Re: engine under heating /not heating up enough

[baily144]

Hi

2003 astro cargo van RWD

so I changed the engine in April ....and have had this issue ever since. the engine was from a 2005 blazer

the engine go's to cold after the stat opens .... I ran a live data test with a code scanner.

started engine .....drove at city speeds ...temp rose normally to 197 F ...you could see the stat open . then it plummets down to 180/183 area. Slowly comes up and levels off around 185 to 188 F. the gage reflects that temp.
There is little to no pressure build up at all
there no leaks i can see
the fluid level does not decrease either in the rad or bottle
there's lots of cab heat
its does not overheat and never has
engine runs fine with no codes or issues

this what I have done so far

4 different thermostats ...including AC Delco all 195 temp no change current is a Moterrad stat with a jiggle pin
tried everyway to burp out air ...i still get some small bubbles.
two new pressure caps ....current is AC Delco

im lost and no one can tell me why its doing this ......pressure test has been suggested but i have not done it yet.

Does anyone have any ..any suggestions ?

On a side note .... I ran the same test on my trailblazer ....it went to 197 F thermostat opened dropped to 191193 then went up to 195 and stayed there .....with loads of pressure on the hoses

any thoughts ....Alex

[Rod's Trucks]

Baily144,
Is it possible the temp sender in the replacement motor is reading the temp incorrectly and sending the wrong information to the scanner?
Just a thought, since that was probably the one that came with the replacement motor.
I see you were getting temps from the scanner, so they should be as accurate as the temp sender device is, but that sender could be 'off' by a little bit also. Being 'off' by just 5% could account for you difference in readings.
I hope you are not trying to read the temperature very accurately with the dash gauge. I would expect it to be mostly a 'relative' indicator to tell when something changes from whatever it indicates 'normally'..
For me, if it runs well and you get heat as you need and it runs at 185 or 187 consistently, I would not be concerned.
I have had many different vehicles that show similar sequences, where the temp rises to just above the 'standard' operational spot on the gauge, but just momentarily as the engine temp warms up.
The thermostat with the small open port or the 'wiggle pin' seems to help some, but the condition is still apparent if observed closely.
Rod J.
Issaquah, Wa

[baily144]

Hi.... Thanks for your help.... And that's what most people say... But... Why no pressure? You literally can drive hwy for 30 mins and pull the rad cap off. Sometimes.... There's a little pressure but not the rock hard hose before the engine change.

Regards Alex

[AlpineVan]

If you're losing pressure, and you're still getting small bubbles when you burp it, something tells me you're losing coolant somewhere.

[dchan51360]

Why are you thinking there should be a huge amount of pressure build up if your system is staying under 200 degrees.

Water does not expand that much (or coolant) the pump is not designed to increase pressure in your system, It's designed to move the water through the system.

The only reason you should be building up enough pressure to make all the hoses rock hard, are if you are creating enough steam ie boiling the coolant to create pressure. Running at a consistent 197 should not boil the coolant. and if you start to surpass that temp, then you might start to increase pressure and that's where the pressure cap starts to do its job.. It's job is to keep the coolant from "boiling" by "pressurizing" the system so that the temp can go above the standard 212 degrees (at sea level) without boiling.


Just trying to get a better understanding what's driving your question...

[baily144]

Hi... Thanks for the help

Isn't it supposed to pressurize the system... It did before, it also fully heated up before the engine change. Maybe I'm confused but every car I've Seen pressurized when running.

Doesn't the pressure in the system promote flow? Which there really isn't.

Again the trailblazer.. Pressurizes almost immediately after starting.

If I'm wrong ok.... But something that did something before but isn't now seems wrong.

Alex

[AstroWill]

Do a pressure test, easiest way to find a leak.

[baily144]

Hi... Thanks.... I'm in the process of getting that done... How much pressure and how long should it hold it? If I made an error I think it's a bolt that's into a water jacket... I didn't put thread sealer on it... That's the only thing I can think of.

BTW I figured out why the fuel trims were pegged out at idle... Maf sensor was only reporting 3.4 grams per second at idle. Lessons learned use a GM MAF sensor... Not a knock off piece of junk.

Alex

[dchan51360]

Pressurized yes but not to "rock hard" hoses. The one exception may be the output of the water pump. The hoses should get firm but in my experience they don't get "rock hard"
.
There should probably be about 7-10lbs of pressure with the engine running normally which will keep water from boiling out of the coolant.

[baily144]

Makes sence.... I used a poor choice of words.. Sry. The hoses are soft... Once in awhile slight pressure... But definitely not firm by any means.

Alex

[Mmusicman]

Cold weather temps can typically cause the system to run a little lower than thermost value.

You also need to be certain you are using the correct thermostat (with bypass valve)
When main valve opens, the bypass valve closes (and visa versa)
They control two different coolant routes.

Should look like this...

thermostat-bypass300.jpg (18.58 KiB) Viewed 146 times