1988 GMC Vandura 5.7L Weird Overheating Issue (A-Team Drift Van)

[VanGasm]

Hi Team,

Been a while, but we got delayed on the A-Team Drift Van project from last year. Got solidly working on it over the last month and have a super peculiar overheating issue. I'll put the list of mods below, but I have a feeling this is a super simple issue (duh moment) that one of you can help resolve.

You must be registered for see images attach

Van runs amazing with one small issue that's driving me f*cking crazy on my initial light road testing. When driving at highways speeds on uphills, the temp gauge spikes to 240-260 in about 15 seconds. I'm hyper conscious of the motor and gauge and found a little trick to resolve the issue immediately. I drop the motor to neutral, turn off the ignition, coast, wait a couple seconds, then fire the engine back up, and the gauge immediately slams back down to 160 and generally holds for the remainder of the hill, flat ground, downhill. Temp holds solid for 10-15 miles, then does it again on the next little long uphill. Do the same, non-preferred rolling shutdown procedure--problem fixed.

I've driven with the doghouse off and had a laser temp reading on the thermostat, solid between 160-180 while the gauge is showing 240. The motor as far as I know isn't overheating and water is flowing. I haven't invested in rear end modifications (gear down and posi) as I'd like to get this issue resolved first. With a TBI motor, there are a variety of things that concern me and hoping you guys can help out.

Since this is being built to drift, I need to keep this thing cool.

My initial thought is that I just have an air bubble caught somewhere in the system. I've kept an eye on the coolant and over the past full warm/cool cycles, it's sucked down about 1/4 qt of fluid in the reservoir last night. I'm going to test run it today and see if the issue resolved itself... but I think it's deeper than that.

My Ideas on Potential problems:
-Some dickheaded bubble in the system
-Pinhole leak in head gasket on temp sensor side (grabbing test kit this morning)
-Water pump pulley/slipping. Had a pinhole transmission cooling line leak that sprayed fluid on the front of the motor. I cleaned everything up, but maybe the fluid interacted with the belt material and it's just not creating enough friction on the smooth pulley anymore. (grabbing new belt and brake parts cleaner this morning)
-Something going on with the timing/injection under load. I thought this might be a potential issue cured with the rolling restart.
-Something with the old gauge and or wire to the temp sensor.

Motor Mods: From front to rear.

-10" electric fan on front of the radiator. Placed top/driver side below the radiator inlet. Constant on with ignition.
-New stock radiator (shroud still installed)
-Performance flex fan (properly mounted at the right depth in the shroud)
-New water pump (Not the best pump. As a crossover year, the part number kept producing standard rotation water pumps. Went through 5 pumps at three parts stores to have them give me a reverse rotation water pump. Budget version. That said, I'm only doing highway driving with this now and it shouldn't be having this issue.)
-New Hoses
-New Radiator Fluid
-New Block Temp Sensor
-160 Thermostat
-14" x 3 in tall air cleaner
-Trans-dapt Swirl torque TBI Spacer
-Harris Tuning Stage 1 Chip
-New O2 Sensor
-New 2.5" exhaust system to X-Pipe, then to 2xFlowmaster Super 10 exhaust. No Cats.

I'm about to grab the keys on go out on another test run, but hoping you guys could throw ideas out there in case my ideas above aren't spot on. Thanks everyone!

 

[PlayingWithTBI]

I've driven with the doghouse off and had a laser temp reading on the thermostat, solid between 160-180 while the gauge is showing 240. The motor as far as I know isn't overheating and water is flowing.

I'm confused, is it overheating or not? Your IR gun say no. Put a scanner on it and see what the CTS next to the Tstat tells the PCM? I'm thinking you have an issue with your wiring from the CTS in the head to the gauge?

 

[VanGasm]

Thanks. I'll check that.

 

[VanGasm]

End of Day update: The engine is definitely getting hot. I was concerned of a blown head gasket, so I bought a block test kit. Drained the radiator a few inches, got the engine to temp, then conducted the test. Did it four times. No change in color on the fluid--indicating no head gasket leak.

Disconnected the wire going to the CTS on the driver's side of the block. Grounded it and the gauge pinned to the 260+ position as designed. Held it there for a minute with the engine running. Did not waiver at all. Reconnected the wire. Gauge immediately went to operating temp. I pulled the wired from the loom, inspected for cuts/grounds... nothing. Cleaned off the connectors and reassembled everything in a clean manner.

I cracked the radiator cap half way and took it up my test loop hill. The temp climbed to 240ish, but then slammed back down again before the crest of the hill. Bubble? I did another lap or two and it still heated up, but not as much. Pulled over and checked the radiator fluid and it lost about a half gallon in the system from the loose cap and driving OR I really did burp a bubble out of the system.

Swung by Napa thinking my problem could simply be a malfunctioning radiator cap. My parts guy at Napa used to be a shop owner and took a few minutes to look at it in the parking lot. He's convinced it's either a head gasket or a flow issue. So, I drove it home (2 blocks) and check the flow due to the water level being low. Flowing correctly from the driver's side to the passenger side at a healthy rate. Conducted another block test with the blue fluid. No change in color.

