PT (non-Turbo) Runs Hot Pulling ~300lbs

[tcarlisle]

Hi All,

For the past month or so I have struggled with overheating. Have replaced everything, literally, having to do with the cooling system (list below) and I am convinced the cooling system is in proper working order.

While replacing the parts listed below, I ran across the gasket between the thermostat housing and cylinder head was breached, which contributed to the problem. But it wasn't the root of the problem, because after doing all the work on the parts below I can now say the cooling system does not leak.

The symptoms are that after about an hour on the highway with AC on, the temperature gauge goes about halfway, and returns to normal. But if you keep driving highway speeds with the AC on it will climb higher, to the 3/4 mark, and doesn't really come down, and I have to turn off the AC to get it to recover to normal.

Higher highway speeds (60-70mph) make the problem begin quicker and worse.... lower speeds (50-55mph) keep the problem at bay a little longer. Climbing hills exacerbates the issue.

Here is the kicker -- I don't see this issue unless I have a cargo carrier hooked up to the hitch I installed, and loaded down with ~300 lbs. My understanding is the PT is designed to carry 1,000 lbs, and the load in the cargo carrier plus occupants is not anywhere near that.

I suspect it might be transmission related at this point, and -plan to install a 2nd transmission oil cooler. I also plan to install a second electric fan (SPAL brand, will be in front of the condensor and pulling air in towards the engine. ), and I may seek out a larger radiator.

But I am wondering if this should be necessary. I am sure beefing up the cooling system will mask the problem, but I am wondering if it is a problem -- or maybe nothing is actually wrong?

The transmission never slipped or showed any signs of problem. It does have a very slow leak.

Radiator
Electric Fan
Fan Relays
Upper/Lower Radiator Hoses
Thermostat
Water Pump
Head gasket
Heater core was replaced last year, and I have bypassed it as part of troubleshooting to make sure it is not the issue)
Catalytic Converter (because it seemed clogged and restricted exhaust output)
I have purged some AC charge because it was thought to be possibly over charged. The condensor was very hot when idling, and purging some charge brought the condensor temp down.
There is no debris at all between the condensor, tranny cooler, and radiator.

[ptcruisersteve]

When you had the cylinder head off to replace the gasket did you have the head checked for cracks? Was the cylinder head resurfaced? If it was resurfaced was it rechecked to be flat? I would troubleshoot all other possible causes first before going in this direction if this might be a possibility.

Has a block test been done?

After replacing each engine coolant system related component was a coolant pressure test done?

When the temperature goes up to 3/4 does it fill up the coolant overflow tank?

Have you checked the hose from the radiator cap to the coolant overflow tank?

Did you verify that the temperature gauge is accurate when it does go up to 3/4?

Was your radiator replaced with a new radiator? What brand?

Was your radiator cap replaced? If so what brand and pressure?

What brand coolant did you put into the coolant system?

[tcarlisle]

The cylinder head was rebuilt by a machinist.

The block was not removed, but no cracks visible.

Radiator cap was replaced, the brand is stant.

Radiator is OEM, brand is what advance auto sells -- carquest.

Water pump is AC Delco.

Coolant was zerex g-05, but right now it is peak (because xerex was not available when/where it was last filled). It has a bottle of water wetter in it.

Temp sensor was replaced too.

The temp gauge hasn't been tested, but there is no reason to believe it isn't accurate. When the temp is higher than norm, the heater vents do blow hotter air than you normally would expect. I suppose I can validate it with a meat thermometer, but I don't think it will turn out to be inaccurate.

At this point, I am done looking for faults in the cooling system or engine internals, and am convinced the engine is putting off more heat than the cooling system is designed to handle --- for whatever reason.

If it never gets hotter than normal except with the additional weight, I suppose I can live with that.

There is no symptoms of dragging brakes, or pulley, etc.

[ptcruisersteve]

Originally Posted by tcarlisle

The cylinder head was rebuilt by a machinist.

The block was not removed, but no cracks visible.

Radiator cap was replaced, the brand is stant.

Radiator is OEM, brand is what advance auto sells -- carquest.

Water pump is AC Delco.

Coolant was zerex g-05, but right now it is peak (because xerex was not available when/where it was last filled). It has a bottle of water wetter in it.

Temp sensor was replaced too.

The temp gauge hasn't been tested, but there is no reason to believe it isn't accurate. When the temp is higher than norm, the heater vents do blow hotter air than you normally would expect. I suppose I can validate it with a meat thermometer, but I don't think it will turn out to be inaccurate.

At this point, I am done looking for faults in the cooling system or engine internals, and am convinced the engine is putting off more heat than the cooling system is designed to handle --- for whatever reason.

If it never gets hotter than normal except with the additional weight, I suppose I can live with that.

There is no symptoms of dragging brakes, or pulley, etc.

