lxcoupe

iTrader: (8)

Hey guys, I recently did an L86 swap into a C10 pickup using a BTR DOD delete kit and the LT4 head gaskets part # 12654622 that they provided in May 2022 with the DoD delete kit. Started the motor and it purrs, runs smooth, but I can't get the tstat to open and truck overheats. Replaced tstat same issue. Filled truck through water pump inlet and ran truck with the front jacked up. Same issue. Lower radiator hose stays cold the whole time. I bypassed heater core with loop hose, same thing. Fans turn on normally at 215-220 but coolant gets to 230-240 and the water in the radiator is cold. The LT4 headgaskets are clearly marked "front" and I have assembled dozens of LS/LT motors but lately I heard there were some that were marked front incorrectly. I didn't verify that the coolant holes were lined up but I can see the tabs on the head gaskets visible near the headers and they're oriented correctly. If I disconnect steam vent hose, nothing comes out. Any other ideas before I yank the heads off for no reason?

Che70velle

iTrader: (6)

Don’t pull the heads. Remove the water pump (pita..yes) and stick your finger in the center round hole, upside down, and bend it upwards. If you feel the headgasket, you put ‘em on backwards. If you feel nothing, your good there, and need to look elsewhere here. If the gaskets are on right, put it back together without a stat, and when you start it, watch for coolant flow in the radiator with the cap off. Should be moving a lot of coolant. If it is, your pump is ok. If it’s not, could be a pump or a clogged radiator. I’ve seen a lot of clogged radiators from DexCool. Put the stat back in and start it back up…let it get up to temp. Feel for cool spots on the radiator core, or use a laser temp gun. If you’ve got cool spots, radiator is clogged and can be cleaned out or get a new one. This is the steps I’d take personally. Lot of work, but way easier than pulling heads to look at gaskets.

lxcoupe

iTrader: (8)

Excellent advice. I will do all of that tonight and update the thread.

lxcoupe

iTrader: (8)

So I got the water pump off and stuck my finger through the top holes and I did not hit gasket on either side. I had to stick my finger way up there, but I finally felt the rough casting which is what I believe is the coolant passages in the cylinder heads. So I think it’s safe to say can eliminate the gaskets being reversed. That being said, I was thinking that it almost has to be the water pump because how could the water pump be working properly if the lower radiator hose stays cold permanently? Also, there is no water coming out of the steam hose on the top of the water pump when the motor is running. It just seems to me that it can’t be a radiator problem or if it is a radiator problem it’s primarily a water pump problem. It’s just strange because I have a spare pump here and spinning it by hand, comparing it to the old pump everything seems identical. I also blew out all the passages in the block and pump to see if maybe there was some paper or some thing from when I was cleaning the deck of the block for the new headgaskets, but nothing came out. I guess I’ll throw everything back together with the new pump and hope for the best.

Che70velle

iTrader: (6)

Yessir, you can feel inside the actual head casting with your finger tip…so your gaskets are correct. Throw the other pump at it and keep us posted.

Tommy42088

I actually went through the same thing about a month ago and I pulled my heads to find out that my gaskets were actually installed correctly. It took me at least an hour to get mine to bleed all the air our and finally stop overheating. I jacked the front up and poured water into the water pump side and that didn't work and then I tried the radiator side and that didn't work but at the same time I still got alot of air out of it that way but it still started overheating as I completed this. I turned it off and let it cool overnight and the next day I filled the radiator up and disconnected the steam lines and kept pouring fluid in it and the last bit of air came out the steam lines and it didn't run hot anymore. I then took it on a 70 mile trip and didn't run hot, mind you this was 85 degree weather. Oh and I also changes my waterpump and thermostat in the process and neither of those optioned changed anything. Long story short man be patient and get the air out the system.

avchz

haha, I've installed a LT 5.3 head gasket backwards before... At first the vehicle will run fine, but afterwards it will start making a grinding sound. Easiest way to tell if the gasket is installed correctly if the heads already on. Run your fingers on the bottom of the head where it meets the block under the exhaust there should be a tab sticking out. that tab is a part of the gasket. if its towards the front of the engine your good, if its more towards the rear of the engine, it might be installed incorrectly. There's a actually a bulletin on this on service information.

Mickyinks

I bleed mine by filling the radiator with coolant, stick radiator cap back on, disconnecting the steam vent hose at the steam pipe end, the hose runs to radiator, stick a funnel in the end ,lift it high and pour coolant in... May seem a bit backward but in effect it makes the height im holding up the steam vent hose the highest in the system . As you pour in coolant itll push all the air out thru steam vent pipe. Never fails this way.
The other way which works well is get a big bottle of coke , cut bottom out of it, make a rubber gasket on spout and stick tht in your radiator, once system is full the coolant will fill coke bottle making it the highest lvl in the system , start the car and all air will purge out thru coke bottle
Same concept as jacking front of your car up, making the radiator cap the highest point in the system for air to bleed thru

Che70velle

iTrader: (6)

What Mick is talking about (the Coke bottle method) is something like this from Summit…https://www.summitracing.com/parts/oes-87009

Mickyinks

For $20 thats a much better option. Im gunna track one down today, someone must sell em in oz