Overheating 350 FI V8

[Widow]

I have an 89 GMC Suburan with a 350 FI V8 which is overheating. So far we have replaced the water pump, thermostat, radiator hoses and radiator cap.

When on the highway with a steady acceleration it overheats, but as soon as you let off the accelerator to slow down...the temp drops.

I am looking for any suggestions as what to check next as we are getting fairly frustrated.

Thanks, in advance, for any help you might be able to provide.

[clipity]

I just went through the same thing with my89. I had bought mine used, the 89 that is and the P O had the wrong fan and sending unit installed.

Hope this helps Derreck.

[gchemist]

Have the radiator acid cleaned. Then add some Water wetter from www.jcwhitney.com.

[Jonboy]

you might want to check the fan clutch as well.

[Grim Reaper]

Originally posted by Jonboy
you might want to check the fan clutch as well.

If the heat problem was in traffic then yest the clutch fan would be high on the list. hwyspeed it's not the problem.


Here is the deal and it may be a free fix.

The fins in the A'C condensor are spaced wider then the fins in the radiator. Bug guts get packed in pretty bad.

Take the top plate off that retains the radiator. Garden hose from the fan side and see how much crud you can flush out.

If that doesn't fix it then yank that radiator and have it rodded or replaced. www.radiator.com and www.radiators.com both Have good prices on Modine's.

I had this same issue last year and Just bought a new Modine 4 coor and it cured the problem. In my case I had a lot more deposit's inside then I thought I did. PO did not change the fluid and flush. Coolant should be replaced every 2 years.

The gage isn't cycling from pegged and back is it? that's a different problem.

[Grim Reaper]

Ohh yeah..On engine problems like this I would post in the main 73-87 section. It see's more traffic so quicker responce.

[sierrasports]

same make model here:

i just replaced my radiator due to it ruined my transmission!

the radiator cools both the engine and transmission on your model. the lines on the tranny get crudded up because they ar the lower lines off the radiator., i think..

anyway, my motor stayed cool unless i got it over 55, and even then , it really didnt like overheat get hot, but it made me watch the gauge. but the whole time i was driving it, i was ruining my tranny.

now i have a brand new tranny and a band new radiator with new hoses...problem solved!

[KSSeverance]

My wife's 89 was attacked by a kamikaze bird that wound up driving it's head through the fins and creating a slow leak. We didn't know til about mile 1100 of the 1200 mile move we were making. Anyway, I went the upgrade route. I ordered a Howe Racing aluminum radiator PN 342E from http://www.summitracing.com/ and got a stand alone trans cooler with a 30k+ GVW. It went together in about 2-3 hrs and the only real mods were the trans cooler lines and a couple of brackets to move the fan shroud about 1/2". It has been running cool ever since. Even in 100 degree weather it sits right at the thermostat temp. The cost was about the same as a recore and the performance is alot better. Some things can be improved on a Chevy.

[sierrasports]

that was a hard headed bird....