Will Not Reach Normal Operating Temperature

[jswiftsr]

1995 Chev Astro VIN:W CPI

I have a 1995 Chevrolet Astro Van. I had the engine rebuilt about 9 years ago. I don't remember if it did it from the start or not, but the engine temp will not get over 155 degrees. I put 3 different thermostats in it. The last one came from GM. They were all 195 degree thermostats.
I had a check engine light going for a little while, and corrected it with a new O2 Sensor. It has a slight skip, so I was thinking it has a head gasket blown from cylinder to cylinder, because I was not losing water or burning antifreeze, and pressure was not building in the radiator.

I did a compression test yesterday. When I pulled all the plugs, I do know it has been running rich due to the O2 sensor. Looking into the plug holes, it looks black "sutty" and the exhaust pipe is black as well. Now that I have taken the compression test (All cylinders 128 - 135) I am running out of ideas.

But I have tried about everything I know to get the engine temp up.....no heat in the winter months makes for cold driving. Could the injector be the culprit? Bad regulator? defective poppets? The fuel pressure leaks down back to the tank. But holds when I clamped off the supply line. Pressure is about 60 psi. (fuel pump / fuel filter, replaced a few years ago). in 10 years, I have only drove the van about 35K due to trying to get this problem resolved. It is also not the temperature sending unit. Coolant temperature matches gauge. and I have put a new coolant temperature sensor in it also.

Thanks in Advance.

 

[skylark]

There is only one possibility. The heater hoses are incorrectly routed. The coolant has to be bypassing the thermostat by pushing coolant through the heater core and into the radiator. You could test this by pinching off the heater hose and watch your temperature rise.

 

[evilunclegrimace]

try putting a sheet of cardboard in front of the radiator and see if the temp comes up while driving

 

[jswiftsr]

try putting a sheet of cardboard in front of the radiator and see if the temp comes up while driving

For the heater hose routing, one is coming off the water pump and the other off of the intake. Both go to the heat control valve. When heat is on, the water circulates through the heater core. When the heat is off, it bypasses the heater core and routes the water right back to the engine. So if the hoses were backward (thought about that already, and checked shop manual and made sure they were routed correctly) when the heat is off, the water is routed as if the heater core does not exist.

As for the cardboard, I have not tried that because I have a 2004 Astro that works fine, and I am trying to find a cause as to why this one is not. Now when I had the long block rebuilt, I used the same intake that was on the first engine. I ran the old engine extremely hot, trying to get it home when I bought the van. Could a cracked intake (if it was) cause this issue? I have tried everything else I know of, and am running out of ideas. Never in my life have I encountered such a problem.

 

[454cid]

Get an IR thermometer and start checking the temperature at the water neck, hoses, and so on. You should be getting heat at 155.... not great heat, but still heat. I'm thinking the engine is likely getting up to temperature, but your blend door is not funtioning correctly, or is mostly plugged or something.

 

[Crankshaft Brad]

I have had this exact problem with my 91’ 1/2ton 4.3 5-speed trans. I have found success with blocking off the radiator with cardboard in the winter. I smoked a rod bearing and yanked the engine. I pulled the engine apart paying attention to anything that would have affected the flow of coolant, and came up with nothing. I had my radiator checked out and it was not clogged, but replaced it for piece of mind. I pulled the heater core and dumped it out hoping to find gunk, but came up empty handed. My entire cooling system was flawless. I pulled my dash to check the blend door to make sure it worked, and was flawless (my blend door is manually/cable actuated). You aren’t the only one with this problem!

 

[CKVortec]

I did a compression test yesterday. When I pulled all the plugs, I do know it has been running rich due to the O2 sensor. Looking into the plug holes, it looks black "sutty" and the exhaust pipe is black as well. Now that I have taken the compression test (All cylinders 128 - 135)

It is also not the temperature sending unit. Coolant temperature matches gauge. and I have put a new coolant temperature sensor in it also.

Thanks in Advance.

First off, your compression test is pretty poor.
I'm wondering how you verified the coolant temperature and if you made sure you have the correct temperature sender.

I'm a little puzzled about you having a new t-stat and still not getting above 155, but one thing that I've seen for not building much heat is the fan clutch being seized and spinning at full engine RPM all the time instead of locking up only when hot.

Good luck!

 

[jswiftsr]

Get an IR thermometer and start checking the temperature at the water neck, hoses, and so on. You should be getting heat at 155.... not great heat, but still heat. I'm thinking the engine is likely getting up to temperature, but your blend door is not funtioning correctly, or is mostly plugged or something.

I put a temp Probe with my fluke digital meter in the radiator. I also tested it at the tstat neck and the heater hoses with an IR Thermometer. they all matched the temp gauge, 155 degrees. I have little heat blowing through the vents, with heat on. But a blend door is key to heat in the vehicle, but irrelevant to engine temp.

 

[Hipster]

I saw the compression test and wondered if the throttle plates were held open for it. 128-135 is pretty low. All plugs out, throttle open, take the compression reading on the third revolution on each cylinder. Just asking if that's about how it was done.

How long was it run pig rich? Possible you washed the rings?

 

[jswiftsr]

First off, your compression test is pretty poor.
I'm wondering how you verified the coolant temperature and if you made sure you have the correct temperature sender.

I'm a little puzzled about you having a new t-stat and still not getting above 155, but one thing that I've seen for not building much heat is the fan clutch being seized and spinning at full engine RPM all the time instead of locking up only when hot.

Good luck!

Verified temp explanation in above reply. Installed new temp sender and coolant temp sensor for computer. When I first installed the rebuilt engine I installed a new radiator (correct application) and a new fan clutch. For a few years after the fan sounded like it was revving most of the time when I drove it. Temp 155 degrees. Then I figured out Auto Zone sold me the wrong fan clutch. So I got the correct clutch, and that resolved my fan problem, but engine temp is still 155....summer and winter.