I bought this over the summer and the radiator has since sprung a leak. A couple of questions for those with more experience than me.

Is there anything else that I should look at replacing whether it looks like it needs it or not while I have it out?

I'm debating getting rid of the stock fan and modifying it with an electric fan and shroud. Has anyone done this and is it really worth it? If you have did what did you go with. The only performance improvement that I can see that I might be interested in is better AC performance when idling. The small increase in hp by itself doesn't really do much for me.

Thanks.

Thermostat. Hoses?

Leave the stock fan and shroud., put on a new fan clutch. Add a pusher fan to help A/C if you are running 134a. Wire it to the compressor so that it is only on when the A/C is on.

Thanks.

One more question now that I am shopping for radiators. The one I am taking out has a 1.5 in thick core. Any "Exact Fit" replacement is either 1.25 or 2.25 in thick. Im guessing I need to go with the 1.25 in one but if they both allegedly fit should I go with the larger of the two?

Thanks again.

Yes

Always get the larger.

I'd do thermostat, hoses, and water pump.

Also, the 08+ F150 dual e-fans work well in the OBS. They fit on the radiator perfectly. Just have to fab 2 small brackets for the bottom.

This is on my LS swap. I'm using the factory OBS 34" radiator.

txyaloo said:

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I'd do thermostat, hoses, and water pump.

Also, the 08+ F150 dual e-fans work well in the OBS. They fit on the radiator perfectly. Just have to fab 2 small brackets for the bottom.

This is on my LS swap. I'm using the factory OBS 34" radiator.

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Nice setup (if a bit excessive on the intake clamps ), any details on the brackets you made? Guessing the LS ECM will command the fans on at certain temperatures or when the A/C is on; are there multiple speeds?

The definition of "OBS" keep changing but looks like your truck is a GMT800 ('88-'98 C/K-1500), right? I think the Suburban kept the old squarebody design through 1991, which would include OP's '89.

To the OP: may as well do a proper coolant flush while you're at it. Make sure to drain the block too, both sides (the one on the side with the starter might be a pain to get to). When I did that in my 4.3 I got about another half-gallon of coolant and a little bit of rust out of each side, even after draining the radiator. Then I refilled with 100% RO water (since it's cheaper than distilled and virtually mineral-free), drove enough to circulate that in a hot engine, then drained again (including the block) and refilled with green coolant + distilled water.

Electric fans would help A/C performance (especially on an R-134a conversion), but you'd have to do a standalone control system on your older engine. Hopefully this won't be an issue on the full-size, but on my S10 the R-12 condenser just didn't cut it on 134a -- it was OK when moving, but the A/C was insufficient at idle. When the compressor sprung a leak I replaced the condenser too; swapping the tube-and-fin design for a parallel-flow one made a huge difference. Still with the original engine-driven fan and the A/C is now decent at idle and great when driving.

Quote:

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The definition of "OBS" keep changing but looks like your truck is a GMT800 ('88-'98 C/K-1500)

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'88-98 was GMT400. GMT800 came out in 99 for pickups and 2000 for SUVs. And you're right about the squarebody staying in for the Suburban through 91.

akaggie05 said:

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Quote:

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The definition of "OBS" keep changing but looks like your truck is a GMT800 ('88-'98 C/K-1500)

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'88-98 was GMT400. GMT800 came out in 99 for pickups and 2000 for SUVs. And you're right about the squarebody staying in for the Suburban through 91.

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Oh yeah, of course! Got my numbers mixed up. Both generations were great-looking trucks!

No doubt. My first vehicle was a '94 K5 Blazer. Nostalgia.

Drewmeister said:

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txyaloo said:

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I'd do thermostat, hoses, and water pump.

Also, the 08+ F150 dual e-fans work well in the OBS. They fit on the radiator perfectly. Just have to fab 2 small brackets for the bottom.

This is on my LS swap. I'm using the factory OBS 34" radiator.

---

Nice setup (if a bit excessive on the intake clamps ), any details on the brackets you made? Guessing the LS ECM will command the fans on at certain temperatures or when the A/C is on; are there multiple speeds?

The definition of "OBS" keep changing but looks like your truck is a GMT800 ('88-'98 C/K-1500), right? I think the Suburban kept the old squarebody design through 1991, which would include OP's '89.

To the OP: may as well do a proper coolant flush while you're at it. Make sure to drain the block too, both sides (the one on the side with the starter might be a pain to get to). When I did that in my 4.3 I got about another half-gallon of coolant and a little bit of rust out of each side, even after draining the radiator. Then I refilled with 100% RO water (since it's cheaper than distilled and virtually mineral-free), drove enough to circulate that in a hot engine, then drained again (including the block) and refilled with green coolant + distilled water.

Electric fans would help A/C performance (especially on an R-134a conversion), but you'd have to do a standalone control system on your older engine. Hopefully this won't be an issue on the full-size, but on my S10 the R-12 condenser just didn't cut it on 134a -- it was OK when moving, but the A/C was insufficient at idle. When the compressor sprung a leak I replaced the condenser too; swapping the tube-and-fin design for a parallel-flow one made a huge difference. Still with the original engine-driven fan and the A/C is now decent at idle and great when driving.

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Truck is a GMT400 - 2 door Tahoe. LS ECM does command the fans based on temp, speed, and ac. Brackets were 2 pieces of sheet metal bent as an L. Super simple. I used factory threaded holes in the bottom of the core support, and drilled 2 holes in the bottom of the e-fans for speed nuts.

Unfortunately, the intake clamps were required due to the pipe layout. I'm using an OBS 6.5 diesel airbox. Nothing else really fit in that space well, and I don't like open filter hot air intakes. I also didn't want to go through the hassle of moving the battery to the drivers side. I just reworked my stock Vortec harness so everything is basically OE wiring. All sensors and circuits are on the same fuses and relays as OE. Makes troubleshooting the wiring super simple since you can effectively use a factory OBS wiring diagram.

For GMs, OBS is generally GMT400. NBS is GMT800. NNBS is 08+, etc.