Filled it back up, attached the cap, then took it on a longer test loop. Climbed again to 240, then back down to operating temp.

So... This thing is driving me f*cking crazy. I'm going to let it sit for the night. Hopefully, I purged the bubble from the system with the loose radiator cap. Maybe it will cool, equalize with the coolant reservoir, and all will be well.

NOTE: The Napa guy said my radiator looked thin. I laughed and told him that was the one he sold me as a replacement to the original. We both scratched our heads. What are you guys tracking for the thickness of a standard g2500 radiator?

 

[PlayingWithTBI]

I'd still check to see what the ECM is seeing.

 

[VanGasm]

I'd still check to see what the ECM is seeing.

Total noob question, but what equipment would I need to check the ECM?

 

[PlayingWithTBI]

An OBDI scanner, like the Snap On Red Brick, a laptop with the correct app, etc. You can put a DVOM on it and check resistances too but, that's kinda cumbersome while driving down the road.

 

[454cid]

-Performance flex fan (properly mounted at the right depth in the shroud)

I would think this would be more of a low speed issue, but I'd suggest a real fan, or a well done electric is this is really a track vehicle.

-New water pump (Not the best pump. As a crossover year, the part number kept producing standard rotation water pumps. Went through 5 pumps at three parts stores to have them give me a reverse rotation water pump. Budget version. That said, I'm only doing highway driving with this now and it shouldn't be having this issue.)

Maybe take the rear cover off, and verify it's reverse rotation, if you know what to look for? If both were used that year, maybe it was mis-boxed and you've got a standard rotation pump.

-160 Thermostat

Is the ECU programed for this?

 

[VanGasm]

I would think this would be more of a low speed issue, but I'd suggest a real fan, or a well done electric is this is really a track vehicle.



Maybe take the rear cover off, and verify it's reverse rotation, if you know what to look for? If both were used that year, maybe it was mis-boxed and you've got a standard rotation pump.



Is the ECU programed for this?

I've got a good performance flex fan on it AND a big electric fan constantly running on it. New Radiator. The engine runs at temp the majority of the time and has this intermittent overheating issue going slightly up-hill. No bubbles in the motor that I can tell. Fluid is flowing correctly. It's weird.

As far as the thermostat and ECU, I'm going to hit up the chip manufacturer on this.

As for the reverse rotation water pump, I went through 4 "Stock replacements" sent to me that were standard rotation. I inspected the impeller by removing the rear cover. The 5th one found at an Autozone was a true reverse rotation.

Thanks for the help!

 

[L31MaxExpress]

I've got a good performance flex fan on it AND a big electric fan constantly running on it. New Radiator. The engine runs at temp the majority of the time and has this intermittent overheating issue going slightly up-hill. No bubbles in the motor that I can tell. Fluid is flowing correctly. It's weird.

As far as the thermostat and ECU, I'm going to hit up the chip manufacturer on this.

As for the reverse rotation water pump, I went through 4 "Stock replacements" sent to me that were standard rotation. I inspected the impeller by removing the rear cover. The 5th one found at an Autozone was a true reverse rotation.

Thanks for the help!

The flex fan is probably your issue entirely. Vans and flex fans or electrics generally do not get along well together. The flex fans flatten out as the RPM increases and will not pull enough air to cool the engine. An 18" flex fan is rated to cool a 4.0L engine without ac. Electrics have ok cfm at idle but nowhere near the CFM a good clutch fan can pull. Get an 11 blade pastic fan and a proper clutch and put it on there. A factory shroud should also be in place. A factory small block G-van prior to the front end update in about 1992 was a 28x17x1.25" core. With a proper functioning clutch fan my 83 stayed cool even with the ac cranked up and a trailer behind it.

I have also seen several fans installed backwards or were the wrong rotation. At idle they stayed cool and cruising at moderate speeds they overheated. At high speeds like 70-80 mph they cooled fine. With the engine running make sure the fan is pulling air and not pushing air. I worked on a 5.0L Mustang once that the owner had been fighting an overheating issue on. It was winter time in Texas. I changed the thermostat, verified it was burped and coolant was flowing. Ran it several hours and then took it for a test drive at highway speeds. It ran cool and I though all was good. It comes back in around May. It was overheating and the ac had popped off the high pressure relief valve and let alot of refrigerant out. So I ask question and fibd out it overheats at about 30-50 mph around town. AC had been cold at idle and warm at the same speed. Anyway I get it in the bay of the shop. Go over some stuff. I evac and re harge the ac. Get the car up to temp. Now it is in the mid 90s in thr shop and I have shorts on. As the car warms up, I suddenly notice hot air is blowing against my legs. It had a CW rotation flex fan on a CCW rotation pump. The car was cooling ok at idle when it was stationary but the fan was causing airflow to stall in that 30-50 mph range. When driven faster the ramming effect of the air entering the grille overcame the flex fan and cooled the car.