Overheating... STILL

[Kinslayer]

Not sure if you tried this, you didn't specify in the original post but..
Have you tried changing O2 sensors? They regulate stuff like fuel air mixture..they can make your truck run rich (although if you're running rich your motor should run COOLER, not hotter)

Oh, and I think the problem isn't releasing the heat efficiently as you've already replaced everything to do with that, I think it's the fact that your motor is GENERATING too much heat.. The stock cooling system is more than capable of keeping the motor cool, most people have heat issues because they arn't running the right gearing for their size of tire they are running and expecting the truck to perform the same way as stock. Also, your tranny heats up a LOT when climbing in overdrive.. this would heat up your motor via heat transfer..

 

[Kinslayer]

FYI I think your tires/gears are fine (33s/4.10) so that's not the issue.

 

[Ecomike]

I have considered the O2 issue, but mine only has about 20,000 miles, 2.5 years on it. If it is my O2 sensor, that it is a drift in accuracy problem, or wiring or computer resistor drift problem, as mine is a Renix, it uses a resistor bridge circuit in the computer to measure the O2 sensor resistance (Resistance varies with O2 concentration on mine).

Mudderoy has an O2 sensor that puts out a variable voltage in response to O2 concentration.

I have checked my O2 readings at the sensor and is running just a tiny bit lean, and gas mileage is up some, but that could be from it's running hotter.
Chicken or the egg issue. Is it running hotter because it is leaner, or is running leaner because it is hotter?

Both of ours are getting to hot just parked with AC on, IMHO.

 

[Tenny]

Ok, so I haven't done anything to mine, it's been pretty much sitting in the front, and my friend convinced me to finally do a compression test ( i think i was very worried / didn't want to...)

Front
1. 145
2. 131
3. 125
4. 140
5. 132
6. 125
Back

So obviously the numbers aren't the best (I don't think it's too bad for 171k), but that's within the range of 120-150 of what I've heard is desired. I heard that within 10% of eachother is ideal, but 20% is acceptable.

So with that info there, I gather it's not a bad head gasket correct?

The nexted planned upgrades are New High-Flow Water Pump & ZJ Fan Clutch... once I get more money that is...

 

[winterbeater]

Since you guys are really getting scientific about this, what about defining the problem in measurables? One I'd be curious about is: What is the temperature drop across the radiator at idle? This could be measured with IR between inlet and outlet of radiator and compared between cooling systems that work and one's that don't. Major variable in that case would be radiator efficiency, but that could also be affected by speed of coolant flow. I guess AC on/off is another variable.

 

[Mike Axle]

I am not convinced a hi flow water pump will help at all. I have one and I also have hi temp issues. There is a break even point where the coolant is moving too fast through the rad and is unable to give up enough heat. What I mean is if the coolant moves too fast through the rad the coolant is not exposed to the air moving across the rad for a long enough period so the coolant temp won't drop enough. I talked with many guys on the Divide Ride and elsewhere, there cooling systems were stock. They had no problems. I have dual electric fans, aluminum rad and hi flow water pump. They had no problems at all without even so much as a fan overide switch. It took everything I had to keep temps under control. Through talking to alot of people I have been led to belive that installation of the thermostat is not as straight forward as we think. It must be immersed in coolant through out the burping process. The stat can be ruined in about 20 seconds of running dry when warming up the engine trying to get the stat to open so you can add more coolant. People I talked with have added a back flush tee in the heater hose line which runs into the stat housing. They add coolant directly into the stat housing too prevent the stat from cooking itself and making it almost usless. Like you I have not found the complete answer to this problem. Hope this helps.

 

[Ecomike]

Ok, so I haven't done anything to mine, it's been pretty much sitting in the front, and my friend convinced me to finally do a compression test ( i think i was very worried / didn't want to...)

Front
1. 145
2. 131
3. 125
4. 140
5. 132
6. 125
Back

So obviously the numbers aren't the best (I don't think it's too bad for 171k), but that's within the range of 120-150 of what I've heard is desired. I heard that within 10% of eachother is ideal, but 20% is acceptable.

