1997 Cadillac DTS Chronic overheating

OLDCARGUY56

MEMBER
1997 CADILLAC DEVILLE DTS
V8
FWD
AUTOMATIC
140,000 MILES

Radiator and all hoses preventively replaced over 1 year ago and no overheating problems observed. During long trip to Florida from St Louis in June engine overheated in Georgia. Thermostat, water pump and coolant replaced and arrived in FL without further incident. During return trip to St Louis, experienced overheating again, replaced overflow tank cap, which failed pressure test.

Now the engine is losing coolant again; during a recent 2 hour trip to southern Missouri, again overheated and needed to add 2 gallons fluid to fill! No evidence of any external leaks and no evidence of headgasket leak as exhaust is dry. Did observe that there is evidence of coolant flow through the overflow tank drain hose, although there is never any fluid loss actually observed.

I'm stumped! What have I overlooked or misdiagnosed?

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

If its not leaking than its burning in the combustion chamber. Have you check the engine oil condition?

You might consider block and pressure tests

Have it block and pressure tested-do the block first to pinpoint a combustion leaking into the cooling system or a gas analyzer to sniff for hydrocarbons at the radiator fill neck.

Pressure test: do not do a pressure test if there's leakage at the headgasket this might cause coolant into the cylinders and lock it up or bend a connecting rod if cranked thereafter. The headgasket should be repaired before doing the pressure test.

If the block and pressure test passes check the following: ,Pressure test the Rad. cap,Clogged radiator,air lock in the cooling system ,Fan clutch,Radiator electrical fan,collaspe hoses,water pump

Are the cooling fans coming on when needed/radiator not clogged-up-could be the high/low speed control of the computer see below