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350 xj Cooling -- help

J

jmg222

NAXJA Forum User
NAXJA Member
Location
US
having a cooling issue that's driving me batty. I'm running a circa 1988 chevy 350, mild cam, efi, stock heads, novak aluminum rad w/ 3 spal e fans in my 88 XJ. Everything was working fine earlier this year -- rock crawling at rausche creek, zero overheating, driving at normal speeds on the highway, no issue. I grenade my d35 over the summer, replaced that with a f8.8, and since then, have had nothing but headaches with overheating. I'm sure one has nothing to do with the other --- only mention it because it was sitting around for a few weeks in a shop, not being driven. The day I get it back, it overheats on the drive home. This is driving me crazy. At idle, it sheds heat with no problem. But if I go over 2200 rpm or so, regardless of how fast I'm going, heat starts slowly climbing. At rausche creek two weeks ago, no issues with low idle crawling, but heading back on a long uphill access road, hit 230 before I had to pull over.
I'm at the point where I think I may have a blown head gasket (I'm going to do a compression test when I get back this week), but anything else on the "idiot" checklist I missed? This is what I've done:
  • confirmed tstat was working properly and in the right orientation. tried a 160 degree tstat, no difference. Tried running with no tstat, no difference
  • lower rad hose looked snarky, thought maybe it was collapsing. replaced, no difference.
  • checked timing -- running 12 degrees initial timing, 34 degrees total timing (timing was retarded --26 degrees total timing). no difference
  • Replaced water pump. Tried a stock replacement from advanced auto and a high-flow from edlebrock. Confirmed both were reverse rotation pumps. No difference.
  • Raised a/f ratio at cruise to 13.8. No difference.
  • changed icm (I know, but I figured what the hell)
  • confirmed all fans are working. Set them to turn on at 180.
  • changed tensioner and serpentine belt (it was late and I ran out of ideas)
  • pulled winch, lights, and everything else from the front of the truck. Thought this may be impeding air flow. No difference
 
any deep thoughts on this? this is driving me batty.
I've tested the coolant with a hydrocarbon kit -- everything came up negative, so no oil in the antifreeze.
Also did a compression test on each cylinder, all cylinders are within spec. So, I think I can rule out a blown head gasket.
 
You try back flushing the system and see if something is clogged?

Grab a laser thermostat. When it gets warm, see if temps are consistant across both heads, front to back, and the radiator.

Is the radiator cooler at the outlet than the inlet? And by how much?
 
cal said:
You try back flushing the system and see if something is clogged?

Grab a laser thermostat. When it gets warm, see if temps are consistant across both heads, front to back, and the radiator.

Is the radiator cooler at the outlet than the inlet? And by how much?
Click to expand...

yeah, I knew I forgot a few things:

* Flushed twice. Is "back flushing" any different than a normal flush? Burped the system.
* I laser-checked the exhaust manifolds on both sides, each exhaust was between 400-450 degrees when the truck was at 200 degrees.
* there is a difference in temp between inlet and outlet on the rad, though not by much. with the truck at 180 degrees, the inlet is at 162, the outlet is at 153. I have been on the phone with Novak trying to figure out if the rad needs to be replaced, they say 9 degrees differential at that temp is well within normal operation.
 
Sadly I don't have a number on how much it should cool, but 9 degrees just does not sound like enough to me.
 
I leave my rad fan on in Summer. It'll range from 180 which is what the stat is to 215. I changed pullies to a 1:1 setup. The temp was scary before and the pump was overdriven. Been ironing out little bugs here and there but it's been my daily for four rears now.
 
When you say over heats, is it actually boiling over or is it just the gauge reading high?

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cabjeepster said:
When you say over heats, is it actually boiling over or is it just the gauge reading high?

