Knock sensor / overheating ?? Clueless

[firebiz16]

I've replaced the entire cooling system on my 1995 3.0 4Runner and it still overheats while driving. It maintains normal temp if I just let sit and idle. If it heats up while driving, I can rev the engine to about 4k rpms and the temp goes back to normal.

Just wondering if anyone ever heard of a knock sensor causing overheating?

Found this from a Google search about overheating and knock sensors.

Too Hot To Handle
Too much heat is bad news for the engine because of the damage it can cause. One of the first symptoms of overheating may be detonation (spark knock). An audible pinging or rattling as the engine strains under load may be a signal that there’s too much heat building up in the combustion chambers. If the knock sensor is doing its job, it should signal the computer to re**** the timing, but it may not be enough to counter the heat. And even if it is, the engine will lose power and economy as the timing is backed off to counter the knock.

 

[turboSR5]

Your knock sensor is not the cause of overheating. That post is just stating that once the engine is over normal temps your more likely to ping and the knock sensor does what it does best, it narks on your combustion chamber to the ECU which then re****s the timing.

 

[mikedks]

I second turbo, knock sensor is doing its job by re****ing the timing when your engine begins to ping. Unfortunately, pinging, in this case, is the result of overheating.

Cooling system is pretty basic, should not be too difficult to diagnose. Here's the basics:
-radiator to disperse heat
-fan/fan clutch to draw cool air over radiator
-thermostat
-water pump
-radiator cap-pressurize system

Couple of thoughts, am assuming the t-stat is new as well as a cleaned and/or
flushed radiator due to you saying the system is all new. Don't think it's possible for the truck to run w/o the water pump. So let's look at what I understand are common issues with the 4 Runner:

-Failure of the fan clutch
-Air in the system
-Head gasket issues

-Also can't hurt to pressure check your cap, common fail item.

Yeah, I think its definitely the fan clutch, makes sense to me.

 

[firebiz16]

I have replaced the fan clutch, water pump, t-stat, new belts, hoses, valve covers, flushed and cleaned radiator, new plugs, wires, and distributor.

The problem is, it will idle for an hour and never overheat, I drive it for ten minutes and it begins to overheat. I can put in neutral, rev it to about 4k rpms and the temp gauge goes back to normal. Drive more and have to repeat the process. It acts like it not getting flow through the rad unless it's at high rpms under no load. I'm getting good hot heat in the cab also.

I guess I'm going to pull the rad today and take it have it checked by a professional. That's the only thing I can think of.

Also the HG were done about two years ago, I'm not loosing coolant and get no white smoke from the tail pipe.

On a side note, it does not seem to have any power, I know the 3.slow is not powerful, but it just seems dead, I think that may be the knock sensor throwing the timing off though.

Would a HG cause this type of overheat and cool down at high rpms?


Thanks for ANY MORE SUGGESTIONS....

 

[firebiz16]

I am by no means a mechanic, I'm just going on what I read.

Am I wrong that if the knock sensor is ineffective, it re****s the timing. This in turn causes excessive heat in the engine that the cooling system may not be able to overcome - thus overheating under load at low rpms...

Am I totally wrong? I'm just stumped with what would be causing this.

Thanks

 

[RockinRunner]

who did your waterpump & timing belt? if you have no power it's possible your timing is off. if flow is the issue maybe you have a defective WP or a massive airpocket in the system.

 

[BucknutBob]

Firebiz, I tend to agree with Rockin--you may still have a defective water pump. I know your knock sensor and your timing are NOT causing it to overheat--that's not how the system works. Like those earlier said, knocking and the resultant ignition change are CAUSED by overheating--they are responding to cooling problems, NOT causing them. Also, you never mentioned checking the radiator cap--if it's not holding pressure, your coolant will boil much sooner than normal. A weakened pump or a bad cap could conceivably keep up under light loads like you mentioned, but not be enough once you're pushing it.

 

[firebiz16]

I just went and purchased a brand new radiator and will install this afternoon. I'll let you know what the result is.

