xpress

"MY 89 auto. Car starts to overheat after about half an hour driving at highway speeds - has been a problem which I have been working on. I think everything has been addressed except a new radiator. Work that has been completed:
1. new timing belt and water pump within the past 1000 miles.
2. new thermostat with front and back seals.
3. new antifreze with water wetter added.
4. hoses burped many times.
5. no leaks in system at all.
6. area cleaned out between radiator and A/C condenser.
7. front vents wired open with relay removed.
8. fans both are strong and work as they should.
9. no blockages in system.
10. new temp sensor installed.
11. heater valve wired closed.
The only deviations from stock are no belly pan and the heater core has been bypassed. The following temps were taken just when the temp gauge showed red:
1. waterbridge - 205, 2. top radiator hose - 215, 3. bottom radiator hose - 180, 4. top of radiator - 170, 5. bottom of radiator - 180, 6. coolant reservoir - 180, 7. cam covers - 200.
Does it sound like a new radiator is needed? I appreciate any comments that would help".

Spoke to Tom at 928 International who asked if I had a front spoiler on the car - car does not have one. He indicated that this probably was the problem as the air flow was not being directed to the radiator and they have seen this issue with other cars. Ordered a front spoiler - hope this cures the problem.

76FJ55

your temp measurements are a little od at the radiator. one thing to remember is that these have a cross flow radiator, inlet tank on passengers side and outlet tank on drivers side. When measuring the rad temps it would be much more informative to give the respective end tank temps as opposed to top/bottom readings.

fraggle

Check the flaps and the plastic spoiler at the base of the slots in the front. Sometimes the spoiler will get caught by airflow and flip up at speed but look fine at rest.

mark kibort

could be water pump too. any noises?

check the vents from being able to close. I had that issue, but mine had the motor removed.

If the radiator is hot top to bottom, it could be the water pump not producing the flow, or a bad seal behind the t-stat.

keep on investigating.

mk

xpress

1. Has a new seal behind thermostat.
2. Flaps are wired open - cannot move.
3. no noise from water pump, it's new. Water is being circulated.
4. Will take temps from both sides of radiator this weekend.
Could it be a bad radiator?

shmark

Is the 180 on the lower hose at the radiator or at the thermostat? If it's at the radiator it sounds like the thermostat is working and a 25 degree drop is pretty good. Engine operating temp is supposed to be 195 and it sounds like you're right there. Are you certain your temp sensor is operating properly? FWIW your temps look exactly like mine and I run center-gauge at highway speeds in 90 degree weather, slightly higher with the a/c on. Sounds like a bad sensor to me.

dr bob

Heater core bypassed means water flowing around the radiator. Consider almost completely blocking rather than bypassing if you are not going to fix it.

xpress

Dr. Bob,
The heater hose after the heater valve is now connected to the return hose that would normally come from the heater core, bypassing the core altogether. If I wire the heater valve closed would this help or does it make any difference? Spoke with Roger and he is sending me a new temp sensor to see if there could be any changes in the gauge readout - if the same, he suggests pulling the radiator and having it tested for blockage.

dr bob

Wiring the valve closed will certainly help. The heater core receives water from the rear of the heads (hot pretty soon after start-up) and returns it without passing through the radiator.

Lizard928

block off the heater valve instead or the coolant is bypassing the head.

xpress

New sensor installed - has made no difference in the gauge readout - still right at the red mark. Have wired the heater valve closed and this has also made no difference. The temps shown at post #1 are still valid after two recent drives. Hate to spend money on a new radiator but don't think there is much left to consider.

docmirror

If you have 180F coolant being delivered to the engine, and it's coming out at 215, I think you're rad might be clogged. Before replacement find out if you can try to have it rodded out. You'll need to find a shop that can R&R the end tanks with new seals. It's possible that some PO in the distant past had a small leak and put a can of stop-leak in it. That will clog things just as you're describing.

My Mondial had the very same symptoms, it would take about 20 min of spirited driving and the temps would go up to 200 and not come down. It was just heat saturation. I had the rad taken apart and rodded for about $130(new rad was 1200) and now it works fine in all weather. Note; Do NOT accept a 'backflush'. That will only remove part of the gunk, it has to be disassembled and rodded clean.

Tommy928

I assumed the thermostat is installed correctly and not backward?

xpress

Thanks Doc - the car is going into the shop to have the radiator pulled and rodded. Will post the results.

mark kibort

I use the bypass technique, vs blocking the heater core paths. Its worked fine for 10 years plus of hard racing in all temp conditions. sounds like radator issue. good luck!

mk