Compression Test at Less Than Full Operating Temp

[idi_econoline]

Getting ready to do a procrastinated compression test, to hunt down a chuffing valve.

But, before parking my beast, my factory temp gauge indicated cooler running. Only up to the "N"..... haven't temp gunned this, but I'm assuming my thermostat (1 year old, from the Int'l stealer) isn't closing properly.

Should I change the stat before doing the compression test, to get a higher temp? Or could I just cheat by plugging in the block heater?

Guessing the answer here is not the shortcut....

 

[Kevin 007]

I have done many compression test on cold engines with VERY similar results to hot one. Some say that this is due to the oil jets lubing the underside of the piston skirts.

Im around 450psi cold, and very happy with it.

 

[riotwarrior]

do it cold...don't sweat it ...

JM2CW...

Al

 

[idi_econoline]

Thx, fellas. Sticking my long arms into that hot compartment is something I'm glad to avoid.

 

[Wyreth]

Also I would use a laser thermometer to check your water temp before assuming your thermostat is bad. Especially given how wonderfully accurate the ford gauges are.

 

[idi_econoline]

You betcha, Wyreth. Will be driving it on a gentle errand tomorrow. Temp gun is ready to go along.

Got a Motorcraft stat in my parts tub, just in case. MUCH easier with the engine out.

 

[idi_econoline]

I prefer REAL numbers, so I have an AutoMeter pillar pod waiting (for an Econoline, go figure!), with Isspro gauges from Conestoga Diesel.

But, first things first. (chuffchuffchuff)

 

[GOOSE]

You are looking for a difference between cylinders more so than the absolute best compression that a warm engine can muster. I wouldn't sweat it and do the test on a cold engine that is much more pleasant to work on. If the chuff is there when the engine is cold, the compression test will show you where most likely. I'm guessing the valve train is the culprit.

 

[idi_econoline]

Yes, GOOSE, it does, indeed, chuff when cold, though much less than the chuffing videos on other threads. So, yeah, I see that now: if it's chuffing cold, the compression will show lower on that cylinder. <lightbulb goes on>

I am hoping that it is the valve train, GOOSE. Will be changing lifters and pushrods all around anyway. Will also put on a new rocker-pair on whichever cylinder is the culprit.

I'm also suspecting that it's the valve train, as my heads were reconditioned by a reputable shop, and I have removed both valve covers enough to see NO blowby on either bank.

 

[GOOSE]

I would make sure to put an aftermarket oil pressure gauge. My relief valve in the oil cooler header got stuck causing an excess of oil pressure to hydrolock the lifters resulting in bent pushrods. The factory oil pressure gauge never indicated anything abnormal. I'm not saying that this is the crux of your issues, its just reassuring to know what the oil pressure is. The factory gauge simply tells you that there is at least 7psi.

Sent from my EVO using Tapatalk

 

[idi_econoline]

Aha, never thought of that, GOOSE. Although my problems started immediately at first startup with the reconditioned heads, this check is a wise idea. <lightbulb, again>

Actually, very easy for me to set up temporarily: the OP sender is easily accessed with the inside "doghouse" cover off. Won't get that together today, but will soon.

 

[idi_econoline]

Had the beast rolling, on a necessary errand today. For the record, the temp gauge made it to its usual reading (left part of "N"), and my temp gun gave me readings of low 150s at stat housing and temperature sender. Top tank of radiator was about 120!

Well, dang!