 

[RockinRunner]

Good luck.

Just a little rant... It kinda pains me to see people just throw parts at a vehicle. I understand not everyone is mechanically incline, or has the best diagnostic skills but please try your best to do proper research and feed out the bullskit and take the extra time to try to diagnose rather than throw parts at it.

In every concern on any vehicle, there can only be so many things wrong. I hate to see people piss money away when it's not needed. That extra cash can go toward something better ya dig?

Keep us posted and do check that radiator cap!

 

[firebiz16]

Ok, I replaced the radiator and new coolant this afternoon and it drove fine for about 30 minutes. Best yet. Then all of a suuden it started the same thing again.

I took a video of my temp gauge to show whats happening. Ever seen this before or can any one explain it.

Click or paste this link to see the video....

95 4runner temp gauge - YouTube

Thanks
Chris

 

[RockinRunner]

i would suspect a big pocket of air in the system. If not that than perhaps a failed WP.

 

[RockinRunner]

try jacking up the front end on jackstands to help push the pocket of air thru the system. I know this may sound a little unconventional but you can take a coolant pressure tester and pressurize the system a little to push the air thru.

keep in mind when you do this (BE CAREFUL) hot coolant is hot lol. I had a problem with a vw beetle and this method seemed to work for me. Also elevating the engine may help push the air thru the system.

How are you bleeding the air out of your coolant system?

 

[firebiz16]

I'm just letting it burp out on its own. Leaving the rad cap off and squeezing the upper rad hose every now and then.

I have added to new videos to observe what happens.

1. Video of radiator burping out. I guess this is just air. It seems to be alot of air if so. Does this mean anything else? I really don't know.
4runner overflowing radiator - YouTube

2. Video of exhaust pipe. Keep in mind it was 25 degrees F when this was taken. I'm not sure if its normal. This really does not look like the other videos I've seen of true blown head gaskets.
Possible blown head gasket 1995 4runner - YouTube

Thanks for all the input....

Chris

If I do have a blown head gasket what my temp gauge act like that. (previous video above)

 

[firebiz16]

Still having overheating issues. Went this morning to Toyota and bought the $28.00 T-Stat that has the jiggle pin. Replaced T-Stat and refilled with coolant. NOW, the darn thing over heats and will not cool down from revving the engine to around 3500 rpm. It now gets hat and stays hot, it boiled over this time, steam coming from everywhere.

NEW: Radiator, T-Stat, Water pump, New Upper Hose, Valve Covers, Belts, Fan Clutch.

The only thing I can think of is air in the system, If I have that much air in the system will it overheat and not cool back down from revving the engine.

I've read about the lower hose collapsing. Should this happen while idleing, driving or during cool down after the engine is off?

I get good heat in the cab so I dont think the heater core has anything to do with it.

Thanks Again.
Chris

 

[BucknutBob]

Not to be mean, but you could've paid for hours of diagnostic work from a professional and had your vehicle running again by now (and probably saved a lot of money, too). Do you always solve problems by replacing everything even remotely related to what you think is the problem? Have you even had the system pressure-tested? You're going to feel really dumb if all you needed was a new cap on your radiator. If you have so much money to burn, put the thing in a shop and tell them to fix it. Or just keep buying parts--you should have the vehicle replaced before too long. Friend, there ARE better ways to solve things.

 

[firebiz16]

I understand what you're saying, and no I don't have plenty of money, the parts I've replaced are still cheaper than 5 hours of mechanic labor.

My mechanic replaced everything except for the T-stat and radiator. No I have not had the engine pressure tested, although I didn't mention it, but I replaced the Rad Cap too.

I just discovered a small hose was leaking on the back side of the motor. The clamp was not where it was supposed to be. It was dumping coolant on the back of the block and steaming there. I fixed that and it had no effect on the overheating.

 

[Thisismehere]

It could be a clogged cat

I guess it’s too late
But a clogged catalytic converter could be overloading your engine