LJ70 Overheating Mystery: What have we missed? (1 Viewer)

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Jul 19, 2021
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This is my first post and I’m a first-time landcruiser owner (a life-long dream). Nice to e-meet you all.

Our little LJ70 is super fun & smooth to drive off road, but it’s also giving us overheating nightmares. Bought in 2020 and we’ve spent a year playing cooling system detectives and the temp gauge is still entering the red under minimal load.

We’ve scoured IH8MUD for ideas and have tried everything short of replacing the infamous 2LTE engine head. We know we’ll have to replace the head one day, we’re just hoping we don’t have to do it yet. (Especially if, like most of the things we’ve already done, it turns out not to have been the main problem.)

Does anyone out there have any ideas on what else could be the cause?

About the Victim:
  • 1990 LJ 70 (Prado), diesel, automatic, right-side drive, import from Japan, bought at 135,000km and have hardly been able to use it, used mostly for weekends/pleasure by previous owner.
  • Thermostat needed replacing when we got it and it had under-specced coolant. Not sure if it was previously being driven while overheating.
  • Drove it for a week on dirt roads before it suddenly overheated going up a minimally graded gravel road on a hot day and started madly leaking coolant out the overflow.
  • Doesn’t have the typical Toyota fan “roar” when you start it up (even after clutch fluid replacement), seems some folks on here find that either normal or abnormal (...?)
IMG_20200609_175337.jpg


About the Temp:
The temp shoots up abnormally high (even into the red) for short bursts of time, from 5-20 seconds at a time. Some drives there’s no problem; other times it keeps shooting up every 10 mins or so even in suburban driving conditions (especially bad during our recent Westcoast heatwave). Usually there’s a hill involved but not always. Not towing anything, no lead bricks in the back etc. We thought it could be related to inadequate revs, so we’ve been increasingly careful to turn off overdrive going up hills, and that seemed to help a bit but isn’t consistently preventing these temp spikes. Goal is to use this little beast for a lot more interesting off-roading than just trips around the neighborhood!

What we’ve done:
  • Coolant system:
    • There was massive coolant leaking but now we are 100% sure there are no more coolant leaks, thanks to the following:
    • Coolant cap: Replaced
    • Water pump: Replaced
    • EGR: Deleted
    • Cooling system: Flushed, no blockages, good flow. Sealed up some of the connection points that were leaking. Refilled with good coolant.
    • Fan clutch: Fluid replaced. Definitely stiffer after.
    • Radiator: Re-cored (it was ugly; before/after photo for entertainment below.) It does sit behind the A/C but surely it's not airflow that's the problem at this point.
  • Gauges:
    • Temp sender: Replaced
    • Temp sensors: Replaced
    • Thermostat: Replaced
    • Fuel Gauge: No issues with it (saw some people reported flakey fuel gauges made your temp gauge needle wonky, but our fuel reading is always consistent & seems accurate.)
  • Exhaust System:
    • No power issues, no black smoke. Little puff of black smoke if you hit gas at idle; but it’s clean after.
  • Other:
    • Fuel Injection Pump: Rebuilt. We thought we’d fixed the whole cooling system and got 2 blocks into the test drive to discover we were spitting diesel. No fuel leaks since this was replaced.
    • Oil: Replaced oil & filter, topped up oil (i.e. it’s not low).
    • Air filter: Replaced.

What we haven’t done: (Do any of these seem like they’d make more than a minimal difference?)
  • Could get new hoses (the current ones look fine; no cracks, and flow was good with flush)
  • Turbo: could clean intake
  • Rad output hose: could check the output temp (although we already know this is an issue so…); could get an adaptor to check temp of lower rad hose to see if coolant is still not circulating as it should
  • Exhaust Gas Temp Gauge: we have the connection installed, just need to set up the display
  • Engine Head Replacement :( :( :(

Engine Head Checks:
  • No hallmark bubbles visible when we pop the coolant cap
  • Overflow level stays consistent (since we got rad re-cored, new coolant, replaced clutch fan fluid, and had injection pump rebuilt)

Thank you for any help, ideas, or general commiseration!

Our rad before vs. after because I always enjoy seeing folks' horror pics on here. (Fins crumbled with a slight touch and there was coolant leakage at the seams too.)
1626736617998.png
 
I should add:
It's got a 2.4 turbo diesel engine (stock).

Engine light periodically comes on; code 11 and 12, which could be any of these, though I can't see how these would be immediately related to the temp problem:
11 Switch signal.
11 ECU/ECM.
12 Knock Control Sensor signal.
12 RPM signal.
 
The temp shoots up abnormally high (even into the red) for short bursts of time, from 5-20 seconds at a time
I would say this is from a cracked head Just a small crack most likely. The engine heats up, opens the crack slightly as it expands and allows some of the hot compression gases to leak into the coolant system.
What you have done so far is commendable, it shouldnt be overheating now and the head is the only thing left.

Have you checked the hoses when hot or cold to see how much pressure is in the system? Cracked heads often cause the hoses to stay hard overnight, really hard.

Ive had one of these on all my landcruisers. If there is something wrong you get an almost instant warning from the unit . The factory gauge is a bit slow to spike when it overheats. There is a nice spot just forward of the t/case shifter under the 7* series dash where it will fit.

1626741907262.png
 
Have you done a check for exhaust gas in the coolant? That's one of the first checks I'd have done.
 
Having owned one of these trucks for 10 years now, and towing a 16' camper every summer, I have had a lot of experience and challenges keeping my truck cool also. Here are my thoughts.

At the end of your post you say your coolant level in the overflow is now consistent. If this is true, then your cylinder head is fine. If your head was cracked, you'd still have the overflow filling up all the time, and air constantly in the system.

How many km's on the truck? If it's over 150,000km, I can pretty much guarantee the cylinder head has already been replaced.

I've done everything you have, and more. My engine still gets hot under load (only when towing mind you). I run Evans waterless coolant, so don't care that much. But the point is, these motors can still run hot under high load in high ambient temps. It's just how they are.

How thick was your radiator re-cored to? That has a really big impact on the cooling. I ran a 48mm for a while and it sucked big time compared to a 56mm I had before. I've now re-cored it to 64mm.

Do you hear your fan roar now? If not, I highly recommend replacing the fan hub with a brand new OEM Toyota one. If that fan isn't roaring, for sure you'll be seeing higher coolant temps.
 
I second the fan, you should hear this roar lots and lots, heck mine comes on so much I reckon I lose around 20hp each time but it never gets hot
sitting at a stop for at least 5 seconds, if you take off fast you will definitely here the fan and feel it, they move huge amount of air
 
I was having the exact same issues you have described above. It turned out to be the fan clutch and massive amounts of air in the system. The firs thing you should do is replace the Fan clutch with a new unit, then bleed the heck out of the system.
Also recommend installing a digital temp gauge, to me this is just as important as an EGT gauge. When i was getting air in the system my stock gauge would shoot up but the digital gauge would remain low, if it wasn't for the digital gauge i would not be able to diagnose it.

Good Luck
Keep us posted.
 

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