the mystery one.

FU_I_AM_UltraZ

iTrader: (20)

Hell, you can have a blown head gasket that the tear is not leaking into the cylinder, but on outer edge, the side of the block. I've come across a couple early year LM7 trucks with 100k to under 200k miles running green coolant (coincidental maybe vs dexcool?). But heads had such horrible corrosion/pitting that it was leaking down the side of the block, had to replace the heads for the customer. The 1 truck was an 01 Silverado 5.3 stepside that ran great minus coolant leak. Laid down rubber in parking lot before pulling into my shop.

hubcap706

UPDATE: This was spot on. I ran new crossover lines and fittings. I let the engine idle for about 2 minutes and cut the truck off. No leak then, and a week of sitting and still no leaks. Seems as if the known leak on each of the front coolant crossover passages was the only leak, running down the front of the motor as well as the back of the motor.

Thanks again for all of the advice!

B52bombardier1

Thanks for coming back to tell us what happened and that should happen a lot more often.

Really appreciate it.

Rick