95 Suburban w/454 running hot

Plugged radiator.

230-235 when at a light. Then when I start to go again it goes back to about 220. When traveling at highway speeds it is a little above 220, when getting off of the highway it gets about 230. This is driving me nuts trying to shoot this trouble. My next step is pull the radiator and have it flow tested. Any suggestions will be appreciated. Thanks-Rob

Ya sure you have he right thermostat.?

you don't say how many miles you have on your truck, but I suspect if around 100k or over then you need to look at replacing the radiator fan clutch. While you are at it you might get a better fan-clutch fan from flex-a-lite. They make a 6 blade fan clutch fan which does a good job. You might want to make sure the radiiator is clean and there are no obstructions between the radiator and the A/C condensor.

What you describe sounds like you are not getting enough air across the radiator.

I would advise only purchasing an OEM fan clutch.... its been my experience that the GM fan clutchs work better than the rest.

I'm leaning with steve on this, they make 220 thermostats....

-The Lonely Grease Monkey

1985' K5 305CUI TH700R4 NP203 KJ's successor

"Ignorance is preferable to error; and he is less remote from the truth who believes nothing, then he who believes what is a wrong." - Thomas Jefferson

Ok, I took out the thermostat, radiator and water pump. I double checked the t-stat and it is rated 195 degrees. So, I am going to replace the water pump and the radiator. While I have all apart I decided to flush some freash water thru the block. After that I ended up with a block full of "tap" water, this I do not want. I couldn't find the drain plugs "lazy" so I got out this old electric pump I used to use for model fuel and hooked it up to my battery and there I sat.......... and pumped out the water very slowly........... when I got to the bottom I found all kinds of ....rusty muck? then it plugged my pump and killed it! Where are the drain plugs so I can do this right?

Off hand I'm not sure exactly where the drain plugs are but I can tell you where to look. The drain plugs on the engine block should be on each side of the block about half way back from the front of the engine. If you can locate the freeze plugs you should be able to locate the drain plugs. They are kind of hard to find....above the oil pan and below the cylinder heads, with a square head (If I recall correctly). IF you have such a mess you will need to flush the block as best as you can of the sludge so you don't have the same problem again. Be very careful with the drain plugs if you decide to remove them so you don't break them or strip the threads. I think I would try to figure out some way of flushing the block without messing with the drain plugs.

Its not a big deal to have regular water in the block, just compenstate for this when you fill the radiator with coolant to get close to a mix of 50/50 coolant to water. That sludge crap needs to come out of the block, do what you can.

Have you run strait water in the coolant system??? This promotes rust and problems with your freeze plugs.... also the radiator will "sludge up" too. Coolant does loose its properties over time, it does make sense to flush the cooling system every few years and replace the coolant / water mix with new.

Make sure your A/C condensor is clean and there are no airway restrictions in front of the radiator.

Well I replaced the radiator and water pump with exactly the same problem, I am starting to think I have a slightly blown head gasket. Before I rip into it I am going to check the timing.

sat..........

IS the fan clutch working properly...........?

From what you have said this problem is mainly happening at an idle

go borrow a coolant pressure tester or have it the truck pressure tested to make sure you don't have a problem.

It still sounds as if you don't have enough air coming across the radiator at an idle. Did you buy a good 3 or 4 core radiator..... you can't use a marginal radiator on a 454 at all.

I can't stress the importance of a good fan and a GM fan clutch.

One sign of a blown head gasket is coolant in the oil or oil in the coolant, another is excessive white smoke out the tailpipe.

some assumptions about the cooling system. WE assume the shroud is in good shape and not broken or missing parts, we assume the A/C condenser is clean and no airway restriction in front of the condenser or radiator, you have a new good thermostat, a new water pump and a new radiator.

do a pressure test and check the timing and see what you find. I know my truck (92 K 1500) with a 350 is very sensative to the correct base timing, if you are not right on the mark then the truck runs like crap.