5.7 from 99 GMC Yukon having heat issues

[brycebba]

Ok so hear is my flood of information. I transplanted a 99 GMC Yukon 5.7 of mine into my 97 Jeep Wrangler TJ. I had the engine rebuilt while it was out but no performance changes made. Here is the current configuration.

• AC condenser is in front of radiator
• Then a 4 core radiator with left side "bottle" being the transmission fluid cooler
• Flexalite 2500 cfm loboy fan
• A 170 degree thermostat
• Computer is programmed to kick fan on at 185 degrees. no hot tuning or anything

Now, I live in Vegas where it is about 100 during the day right now. Let me tell you two scenarios.

Scenario 1: The Freeway. I can go about 25 miles before the temperature of the transmission and the coolant start going over 210 degrees on my auto meter gauges. These 25 miles usually consist of 65mph speeds and about 2250 rpms. Temps will continue to increase if I keep going.

Scenario 2: Around Town. I can drive surface streets around town at various speeds all at 45mph or below for about 40 minutes before getting into the same boat 210 degrees on engine coolant and transmission and it will continue to climb if I keep going.

What could I be looking at here? I know this isn't a jeep forum but I figure this drivetrain is the right fit for here. I see plenty of gmt 400s cruising around and they aren't overheating so I have to figure out what I can do.

Thanks guys!

Bryce

 

[evilunclegrimace]

Do you have a fan shroud on the radiator? Is the water pump the correct rotation? Is the water pump impeller slipping or damaged?

 

[tachrev]

If it is overheating at highway speeds, then its not the fan.

Assuming the water pump doesn't have a mechanical issue and there are no air pockets in the system, it is flat out not enough air flow through the cooling stack, or not enough cooling surface area.

Do most v8 swap guys use that 4 core radiator? I would think someone has found something that works.

 

[brycebba]

Do you have a fan shroud on the radiator? Is the water pump the correct rotation? Is the water pump impeller slipping or damaged?

I do not have a shroud, I don't have the room for one. As for the water pump, it only has about 25k miles but I suppose it may be an issue. What would I be looking for?

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[brycebba]

If it is overheating at highway speeds, then its not the fan.

Assuming the water pump doesn't have a mechanical issue and there are no air pockets in the system, it is flat out not enough air flow through the cooling stack, or not enough cooling surface area.

Do most v8 swap guys use that 4 core radiator? I would think someone has found something that works.

The radiator was built by a company that specializes in these conversions so I think it's ok. I don't currently have the ac system charged so would a helpful test be to pull the condenser? Also looking for ideas on testing the water pump.

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[PlayingWithTBI]

Is your water temp sender the one on the head between cylinders 1 & 3? In my gen 1 5.7 I've found that sensor reads higher than the one feeding the ECM. While it reads 210 my ECM is seeing 194 (with a 194 T-stat) when I sit a a light my gauge goes as high as 216 while the ECM sees 196. I have aluminum heads but IMO these engines just don't have enough flow through the heads as apposed to the block/intake. Do you have a way to scan and see what's going on in your PCM?

I had the same issue as you're describing with mine before I rebuilt it - blown head gaskets between #s 5&7 and 6&8.

 

[brycebba]

Is your water temp sender the one on the head between cylinders 1 & 3? In my gen 1 5.7 I've found that sensor reads higher than the one feeding the ECM. While it reads 210 my ECM is seeing 194 (with a 194 T-stat) when I sit a a light my gauge goes as high as 216 while the ECM sees 196. I have aluminum heads but IMO these engines just don't have enough flow through the heads as apposed to the block/intake. Do you have a way to scan and see what's going on in your PCM?

I had the same issue as you're describing with mine before I rebuilt it - blown head gaskets between #s 5&7 and 6&8.

Yes I believe that's where the sending
is for my coolant temp.i do have a way to check the computer so I will do that next time I get it up to that 210 mark and report back. It runs excellent so I doubt anything is wrong with the engine. It never ran this good in my Yukon lol...