We did a 5.3l swap in a jeep wrangler. Engine runs good, it is out of a 2006 Tahoe and we used the 4l60E from the Tahoe also, computer, throttle controller and Transfer case all came from the same Tahoe. Engine had 6k miles on it when we did the swap.
Used a 3 core aluminum radiator with a fully shrouded fan designed for the Jeep with a Chevy SB conversion. Computer and harness were reworked for stand alone. Installed a 160 thermostat.
Problem is when driving the jeep on the highway over 70mph engine temp climbs slowly (over the course of 15-20 min) up to 250-260 unless you slow down. Around town with the A/C on and 90+ deg outside it runs between 160-180 with no problems. I have checked all the standard stuff, like is the fan running the right direction, good coolant flow, etc... Kinda banging my head agenst the wall at this point. Anyone have any suggestions???

thanks
Dave

 

yeah, that's wierd that it heats up on the highway and not in town.

I'd check the fan rotation.....sounds like at higher speed the airflow from the fan is getting cancelled by the air from the road. In town at lower speed the fan is "pushing" air through the radiator backwards.

good luck.

 

Yea first thing we checked was the fan. Actually tried a fan that flows more air and still no change. I am starting to believe it is not a cooling problem at all. If it was running lean how lean would it need to be to cause a eng temp problem? Kinda pulling at straws now. what kind of HP numbers should we be seeing, just seems like it would have more power than it does. Don't get me wrong it runs good, but it wont spin the 33" tires with 4.10's in the rears. Thinking if mabe a programing issue would cause the temp problem.

 

Do you think the lean cruise is enabled in the computer? Have you checked any of the plugs to rule out the lean issue? Do you have constant fuel pressure at higher speeds?

I know with my '93 S-10 2wd with the 5.3L fuelie, the temp was really high at first but that's because I had air trapped in the system. Once I got the air out, the truck gets to 208* and the fans turn on. The thermostat that I put in was a stock thermostat for a Avalanche, opens at 186*. The truck usually runs about 200 down the highway and its a tight fit in the engine bay. I didn't cut any of the wheel flaps out either.

What temp do you have your fans kicking on at?

 

I don't know anything about "lean cruise" I am guessing it goes into a lean mixture after you are in a cruise state? It seems like it takes lotts of throtle to keep it going 70 and it is right at the kick down. If you come to any slight grade it kicks down to maintain 70.
Fans are programed to come on at 170, and 180 I believe. Right now it only has 1 puller fan on it and that one comes on at 170. I will take a look at the plugs, but I don't suspect I will find anything.
thanks

 

Typically cars overheat at highway speeds when there is a coolant flow issue. More than likely you have a bad water pump, stuck T stat or something of that nature. If while in town it runs cool then obviously your fans are working and the radiator is getting airflow. So you have eliminated the fan as a culprit..... Almost always ends up being the pump when you get high speed overheating.

Good luck.

 

Lean Cruise is not enabled by default. I just got the HPTuners in the mail last week and looking at my stock tune, the lean cruise is set to enable at 256mph (i.e. never). If you have a HPTuners programmer, go to VCM Editor > open your tune > Engine > Fuel Control > Lean Cruise and view the settings.

If you were to drive lets say 50-55mph for 20 minutes, do you have any issues with your temp? Are you radiator hoses warm (i.e. top hose) to make sure the thermostat is indeed opening. Sorry if this is redundant, just trying to double check everything.

In the computer, there is also a setting for Auxiliary Fan 1 disable/enable speed. Might be worth checking into but mine was not enabled by default.

Gremlins can be a PITA especially when you just want to drive the new ride.

 

We have good coolant flow, Pump is working. thermostat opens at 160 just like it should. Fan is coming on at 170 just like it is set to. You can open the cap and watch the coolant flowing.
If I drive at 55-60 it never goes over 205-210 even with the air on.

 

The 5.3 in my Nova has a factory fuel cut off temp of 235, so I don't think the temp should be getting that high or the eng will die. Which temp sending unit are you using for your dash and whats the location of the sender? A sending unit in the head tends to run hottter than a sending unit in the radiator.

 

Going out in left field for a sec, but which style ECM are you using?

 

Drilled and taped the housing behind the thermostat and put the factory sender in for the factory gauge. It's a non issue though because we have checked engine temp with IR temp gauges, 1 aftermarket auto meter gauge and a contact style digital thermometer. All show the temp in the same couple of degrees. Remember we are seeing 260 after a long run at 70 mph (over 15 min of maintained speed)

 

Using the computer that came out of the Tahoe that the engine came from. All the components, Engine, Computer, Wire harness, Transmission, Transfer case, throttle by wire, etc all came from the same Tahoe.

 

Just a couple of things.

Are you using the cylinder head vent lines?

Why do you turn the fans on at 170 degrees?

Is the electric fan pulling or pushing? Pulling is best. If they are running going down the road the may impede air flow at high speed.

I have two LS swaps. First is a 4.8 in a 98 wrangler. 2000 4.8 with mechanical fan and 4.0 radiator. Stock thermostat. Runs at 195 degrees no matter the temp out side.

Second is a 99 Wrangler with a 2000 LS1. Novak radiator with Spal fan. Temp sensor in the lower left corner of the radiator. Painless sensor that is on at 205 degrees and off at 195 degrees.

It runs very cool no matter what the driving speeds.

Is there a a small chance of a bad head gasket or cracked head? Worth doing a pressure test? Either can put allot of heat in the cooling system.

When you get to 260 degrees does it vent out of the radiator?

Jim

 

The PCM should still shut the fuel off @ 235, unless someone has set the fuel shut off temp higher. If the steam line in the front of the heads isn't hooked up you'd probably have a hot spot in the heads, but 260. Can you run the jeep while scanning it, will show what PCM is reading. Rad is the best place to get temp from. Sorry couldn't help more, I wanna see how this one plays out.

 

how did you burp the system?? let it cool and remove the radiator cap and see if it burps, if so you may need to do this several times, other then that not sure, good luck.

 

I'm not sure who told you that, but not true at all.

 

i have done several swaps and have always had the best luck filling the coolant through the upper rad hose right into the top of the water pump,, other wise you get major air in the system,, just pull the upper hose off the radiator , tip it up and full it with coolant,, this will fill the block completely then put the hose back on the radiator and make sure the rad is topped off also

 

It could be very possible your fans are impeiden your air flow at high speeds.I had that same problem and removed my e-fan and put the mechanical fan and clutch back on and that fixed my problem.Could be wrong though.
Mike

 

I still think it may be the pump. Every car I have seen with highway related overheating ends up the pump and they ALL have flowed down low while idling and visibly appear fine.

 

Check your heater core or shutoff valve. THE LS ENGINE NEEDS COOLANT FLOW ALL THE TIME THRU THE HEATER CORE. Sorry for the yelling. Make sure you have constant flow. If the heat is off then you need to install a heater valve out of a Ranger or GTO. One that still allows coolant to flow thru the heater hoses. If you doubt your setup then just run a U-shaped heater hose at the water pump temporarily and see if it still overheats.

The first thing you notice about LS engines are that they don't hold much coolant compared to the old small block.


You can still run 15/1 A/F ratio at light cruise and it should not overheat.

The newer 5.3s are great. They run good all the time and are over 300 hp.