So with that info there, I gather it's not a bad head gasket correct?

The nexted planned upgrades are New High-Flow Water Pump & ZJ Fan Clutch... once I get more money that is...

You did not say if those were dry or wet tests, hot or cold engine, idle or WOT on the throttle body. With those numbers I would add a product called Restore to get the compression back up on the lower ones.

 

[Ecomike]

Since you guys are really getting scientific about this, what about defining the problem in measurables? One I'd be curious about is: What is the temperature drop across the radiator at idle? This could be measured with IR between inlet and outlet of radiator and compared between cooling systems that work and one's that don't. Major variable in that case would be radiator efficiency, but that could also be affected by speed of coolant flow. I guess AC on/off is another variable.

As you know, I have already done this in several threads. I typically get a 30 to 45 F delta on the 2 row aluminum rads (copper fins, plastic tanks) I have in my 87 and 89 currently. But as you pointed out back pressure from a partially clogged radiator and water pump wear, age, brand can affect flow, which will affect the delta T.

Air flow will also affect the delta T!

 

[Tenny]

You did not say if those were dry or wet tests, hot or cold engine, idle or WOT on the throttle body. With those numbers I would add a product called Restore to get the compression back up on the lower ones.

Not sure what wet means... I think I read something about adding oil to it, and that was not done

The car was warmed up and it was WOT on the throttle body.

 

[winterbeater]

As you know, I have already done this in several threads. I typically get a 30 to 45 F delta on the 2 row aluminum rads (copper fins, plastic tanks) I have in my 87 and 89 currently. But as you pointed out back pressure from a partially clogged radiator and water pump wear, age, brand can affect flow, which will affect the delta T.

Air flow will also affect the delta T!

But the basic equation is that the delta T from the coolant passing through the engine is exceeding the delta T from the coolant passing through the radiator. Without rereading everything, and thinking that either the 87 or the 89 works good and the other one doesn't, can you identify which delta T is worse? Radiator or engine?

 

[Ecomike]

But the basic equation is that the delta T from the coolant passing through the engine is exceeding the delta T from the coolant passing through the radiator. Without rereading everything, and thinking that either the 87 or the 89 works good and the other one doesn't, can you identify which delta T is worse? Radiator or engine?

My 87 has gone from running cool to running hotter. The 89 has gone from running hot to running cooler, both in the last 3 months, with no real changes done by me during the time they changed. I suspect it may be something like drift in the O2 sensors, one running leaner, the other richer. I also still need to check for an exhaust leak on the 87, possibly blowing on the block?

The 87 has a 4 year old radiator, the 89 a 6 month old radiator. Same brand, same radiator. Same everything else. But the 89 is a much stronger engine, half the know, odo reading, miles. The 87 has the ZJ clutch, new, the 89 has 6 month old xj clutch, and the 89 still runs cooler. Note that the 89 ran hot when I bought it, had exhaust leak, crack, and a blown head gasket between #4 and #5 cylinders, but no coolant or oil problems.

The new (89 versus 87) radiator is giving me about an extra 5 to 7 degrees F delta T drop, so I have no doubt the 4 year old radiator is not working as well as it did when new. That observation is based on both engines at idle, and both engines at roughly the same temperature.So at equilibrium the 87 gets about 15 F hotter than the 89, both with AC off, at idle.

The 87 is getting a new CSF, all copper/brass radiator this week, which should make big difference. Also putting in the 97 parallel flow style AC condenser to replace the old 22 year old serpentine style condenser
in the 87. When that is done, the 87 may run cooler than the 89.

 

[Ecomike]

Not sure what wet means... I think I read something about adding oil to it, and that was not done

The car was warmed up and it was WOT on the throttle body.

If an injector is leaking or stuck open it washes the oil off the piston and rings, and lowers compression test results. People usually rerun the test on low pressure cylinders after adding about 5 ml of oil.