Hello Hello! I have a 1995 c4 with an overheat problem. She runs great on highways and interstate roads, but the second she slows down for town the temperature shoots up and she boils over. I have intermittent heat, but for the most part she's just blowing cold air. The fans don't come on without AC until about 220-230.

Here's what I've done to is since I bough it.
-Properly vacuumed and pressurized the system to find any leaks. Found two, fixed them. She holds pressure and vacuums between 25 and 30 PSI perfectly.
-Replaced the coolant relays.
-New 180 thermostat.
-new exhaust/no cats
-new oil pan gasket
-Replaced all main and rod bearings.

The only things I can think it would be is A. Radiator is gummed up and needs to be cleaned. B. Water pump is bad.

 

did you clean between the radiator and the condenser?

 

could be fan switch

 

I think that's normal . I switched the fan switch on my 84 so that it comes on at 205 and off at 185. easy to do

 

If you didn't take the radiator out and clean the fins properly,,,,,

 

Boiling over at 220-230? That screams radiator cap.

 

Not boiling over, that's the temp when the fans come on.

 

You should clean the AC condenser fins also. It catches all the stuff first. Also check your plastic tanks on your radiator for leaks while you have it out.

 

This is classic not circulating coolant. Almost always caused by lack of coolant, or air pockets, but based on what you've done, that seems unlikely. If you can confirm it's full of coolant and bled, then I'd be looking at the water pump, and checking radiator temps when it's idling and on it's way to getting hot.

 

I have not! The plan is to take it to a shop and have them clean the whole system.

 

Not to beat a dead horse but on your 95 the fans are NOT supposed to come on until the digital display hits approx 228 F at which point both fans come on a low speed; after only a 5 degree drop the fans turn off. If the digital temp get up to 237 F then both fans turn on at high speed and drop to low speed after a 5 degree drop.

As you have noted if the AC is turned on both fans come on at high speed by default.

The radiator needs to have the dirt between the fins removed via pressurized air or water blowing from the rear of the radiator out to the front. This is best done by removing the radiator.
It is possible that the water pump impeller needs to be replaced.

 

GUYS.


He is saying he's having overheating issues....in conjunction with variable to no heat from the heater. While he MAY have a fouled up radiator, no amount of debris is going to prevent the heater from making heat. The lack of heat is a very strong indicator that his primary issue is NOT, "leaves in the radiator".

 

I don't trust new thermostats without "testing" them in a pot of boiling water on the stove along with an accurate thermometer. I have been buying quality thermostats and have good luck but there are lots of new defective thermostats being made in China out there. It doesn't take long to verify it works before using it.

Also be sure that your Overflow Bottle is still working properly. I would install a new radiator cap and then check or replace the hose that goes down to the overflow bottle. The Bottle should have coolant up to the cold line when cool and as the engine warms up and the coolant expands and goes into the overflow bottle and the coolant level rises inside the overflow bottle Then as the engine cools it draws the coolant back into the radiator from the overflow Bottle. This is done thru vacuum so the hose and the connections at both ends should be secured and verified.

If this system is not functioning or the hose is leaking between the radiator cap and the overflow bottle your radiator will draw air to replace the coolant that was pushed out. This overflow system is crucial to the normal operation of the cooling system. Otherwise you end up with a good deal of air inside the radiator and that blocks the coolant from doing it's job.

After rebuilding or building a new engine, the engine could be expected to run a bit hotter than normal for the first few miles as it breaks in.
Your fans sound like they are doing exactly what they are supposed to do with the factory temperature settings.

Last but not least is how much anti-freeze is in your coolant mixture? I have seen engines overheat due to excessive anti-freeze in the coolant. I even saw one vehicle with 100% anti-freeze in it, needless to see it needed help. I run 70% Distilled water and 30% anti-freeze and I only use the old green anti-freeze in my 1988 Corvette.

 

Seems like coolant is not circulating well, WP does not need to weep to have failed. I'd suspect a gum up somewhere. Whole system flush and/or new WP likely needed.

On a 95, wouldn't be a bad idea to try the electric WPs if you wanted a little more performance out of it.

 

It needs more coolant!

 

Air pockets in the coolant is my first suspicion

 

You have several good comments from forum users to get your problem fixed... I want to comment on thermostat temp. I'm glad you kept a thermostat with the OEM temp of 180 F. Resist the temptation to install a lower temp thermostat to "make it run cooler." A lower temp thermostat will not make your engine run cooler at full warm up. It will cause your engine to stay in open loop longer and may cause it to not reach operating temp in shorter trips in cooler weather. I keep 195 F thermostats in my 85 and 88 as 195 is the OEM temp for those years.

 

Yeah? Won't run cooler but at the same time, won't make heat either? How does that work? Open loop threshold is WAY below even "cold" t-stat opening temps.


Give THIS a read.

 

I have read many threads (including the one you linked to) on CF regarding overheating and thermostat temps. I have seen threads where someone complains of running hot and people have suggested a lower temp thermostat, and this will NOT solve an overheating problem. If a thermostat opens at 180, 195, 210, etc., it will have no effect on the steady state temperature when the engine fully warms up. The ECM will control to whatever temp it is set to control, and the Thermostat (as long as it is not stuck open or closed) will not affect the running temp of a fully warmed L98/LT1 engine.. ... IF you have too low of a Thermostat (say 160 F), and you go on a short trip on a cold day, your engine may never reach fully operating temp because the Thermostat is opening too soon. In summer, this won't likely be a problem. ... You may be right about more HP at lower coolant temp, but the OP was not asking for more HP, he was trying to solve an overheating problem.

 

I have read many threads (including the one you linked to) on CF regarding overheating and thermostat temps. I have seen threads where someone complains of running hot and people have suggested a lower temp thermostat, and this will NOT solve an overheating problem. If a thermostat opens at 180, 195, 210, etc., it will have no effect on the steady state temperature when the engine fully warms up. The ECM will control to whatever temp it is set to control, and the Thermostat (as long as it is not stuck open or closed) will not affect the running temp of a fully warmed L98/LT1 engine.. ... IF you have too low of a Thermostat (say 160 F), and you go on a short trip on a cold day, your engine may never reach fully operating temp because the Thermostat is opening too soon. In summer, this won't likely be a problem. ... You may be right about more HP at lower coolant temp, but the OP was not asking for more HP, he was trying to solve an overheating problem.