Overheating issue

Tiny
DANGARYYOTA
  • MEMBER
  • 1995 TOYOTA 4RUNNER
  • 3.0L
  • 6 CYL
  • 4WD
  • MANUAL
  • 137,000 MILES
My vehicle had been running decently lately, however when taking it on trips longer than 1.5 hours, it would begin to run hot. The temp gauge on the dash would go up near the red zone, but then settle back to normal. It would do this several times for the next hour of the trip, but never actually overheat.

I was putting a few ounces of coolant mix into the radiator regularly to top it off, since I have a leak in my heater core that was dripping inside the vehicle.

We decided to investigate whether the issue was the thermostat acting up, and found out that the previous owner had removed it, and I have been driving it like that since I bought it a few years ago.

We put in a new thermostat and bypassed the heater core so I wouldn't lose coolant anymore. At this point, I road tested it, and it got hot and stayed hot after only 10 minutes of driving.

I was used to seeing coolant running left to right across the top of the radiator when I had been topping it off regularly. Also, there was a brown sludgy residue in the the coolant for a long time, and it often sludge up the overflow jug. I'm not sure what this sludge was, but our guess is that the previous owner had a leak at one point and used one of those leak-sealing tablets that dissolves into the coolant (supposedly).

Anyway, the coolant hadn't been running across the top of the radiator for a few weeks before we touched anything, so, fearing that the sludge had blocked up the radiator, we replaced it. When doing so, we completely flushed the whole system (in the block too) with a garden hose, and saw only a minimal amount of the sludge in the exiting water.

We also replaced the fan with a new one, since we thought maybe the clutch was bad on the old one and it just wasn't blowing enough air at temperature. We also checked that the secondary electric fan comes on when the A/C is on, which it does with no issues.

So with a bypassed heater core, new thermostat, new radiator, new fan clutch, complete system flush, and new coolant mix, I took it out for another road test. This time it lasted 15 minutes before actually fully overheating and blowing steam.

I don't have a lower fan shroud, but I know that's not the issue here. We don't know what to do next. Any takers?
Saturday, June 20th, 2020 AT 6:58 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Does the vehicle run normally other than this issue? Does the check engine light stay on when the engine is running? It almost sounds like it could be a head gasket related issue. Do me a favor, take a look through this link and let me know if it mirrors anything you have experienced and try to complete the tests.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know.
Joe
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Saturday, June 20th, 2020 AT 9:03 PM
Tiny
DANGARYYOTA
  • MEMBER
  • 2 POSTS
We recently replaced all 6 spark plugs, it got all new plug wires last year when there was a firing issue in cylinder 5 due to a bad wire, and we checked the distributor cap for carbon tracks, which there are none.

We put it on the scope because the idle is a bit rough (but not throwing a code, ) and cylinders 1, 3, 4, 5, 6's patterns are fine, but cylinder 2's pattern's firing line was really low, and the spark line has a lot of hash on it. We swapped wires for cylinders 2 and 4, and the problem stayed in cylinder 2.

We are not sure the two problems are related, and are going to do a compression test on 2. We also have a block check with test fluid and are going to check for exhaust fumes in the cooling system.
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Sunday, June 21st, 2020 AT 9:36 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Okay.

Do the compression test and check for a head gasket issue. Also, if the vehicle has a misfire, make sure the catalytic converter isn't damaged from raw fuel entering it leading to its creating too much back pressure.

I think you are on the right track with what you want to check. Let me know if you ever noticed a smell that may indicate an internal issue or fuel related issue. There are so many things that can cause the overheating.

Let me know what you find.
Joe
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Monday, June 22nd, 2020 AT 9:35 PM

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