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Full Version: ECT Engine Coolant Temp / Radiator Config
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1995 GMC Jimmy 4.3 L vortek SLT 4wd

New Block installed. < 5000 miles new engine

Question about Coolant concentration / Radiator Configuration ?
Coolant Temp guage never reaching
Operating Temperature, unless sit
Idling with vehicle stationary. Once Air
received -- while driving , temp sitting at 120 - 155 degree F .
A/C condensor radiator is removed, as most all A/C components, as well. Vehicle is receiving direct front grill Air
to the Coolant Radiator.
Stock mechanical Cooling Fan removed - replaced w/ 14 amp electric fan with
manual interior dash board switch.
Antifreeze has some remaining Koolaid
additive from summer. Have deluted it some
removing Antifreeze and adding distilled water.
Need to do a complete radiator flush refill ?
Since I don't have front A/C condensor radiator , should I consider a plexiglass Air Block in which the Diesel Truck's use in winter to regulate Engine Coolant Temp. This dependent on seasonal weather conditions . . .
What would you suggest I try to get Engine Coolant Temp to a steady Operating Temp of 190 - 210 degree F ?
Still haven't got all the bugs worked out, eh? (LOL) I should talk, as I also have a project car in the wings.

Ok, let's address this one thing at a time and see where it goes....

Radiator configuration can be either conventional or cross flow, although my personal leaning is toward cross flow with a recovery tank because it's easier to keep the air out of the cooling system.

Coolant concentration should be a 50/50 mix pretty much no matter where you live. It will protect against freezing to -25 and also raise the boiling point to well beyond 250 degrees with a pressure cap. Antifreeze will also give you better heat transfer than straight water. If you buy "pre mixed" coolant it will be cut to 50/50 with GOOD water that will not leave mineral deposits. (distilled or deionized water) If you go this route then flush it clean first!

If the engine temp is that low then you have a t-stat problem. Get a 190 or 195 t-stat installed and buy a brand name so it wont fail in a year or two. I believe the proper t-stat for that will have an o-ring so nothing leaks by when the t-stat is closed.

If you have removed the AC condenser there's really no need to block the air flow unless the outside temps fall way below freezing on a regular basis. (we're talking single digits or lower) Regulating engine temp is a function of the t-stat unless it's so cold that there's too much heat being lost from the outside of the engine block, in which case you should get a cord of fire wood and a case of brandy to drink... then stay home!

NAPA (and others) offer aftermarket fan controls for that electric cooling. You can also use sensors with a relay similar to many stock GM options. 80's and 90's vintage Camaro is one off the top of my head. I used a mechanical (and adjustable) unit from NAPA for my last custom job that has a probe inside the top radiator hose. The fan only runs when the engine is over 200 degrees and will "after run" to prevent vapor lock. (wired hot all the time) At that amp draw for the fan you'd want to use a relay rated for at least 20 amps. A universal relay for lighting or "high blow" heater motor is commonly available. I can probably talk you through the wiring if necessary.

At any rate it sounds like you are making progress so keep us posted!
It sounds like the Thermostat isn’t working properly, either stuck open or bypassing too much. If it was working like it is supposed to the air flow through the radiator shouldn’t have to much effect on the engine temperature. If the thermostat is closed the airflow should only cool the water that is in the radiator. The thermostat should’t open until the engine temperature reaches around 195*. It has been a long time since I’ve worked on a 4.3; but if I remember correctly, that thermostat is sealed with an O-ring. Yet; for some strange reason, you can buy a gasket for the housing? Using a gasket allows the thermostat to come loose and bypass coolant. Allowing also for a plain defective thermostat, that gives you 3 things to consider in that area.

Another possibility is that you still have an Air Pocket in the system. At idle the coolant is touching the temperature senders and sending a higher reading to the gauge. At road speed the water pump is pulling coolant away from the sender making it show a cooler reading.

Hopefully that will give you some options to think about unless Rupe has some other insight that I have missed. Either way, please let us know what you find.
Garner makes a good point about that t-stat gasket versus the o-ring. 1995 was a change-over year and they had it both ways... with and without the gasket. The replacement is based on a W in the VIN for just an o-ring. (OEM engine) Without the W it was the early one with a gasket only. Typically there's a small machined lip on the top surface of the manifold for the o-ring where the t-stat goes. Let's put it this way, if it will seal with just an o-ring and you have that lip then that's what you should use. If you use both then coolant will get by the t-stat and it will run cold.
Thanks - Rupe and Garner.

I had thought ( I didn't install one ) I was running without a thermostat. I verified this.
Installed a new 195 degree Carquest
Thermostat, yesterday. Much better.
Thanks for the follow up. It may help someone else reading here.
I also thank you for the follow up. So few people take the time. Knowing what the "fix" was is very helpful.
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