91 Suburban 454 overheating when towing

[keith91]

New to forum to try to help my brother figure out what is going with a 91 Suburban 2500 he got. It has the 7.4 liter engine and is 2wd.

The problem is that it overheats when towing his boat. It seems to run ok with no load, but has always run hot according to the previous owner.

Things he has done to fix the overheating:
--took to 2 mechanics and they could not find anything except adjust the timing some. Head gaskets and block checked out ok.
--replaced the catalytic converter since this is supposed to be a known issue with it clogging
--replaced the clutch fan with a high capacity fan

Still overheats when towing. It will also backfire every now and then but does not do this frequently or continually.
Also, it seems it is low on power for a 454. When he replaced the catalytic converter he said it seemed to pick up a little more power, but still seems low for a big block.

I did a search on the forum and found a thread on an 88 suburban and some responses said to check the water pump to make sure it is the right model. He will do that and also see if there are any coolant air pockets, which was another suggestion.

Are there any other recommendations on what could be the cause? Or is there other websites that may have some info?

Thanks,
Keith

[biggbabysweetz1]

lots of things can cause this, first you may want to try the cheaper route and pressure wash your radiator and oil cooler (if equipped)
i have an 89 with the 350 and it liked to overheat cause the factory oil cooler would plug up with bugs and junk

also you may try a cooler thermostat. im guessing your running the standard 195 stat, try runnin a 180 or a 160 if you can find one.

[16th hippy]

to expand a little on bigs comments....if it has no external/aux trans oil cooler, then it could eb just the trans getting too hot itself, seen this alot when people tow stuff, but if fine with no towing. if no aux cooler present, then think about getting one.

[biggbabysweetz1]

Originally Posted by 16th hippy

to expand a little on bigs comments....if it has no external/aux trans oil cooler, then it could eb just the trans getting too hot itself, seen this alot when people tow stuff, but if fine with no towing. if no aux cooler present, then think about getting one.

good point, the tranny overheats too. i knew i forgot somethin

[keith91]

Thanks for the replies.

Help me understand how the tranny overheating causes the engine to overheat. Is it just the metal to metal contact between the engine and the tranny?

Thanks again.
Keith

[biggbabysweetz1]

in your case your radiator also acts as a tranny cooler, while the metal to metal contact between the trany and engine does transfer heat this isnt the prime point of an over heat. the tranny fluid can easily get up to temps of 300 or higher, in which case when it goes through the lines to the radiator it will transfer this heat to the coolant, the coolant then runs back into the engine warmer then when it left.
there are also auxilary tranny coolers that are specificaly designed to remove the heat more efficiently and quickly than an in radiator cooler.
if this burb has an automatic theres a 99% chance its got a in radiator tranny cooler.

[keith91]

Thanks bigbaby.

It does have an automatic. Will look into it.

Keith

[biggbabysweetz1]

heres a link to a tranny cooler available from partsamerica.com
http://www.partsamerica.com/ProductD...pe=895&ptset=A


this one is only 40 bucks and should improve the temperature of your tranny by a lot!b

[2000CAYukon]

The engine should not overheat even if the tranny does not have a tranny oil cooler (which you should add).

Was the water pump ever replaced? The impellar does wear out and could be your problem.

The lower radiator hose can collapse under a load and cause an overheating condition. The hose should have a piece of wire in it to prevent the collapse.

Make sure the condensor coils are clean and air can flow thru the condensor and radiator.

On my 90 K1500 5.7, it started to run warm as the air temp got warmer. After the side tank broke, I replaced the radiator and it never ran as warm as it would when hot. The radiator had lost some of its cooling capacity.

A backfire can occur from a lean condition which can also make it run hot. You should probably get the engine scaned to see if it running lean.

//2000CAYukon