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Click to expand...

at idle and stop-and-go traffic, it sheds heat with no problem, so I don't think airflow is an issue. At anything over off-idle, say 1500 rpm or so, regardless of how fast or slow I'm going (2000RPM in 4lo in first gear results in same level of overheating as 2000 RPM on the highway in 4th) and the temps start slowly rising -- nonstop. at rausche creek two weeks ago, I crawled without much issue all day, but going up a steep access road with a little more rpm, it climbed from 200 to 210, to 225, and I finally shut it down at 235 (I'm using the digital temp sensor on my holley efi, so I'm not guessing as to the temp). I had no doubt it would have continued to climb (it hit 240 on the highway the day I got it back before I could pull over). I didn't let it boil over, but I haven't yet found a point where it levels off.. 240 is about as high as I dared let it go. I haven't let it blow the pressure cap yet (#16 cap)
 
jbsjunk said:
I leave my rad fan on in Summer. It'll range from 180 which is what the stat is to 215. I changed pullies to a 1:1 setup. The temp was scary before and the pump was overdriven. Been ironing out little bugs here and there but it's been my daily for four rears now.
Click to expand...

I have three spal "extreme" e-fans, and I have all three programmed to kick in at 180.
 
jmg222 said:
at idle and stop-and-go traffic, it sheds heat with no problem, so I don't think airflow is an issue. At anything over off-idle, say 1500 rpm or so, regardless of how fast or slow I'm going (2000RPM in 4lo in first gear results in same level of overheating as 2000 RPM on the highway in 4th) and the temps start slowly rising -- nonstop. at rausche creek two weeks ago, I crawled without much issue all day, but going up a steep access road with a little more rpm, it climbed from 200 to 210, to 225, and I finally shut it down at 235 (I'm using the digital temp sensor on my holley efi, so I'm not guessing as to the temp). I had no doubt it would have continued to climb (it hit 240 on the highway the day I got it back before I could pull over). I didn't let it boil over, but I haven't yet found a point where it levels off.. 240 is about as high as I dared let it go. I haven't let it blow the pressure cap yet (#16 cap)
Click to expand...
OK. Unless I missed it have you made sure the gauge is reading correctly.
 
Is it possible that your fans are set too low? When the fan is on and you are moving forward, the excess pressure built up may be reducing fan efficiency and allowing less air to actually move through the radiator. Effectively, you could be creating enough turbulence that flow through the radiator and fan is significantly impacted. Or, you are creating a possible high pressure zone inside the engine bay which would significantly reduce the effectiveness of the fan. This may explain why you don't overheat while crawling (fans moving all the air), but temp creeps up while driving down the highway and fans are on (turbulance/high pressure zone).

Try setting your fans to 205 and take it for a spin through the similar grades if possible. Worst case if it doesn't work, you can pull over and just change it back to 180 if you see no change. In my opinion though, 180 is way too low to set fan temp. Depending on your t-stat, that means your fan will constantly be on. I have an LS in my jeep with the same Novak radiator and fan setup, but my fans are set to turn on at 205 and turn off at 195. Going down the highway, the fans hardly turned on on a 95 degree day. The Novak radiator is very efficient at shedding heat.
 
gradon said:
Are you running cats?

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Click to expand...

Nope.


the_midwesterner said:
Is it possible that your fans are set too low? When the fan is on and you are moving forward, the excess pressure built up may be reducing fan efficiency and allowing less air to actually move through the radiator. Effectively, you could be creating enough turbulence that flow through the radiator and fan is significantly impacted. Or, you are creating a possible high pressure zone inside the engine bay which would significantly reduce the effectiveness of the fan. This may explain why you don't overheat while crawling (fans moving all the air), but temp creeps up while driving down the highway and fans are on (turbulance/high pressure zone).

Try setting your fans to 205 and take it for a spin through the similar grades if possible. Worst case if it doesn't work, you can pull over and just change it back to 180 if you see no change. In my opinion though, 180 is way too low to set fan temp. Depending on your t-stat, that means your fan will constantly be on. I have an LS in my jeep with the same Novak radiator and fan setup, but my fans are set to turn on at 205 and turn off at 195. Going down the highway, the fans hardly turned on on a 95 degree day. The Novak radiator is very efficient at shedding heat.
Click to expand...

I've been working through this with Novak, and I raised the same point-- but they felt the fans moving while I was at highway speed would decrease turbulence.

I'll try it -- the only reason I have low hopes for this is that it overheats at anything over 2000 or so rpm, regardless of how fast I'm going. going up a steep access road, in 4lo, second gear at 10-15 miles and hr sent the temps soaring.

I'm really starting to think the rad is just not flowing coolant properly. Latest from Novak is that internals may have rusted due to galvanic corrosion.
 
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