Vannin' Home Forums Chevy Troubleshooting Help! G20 Van Overheating Problem

Good afternoon! I recently joined the vanning community with a 1990 G20 shorty (5.0). Since I bought it a few weeks ago, I've changed the oil + filter, spark plugs, thermostat, temperature sensor, belt + tensioner, air filter, fuel pump + filter, radiator + hoses. Despite all this, the van is still overheating. I know there was some serious rust in the cooling system (previous owner used tap water ), so I used Thermocure coolant system rust remover to flush out some rust before swapping the radiator. I could not find any signs of damage on the water pump, but that will probably be my next swap.

Any suggestions would be greatly appreciated!

Please post a picture of the water pump's impeller once you have it out.

How well does the heater work?

I've been thinking about adding an inline coolant filter, either on a heater hose or in the main hose to/from radiator, but they are not cheap.


https://www.jegs.com/p/Champion-Coo...-Inline-Coolant-Filters/3629311/10002/-1

I've seen cooling systems so bad with rust that the impellers of the water pump were almost completely disintegrated. Hopefully the cooling passages in the engine block aren't plugged up.

I just replaced the water pump and it’s still overheating . My driveway looks like an antifreeze bottle graveyard. The impeller didn’t seem to be bad.

[img]https://ibb.co/tYsdrCn[/img]
[img]https://ibb.co/P1Xf8Fp[/img]
[img]https://ibb.co/mqnKsN4[/img]

Balls,

Is the radiator /fan shroud in place, does the fan clutch engage?

What are you reading coolant temperature with?

My cash gauge now sometimes reads higher than usual. I thermo epoxied a K type thermocouple to the Intake manifold at the base of the T stat housing, then insulated it from fan's flow/ airflow. Did the same to the base of the radiator inlet.

Its rare that I go much over 197f even when dash gauge reads higher than usual.

Usually when slowing down off a freeway and stopping, it will climb towards 206f then lower again+.

Without this confirmation that it is not running too hot, I likely would have been stressing, but have done 4 X crosscountry road trips with that original temp gauge reading a bit high, sometimes.

Verify that the thermostat is opening, once the needle is around the middle of the temp gauge see if the top radiator hose is getting hot to make sure coolant is flowing through it.

You can sometimes get a bad thermostat new in the box or an air bubble is preventing it from opening properly.

My son's '87 Jeep Grand Wagoneer was overheating. He replaced all the usual parts and it didn't help. He just reset the timing and that fixed it. It was advancing too much. May not be the issue, but it's worth a try (since it's free and easy if you have a timing light).

Thank you all for your input! Sorry for the late reply, it’s been a long couple of days of troubleshooting and ripping out hair.
I finally took the van to a mechanic who charged me $120 to point out the temp gauge wasn’t working properly. I installed a $20 Bosch aftermarket temp gauge and I’m happy to say the engine is running cool under 180°.
I pointed out to the mechanic that there was a lot of heat radiating from the floor between the driver and passenger seats, and he said the catalytic converter is most likely backed up. I had every intention of removing it and soaking, but after a battle with rust, I chopped it off along with the pipes and muffler and installed a Magnaflow Glasspack muffler instead with the pipe coming out in front of the rear wheel.
To test out what I believed would solve my mechanical issues, I embarked on a 2 hour trip only to have the check engine light come on 40 minutes after getting on the highway. All the temperature levels were fine, however, when I stopped at a gas station, the van wouldn’t turn on for a good 20 minutes. The starter motor wouldn’t even engage. At this point I suspect I have a faulty starter, so I’ll probably be replacing that as well and adding a heat shield to diffuse some heat from the block.
Has anyone faced this issue?

Yep ... went to gear reduction starter and heat shield ...

A 1990's fuel/air ratio and spark advance, is controlled largely in part due to the input from coolant temp sensor. It is expecting a 195f thermostat installed. My brief foray into sub 195f thermostats yielded a 15 to 20% instant fuel economy kick in the balls, which returned when a 195f one was.



NOt sure about chevy but dodges temp gauge sensor is one wire( base grounded to mintake manifold) and can be purchased for under 10$



Go to battery (-) terminal. Is/was there tons of white corrosion here? how about green on the +?

Follow this thick cable to where it attaches to engine frame/starter base.

Remove. file/wirebrush shiny ring terminal washer , bare steel, screw/bolt threads retighten, cover anything shiny with axle grease.

Bad grounds cause many a weird issue.



Eliminate these potential culprits.

Battery Ground to engine/frame/firewall connections. Often overlooked, often declared fine when they are not.
Often the issue or a contributing factor, often a potential future issue, easily nipped in the bud before they can cause stress and a parts throwing marathon.

After a lot of troubleshooting, I learned the paperclip-in-OBD truck and got error code 32. I read that generally the EGR valve or the MAP sensor is the culprit, so I went ahead and replaced both. Now I’m in the Walmart parking lot waiting for the engine to cool down again due to the same issue. I’m clueless at this point.

Maybe carbon buildup in the EGR ports/tubes?
Seems that code is set when there is insufficient vacuum at the EGR valve.

That crossed my mind as well, so I made sure they were clear when changing the parts. I did find a bit of cracking on one of the elbows connecting to the intake, though I don’t see how it could affect the starting of the van. When I turn it off, the temperature slowly rises from around 170 to 190, then the van won’t turn on until it dips below 160.