The block test is to check for combustion gases in the coolant system. This block tester can help diagnose unexplained engine overheating issues. With the amount of time and engine coolant related parts you have replaced I would recommend to have this done. There has been many discussions on many threads on this forum how after replacing the radiator the PT Cruisers stop overheating on the highway but come to find out later in some cases the combustion gases were slowly getting into the coolant system and after a certain amount of time it was determined that the combustion gases were getting into the coolant system.

Was the cylinder head checked for cracks?

Do you burp the radiator after draining and replacing the coolant?

[Handy_Cruiser]

Yep.

+1 on doing the chemical test to check for combustion gas in the coolant.

A partially blocked radiator can cause vehicles that don't otherwise overheat to heat up when pulling a load. But your radiator is reported to be new. And a cracked head or slight leak in a head gasket will sometime have these same symptoms. The chemical test should help detect this.

[rob342]

I think I'd be inclined to try another thermostat.

Maybe you drive more gentle/careful with your 300lbs behind the car, the rpm's stay boringly consistent, and the lack of flow variation encourages the thermostat to stick.

[tcarlisle]

I was able to duplicate the problem without the additional weight today, so whatever the root cause is it is getting worse and probably will make it easier to isolate the cause.

If the block were cracked and coolant was getting into the combustion chamber, the coolant level would not remain full. Since the replacement of all the parts in the list, the coolant level has remained full. Collant doesn't boil and overflow, etc.

I am not convinced it isn't the AC system. I don't think it cycles off -- ever. I have both high pressure and low pressure switches came in the other day and will replace. My AC doesn't have a high pressure service port, which makes it hard to test and ensure proper operation. Someone replaced the AC hose that is supposed to have the high pressure port near the compressor, with a universal hose that doesn't have the port. I might go to the dealer and get the right part and replace with the high/low pressure switches.

[tcarlisle]

I wanted to check in with an update. Block chemical test passed, so I drained the coolant from the radiator, filled with water, ran the engine, drained, filled, etc. until the only water was draining out. Refilled with Z-05. Still runs hot, but I can duplicate the issue without towing camping gear and driving 1+hrs -- I can just turn the AC on high and run it a little harder than I usually would, and it will run hot.

Somewhere along the way of all this, the check engine light came on with P401 EGR flow code. I wasn't paying that too much attention and was more concerned with the overheating, but I did grab a new EGV valve assembly and it didn't resolve the code. I had seen that before, a couple years back actually, and it turned out to be wiring (or so I thought). SO I wasn't really focused on this.

But then I thought why not focus on the code and not worry about the overheating, because the issues could be related. I replaced the EGR and the problem continued.

At this point I bought an ODBII USB cable and some decent software, to get a look at what the PCM sees, and it seemed to be running lean. Long Fuel Trim was 10-20% at all times, and short fuel trim was also adding more fuel. There were no codes related to the O2 sensors. I decided to replace the upstream O2 to see if it resolves this, and it did, and on a hard test run the temp only raised to 228, and then came back down to 215-220.

Prior similar test runs, the temp would climb to 230 and would not recover unless the AC was turned off it would stop climbing and come down a couple degrees, but never all the way back down until you got off the highway and were in low load driving conditions (meaning load percent < 20, not meaning not pulling load like this thread title says

But after resolving the lean condition, and then that very hard test run (WOT on the highway on ramp and hitting redline limiter) it only ran a couple degrees warm but stabilized when driving normal at highway speeds (with AC still on)

To be honest, I don't think I have ever driving the PT this hard so this might be normal. The PT just isn't my performance car.... when I want to drive hard I use my other car designed for that.

Going to take a long road trip today, driving normal, and doubt I will see any temperature issues.

In the midst of all that replacing of parts and tear down for a cylinder head, there was good reason -- it was loosing coolant for no reason that could be found. And of course the engine idles better and driveability is improved with a reconditioned head. But I was stumped once the coolant wasn't going down, at all, and still running hot.

Anyone that grew up in the age of non-computerized cars knows an engine that is running lean is running hot. But I would expect the PCM to throw codes related to this -- not an EGR code. I suppose it wasn't bad enough to throw mixture or O2 related codes, but that is a design flaw because it was running too hot and should have been throwing appropriate codes.

[ptcruisersteve]

P0401 - Insufficient EGR Flow

This code can trigger when you have problems with your engine under a load.

The computer in the PT Cruiser will trigger your P0401 code when it recognizes that there is not enough exhaust gas going back through the intake chamber. The PT Cruiser uses the oxygen sensor to monitor the air and fuel ratio in the exhaust as the engine is running. When the computer opens the EGR valve it will watch the 02 sensor signal. The P0401 code will trigger if it does not see the right change in the 02 sensor signal. This can also be caused by the 02 sensor not working properly.

Thank you for giving us feedback on the solution to this problem. Your 02 sensor most likely was on the beginning stages of not working properly when you started having this problem under a load.

[chuzz]

Yes, definitely a big thank you for the solution. I would have NEVER guessed an 02 sensor would make one run hot.